include/linux/damon.h | 3 ++ mm/damon/dbgfs.c | 1 + mm/damon/vaddr.c | 147 ++++++++++++++++++++++++++++++++++++++++++++++++++ mm/internal.h | 2 + mm/vmscan.c | 4 +- 5 files changed, 155 insertions(+), 2 deletions(-)
Hi, Now on tiered memory system with different memory types, the reclaim path in shrink_page_list() already support demoting pages to slow memory node instead of discarding the pages. However, at that time the fast memory node memory wartermark is already tense, which will increase the memory allocation latency during page demotion. So a new method from user space demoting cold pages proactively will be more helpful. We can rely on the DAMON in user space to help to monitor the cold memory on fast memory node, and demote the cold pages to slow memory node proactively to keep the fast memory node in a healthy state. This patch set introduces a new scheme named DAMOS_DEMOTE to support this feature, and works well from my testing. Any comments are welcome. Thanks. Changes from v1: - Reuse the demote_page_list(). - Fix some comments style issues. - Move the DAMOS_DEMOTE definition to the correct place. - Rename some function name. - Change to return void type for damos_isolate_page(). - Remove unnecessary PAGE_ALIGN() in damos_demote(). - Fix the return value for damos_demote(). Baolin Wang (2): mm: Export the demote_page_list() function mm/damon: Add a new scheme to support demotion on tiered memory system include/linux/damon.h | 3 ++ mm/damon/dbgfs.c | 1 + mm/damon/vaddr.c | 147 ++++++++++++++++++++++++++++++++++++++++++++++++++ mm/internal.h | 2 + mm/vmscan.c | 4 +- 5 files changed, 155 insertions(+), 2 deletions(-) -- 1.8.3.1
On Wed, 22 Dec 2021 19:14:39 +0800 Baolin Wang <baolin.wang@linux.alibaba.com> wrote: > Now on tiered memory system with different memory types, the reclaim path in > shrink_page_list() already support demoting pages to slow memory node instead > of discarding the pages. However, at that time the fast memory node memory > wartermark is already tense, which will increase the memory allocation latency > during page demotion. So a new method from user space demoting cold pages > proactively will be more helpful. > > We can rely on the DAMON in user space to help to monitor the cold memory on > fast memory node, and demote the cold pages to slow memory node proactively to > keep the fast memory node in a healthy state. > > This patch set introduces a new scheme named DAMOS_DEMOTE to support this feature, > and works well from my testing. Any comments are welcome. Thanks. This is interesting. I think it would be helpful if we could have some example scenarios in this changelog, help people understand how to use DAMOS_DEMOTE and what effects it has. Documentation/admin-guide/mm/damon/usage.rst would like an update? And the DAMON user space tool?
On 12/23/2021 8:01 AM, Andrew Morton wrote: > On Wed, 22 Dec 2021 19:14:39 +0800 Baolin Wang <baolin.wang@linux.alibaba.com> wrote: > >> Now on tiered memory system with different memory types, the reclaim path in >> shrink_page_list() already support demoting pages to slow memory node instead >> of discarding the pages. However, at that time the fast memory node memory >> wartermark is already tense, which will increase the memory allocation latency >> during page demotion. So a new method from user space demoting cold pages >> proactively will be more helpful. >> >> We can rely on the DAMON in user space to help to monitor the cold memory on >> fast memory node, and demote the cold pages to slow memory node proactively to >> keep the fast memory node in a healthy state. >> >> This patch set introduces a new scheme named DAMOS_DEMOTE to support this feature, >> and works well from my testing. Any comments are welcome. Thanks. > > This is interesting. > > I think it would be helpful if we could have some example scenarios in > this changelog, help people understand how to use DAMOS_DEMOTE and what > effects it has. Sure. > > Documentation/admin-guide/mm/damon/usage.rst would like an update? Ah, I missed updating de Doc, and will do in v3. > And the DAMON user space tool? Yes. Thanks for your comments.
Baolin Wang <baolin.wang@linux.alibaba.com> writes: > Hi, > > Now on tiered memory system with different memory types, the reclaim path in > shrink_page_list() already support demoting pages to slow memory node instead > of discarding the pages. However, at that time the fast memory node memory > wartermark is already tense, which will increase the memory allocation latency > during page demotion. So a new method from user space demoting cold pages > proactively will be more helpful. > > We can rely on the DAMON in user space to help to monitor the cold memory on > fast memory node, and demote the cold pages to slow memory node proactively to > keep the fast memory node in a healthy state. > > This patch set introduces a new scheme named DAMOS_DEMOTE to support this feature, > and works well from my testing. Any comments are welcome. Thanks. As a performance optimization patch, it's better to provide some test results. Another question is why we shouldn't do this in user space? With DAMON, it's possible to export cold memory regions information to the user space, then we can use move_pages() to migrate them from DRAM to PMEM. What's the problem of that? Best Regards, Huang, Ying > Changes from v1: > - Reuse the demote_page_list(). > - Fix some comments style issues. > - Move the DAMOS_DEMOTE definition to the correct place. > - Rename some function name. > - Change to return void type for damos_isolate_page(). > - Remove unnecessary PAGE_ALIGN() in damos_demote(). > - Fix the return value for damos_demote(). > > Baolin Wang (2): > mm: Export the demote_page_list() function > mm/damon: Add a new scheme to support demotion on tiered memory system > > include/linux/damon.h | 3 ++ > mm/damon/dbgfs.c | 1 + > mm/damon/vaddr.c | 147 ++++++++++++++++++++++++++++++++++++++++++++++++++ > mm/internal.h | 2 + > mm/vmscan.c | 4 +- > 5 files changed, 155 insertions(+), 2 deletions(-)
On 12/23/2021 9:07 AM, Huang, Ying wrote: > Baolin Wang <baolin.wang@linux.alibaba.com> writes: > >> Hi, >> >> Now on tiered memory system with different memory types, the reclaim path in >> shrink_page_list() already support demoting pages to slow memory node instead >> of discarding the pages. However, at that time the fast memory node memory >> wartermark is already tense, which will increase the memory allocation latency >> during page demotion. So a new method from user space demoting cold pages >> proactively will be more helpful. >> >> We can rely on the DAMON in user space to help to monitor the cold memory on >> fast memory node, and demote the cold pages to slow memory node proactively to >> keep the fast memory node in a healthy state. >> >> This patch set introduces a new scheme named DAMOS_DEMOTE to support this feature, >> and works well from my testing. Any comments are welcome. Thanks. > > As a performance optimization patch, it's better to provide some test > results. Actually this is a functional patch, which adds a new scheme for DAMON. And I think it is too early to measure the performance for the real workload, and more work need to do for DAMON used on tiered memory system (like supporting promotion scheme later). > Another question is why we shouldn't do this in user space? With DAMON, > it's possible to export cold memory regions information to the user > space, then we can use move_pages() to migrate them from DRAM to PMEM. > What's the problem of that? IMO this is the purpose of introducing scheme for DAMON, and you can check more in the Documentation/admin-guide/mm/damon/usage.rst. " Schemes ------- For usual DAMON-based data access aware memory management optimizations, users would simply want the system to apply a memory management action to a memory region of a specific access pattern. DAMON receives such formalized operation schemes from the user and applies those to the target processes. "
Baolin Wang <baolin.wang@linux.alibaba.com> writes: > On 12/23/2021 9:07 AM, Huang, Ying wrote: >> Baolin Wang <baolin.wang@linux.alibaba.com> writes: >> >>> Hi, >>> >>> Now on tiered memory system with different memory types, the reclaim path in >>> shrink_page_list() already support demoting pages to slow memory node instead >>> of discarding the pages. However, at that time the fast memory node memory >>> wartermark is already tense, which will increase the memory allocation latency >>> during page demotion. So a new method from user space demoting cold pages >>> proactively will be more helpful. >>> >>> We can rely on the DAMON in user space to help to monitor the cold memory on >>> fast memory node, and demote the cold pages to slow memory node proactively to >>> keep the fast memory node in a healthy state. >>> >>> This patch set introduces a new scheme named DAMOS_DEMOTE to support this feature, >>> and works well from my testing. Any comments are welcome. Thanks. >> As a performance optimization patch, it's better to provide some >> test >> results. > > Actually this is a functional patch, which adds a new scheme for > DAMON. And I think it is too early to measure the performance for the > real workload, and more work need to do for DAMON used on tiered > memory system (like supporting promotion scheme later). I don't think you provide any new functionality except the performance influence. And I think proactive demotion itself can show some performance benefit already. Just like we can find the performance benefit in the proactive reclaim patchset as below. https://lore.kernel.org/lkml/20211019150731.16699-1-sj@kernel.org/ >> Another question is why we shouldn't do this in user space? With DAMON, >> it's possible to export cold memory regions information to the user >> space, then we can use move_pages() to migrate them from DRAM to PMEM. >> What's the problem of that? > > IMO this is the purpose of introducing scheme for DAMON, and you can > check more in the Documentation/admin-guide/mm/damon/usage.rst. > > " > Schemes > ------- > > For usual DAMON-based data access aware memory management > optimizations, users > would simply want the system to apply a memory management action to a memory > region of a specific access pattern. DAMON receives such formalized > operation > schemes from the user and applies those to the target processes. > " For proactive reclaim, we haven't a user space ABI to reclaim a page of a process from memory to disk. So it appears necessary to add a kernel module to do that. But for proactive demotion, we already have a user space ABI (move_pages()) to demote a page of a process from DRAM to PMEM. What prevents you to do all these in the user space? And, I found there are MADV_XXX schemes too. Where the user space ABIs are available already. TBH, I don't know why we need these given there are already user space ABIs. Maybe this is a question for SeongJae too. Best Regards, Huang, Ying
On 12/23/2021 11:22 AM, Huang, Ying wrote: > Baolin Wang <baolin.wang@linux.alibaba.com> writes: > >> On 12/23/2021 9:07 AM, Huang, Ying wrote: >>> Baolin Wang <baolin.wang@linux.alibaba.com> writes: >>> >>>> Hi, >>>> >>>> Now on tiered memory system with different memory types, the reclaim path in >>>> shrink_page_list() already support demoting pages to slow memory node instead >>>> of discarding the pages. However, at that time the fast memory node memory >>>> wartermark is already tense, which will increase the memory allocation latency >>>> during page demotion. So a new method from user space demoting cold pages >>>> proactively will be more helpful. >>>> >>>> We can rely on the DAMON in user space to help to monitor the cold memory on >>>> fast memory node, and demote the cold pages to slow memory node proactively to >>>> keep the fast memory node in a healthy state. >>>> >>>> This patch set introduces a new scheme named DAMOS_DEMOTE to support this feature, >>>> and works well from my testing. Any comments are welcome. Thanks. >>> As a performance optimization patch, it's better to provide some >>> test >>> results. >> >> Actually this is a functional patch, which adds a new scheme for >> DAMON. And I think it is too early to measure the performance for the >> real workload, and more work need to do for DAMON used on tiered >> memory system (like supporting promotion scheme later). > > I don't think you provide any new functionality except the performance > influence. Fair enough. I mean for DAMON. > And I think proactive demotion itself can show some performance benefit > already. Just like we can find the performance benefit in the proactive Yes, I think so too. But now I am afraid I can not get some obvious performance benefit with current linux-next branch on tiered memory system, since the promotion patches are not there (yes, I can backport them into my local branch to test), meanwhile I may need more tuning for the demote scheme (such as tuning min-size, max-size, min-acc, max-acc, min-age, max-age to get a better performance) for the real workload. Now I just did a small step to add demotiong support for DAMON, so I do not expect some obvious performance gain now (more work need to research). But same as the proactive reclaim, I think this is on the right way for DAMON. Anyway, maybe some other people also curious the benefit, and I will do some measurement with DAMON demote scheme on mysql to show the performance results. Or do you have any other measurement suggestion? > reclaim patchset as below. > > https://lore.kernel.org/lkml/20211019150731.16699-1-sj@kernel.org/ > >>> Another question is why we shouldn't do this in user space? With DAMON, >>> it's possible to export cold memory regions information to the user >>> space, then we can use move_pages() to migrate them from DRAM to PMEM. >>> What's the problem of that? >> >> IMO this is the purpose of introducing scheme for DAMON, and you can >> check more in the Documentation/admin-guide/mm/damon/usage.rst. >> >> " >> Schemes >> ------- >> >> For usual DAMON-based data access aware memory management >> optimizations, users >> would simply want the system to apply a memory management action to a memory >> region of a specific access pattern. DAMON receives such formalized >> operation >> schemes from the user and applies those to the target processes. >> " > > For proactive reclaim, we haven't a user space ABI to reclaim a page of > a process from memory to disk. So it appears necessary to add a kernel > module to do that. > > But for proactive demotion, we already have a user space ABI > (move_pages()) to demote a page of a process from DRAM to PMEM. What > prevents you to do all these in the user space? > > And, I found there are MADV_XXX schemes too. Where the user space ABIs > are available already. TBH, I don't know why we need these given there > are already user space ABIs. Maybe this is a question for SeongJae too. From my understanding, schemes will simplify the design for user space to avoid implementing their own strategy according to the monitoring results, and more details in patch[1]. SeongJae may have more input for the purpose. [1] https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/commit/?id=1f366e421c8f69583ed37b56d86e3747331869c3
Baolin Wang <baolin.wang@linux.alibaba.com> writes: > On 12/23/2021 11:22 AM, Huang, Ying wrote: >> Baolin Wang <baolin.wang@linux.alibaba.com> writes: >> >>> On 12/23/2021 9:07 AM, Huang, Ying wrote: >>>> Baolin Wang <baolin.wang@linux.alibaba.com> writes: >>>> >>>>> Hi, >>>>> >>>>> Now on tiered memory system with different memory types, the reclaim path in >>>>> shrink_page_list() already support demoting pages to slow memory node instead >>>>> of discarding the pages. However, at that time the fast memory node memory >>>>> wartermark is already tense, which will increase the memory allocation latency >>>>> during page demotion. So a new method from user space demoting cold pages >>>>> proactively will be more helpful. >>>>> >>>>> We can rely on the DAMON in user space to help to monitor the cold memory on >>>>> fast memory node, and demote the cold pages to slow memory node proactively to >>>>> keep the fast memory node in a healthy state. >>>>> >>>>> This patch set introduces a new scheme named DAMOS_DEMOTE to support this feature, >>>>> and works well from my testing. Any comments are welcome. Thanks. >>>> As a performance optimization patch, it's better to provide some >>>> test >>>> results. >>> >>> Actually this is a functional patch, which adds a new scheme for >>> DAMON. And I think it is too early to measure the performance for the >>> real workload, and more work need to do for DAMON used on tiered >>> memory system (like supporting promotion scheme later). >> I don't think you provide any new functionality except the >> performance >> influence. > > Fair enough. I mean for DAMON. > >> And I think proactive demotion itself can show some performance benefit >> already. Just like we can find the performance benefit in the proactive > > Yes, I think so too. But now I am afraid I can not get some obvious > performance benefit with current linux-next branch on tiered memory > system, since the promotion patches are not there (yes, I can backport > them into my local branch to test), meanwhile I may need more tuning > for the demote scheme (such as tuning min-size, max-size, min-acc, > max-acc, min-age, max-age to get a better performance) for the real > workload. Now I just did a small step to add demotiong support for > DAMON, so I do not expect some obvious performance gain now (more work > need to research). But same as the proactive reclaim, I think this is > on the right way for DAMON. > > Anyway, maybe some other people also curious the benefit, and I will > do some measurement with DAMON demote scheme on mysql to show the > performance results. Or do you have any other measurement suggestion? For example, you can run 2 instances of workload, say, instance A and instance B. The memory size of instance A + B is larger than the size of the DRAM. And `numactl -m <DRAM node>` is used to run the instance, so that demotion will be triggered when DRAM is used up. Instance A is run at first, after some time, say several to tens seconds, instance B is run. With the original kernel, demotion will be triggered when run instance B, long latency may be triggered. With your patch, the proactive demotion will be triggered earlier to avoid the long latency at the cost of performance of instance A (may be just a little). We can also compare between DAMON based and the in-kernel LRU based cold page identification algorithm. >> reclaim patchset as below. >> https://lore.kernel.org/lkml/20211019150731.16699-1-sj@kernel.org/ > >>>> Another question is why we shouldn't do this in user space? With DAMON, >>>> it's possible to export cold memory regions information to the user >>>> space, then we can use move_pages() to migrate them from DRAM to PMEM. >>>> What's the problem of that? >>> >>> IMO this is the purpose of introducing scheme for DAMON, and you can >>> check more in the Documentation/admin-guide/mm/damon/usage.rst. >>> >>> " >>> Schemes >>> ------- >>> >>> For usual DAMON-based data access aware memory management >>> optimizations, users >>> would simply want the system to apply a memory management action to a memory >>> region of a specific access pattern. DAMON receives such formalized >>> operation >>> schemes from the user and applies those to the target processes. >>> " >> For proactive reclaim, we haven't a user space ABI to reclaim a page >> of >> a process from memory to disk. So it appears necessary to add a kernel >> module to do that. >> But for proactive demotion, we already have a user space ABI >> (move_pages()) to demote a page of a process from DRAM to PMEM. What >> prevents you to do all these in the user space? >> And, I found there are MADV_XXX schemes too. Where the user space >> ABIs >> are available already. TBH, I don't know why we need these given there >> are already user space ABIs. Maybe this is a question for SeongJae too. > > From my understanding, schemes will simplify the design for user space > to avoid implementing their own strategy according to the monitoring > results, and more details in patch[1]. SeongJae may have more input > for the purpose. > > [1] > https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/commit/?id=1f366e421c8f69583ed37b56d86e3747331869c3 Thanks a lot for your information. The commit log is helpful. It's good to avoid to change the source code of an application to apply some memory management optimization (for example, use DAMON + madvise()). But it's much easier to run a user space daemon to optimize for the application. (for example, use DAMON + other information + process_madvise()). And this kind of per-application optimization is kind of application specific policy. This kind of policy may be too complex and flexible to be put in the kernel directly. For example, in addition to DAMON, some other application specific or system knowledge may be helpful too, so we have process_madvise() for that before DAMON. Some more complex algorithm may be needed for some applications. And this kind of application specific policy usually need complex configuration. It's hard to export all these policy parameters to the user space as the kernel ABI. Now, DAMON schemes parameters are exported in debugfs so they are not considered ABI. So they may be changed at any time. But applications need some stable and well-maintained ABI. All in all, IMHO, what we need is a user space per-application policy daemon with the information from DAMON and other sources. Best Regards, Huang, Ying
Hi,
On Thu, 23 Dec 2021 15:51:18 +0800 "Huang, Ying" <ying.huang@intel.com> wrote:
> Baolin Wang <baolin.wang@linux.alibaba.com> writes:
>
> > On 12/23/2021 11:22 AM, Huang, Ying wrote:
> >> Baolin Wang <baolin.wang@linux.alibaba.com> writes:
> >>
> >>> On 12/23/2021 9:07 AM, Huang, Ying wrote:
> >>>> Baolin Wang <baolin.wang@linux.alibaba.com> writes:
> >>>>
> >>>>> Hi,
> >>>>>
> >>>>> Now on tiered memory system with different memory types, the reclaim path in
> >>>>> shrink_page_list() already support demoting pages to slow memory node instead
> >>>>> of discarding the pages. However, at that time the fast memory node memory
> >>>>> wartermark is already tense, which will increase the memory allocation latency
> >>>>> during page demotion. So a new method from user space demoting cold pages
> >>>>> proactively will be more helpful.
> >>>>>
> >>>>> We can rely on the DAMON in user space to help to monitor the cold memory on
> >>>>> fast memory node, and demote the cold pages to slow memory node proactively to
> >>>>> keep the fast memory node in a healthy state.
> >>>>>
> >>>>> This patch set introduces a new scheme named DAMOS_DEMOTE to support this feature,
> >>>>> and works well from my testing. Any comments are welcome. Thanks.
> >>>> As a performance optimization patch, it's better to provide some
> >>>> test
> >>>> results.
> >>>
> >>> Actually this is a functional patch, which adds a new scheme for
> >>> DAMON. And I think it is too early to measure the performance for the
> >>> real workload, and more work need to do for DAMON used on tiered
> >>> memory system (like supporting promotion scheme later).
> >> I don't think you provide any new functionality except the
> >> performance
> >> influence.
> >
> > Fair enough. I mean for DAMON.
> >
> >> And I think proactive demotion itself can show some performance benefit
> >> already. Just like we can find the performance benefit in the proactive
> >
> > Yes, I think so too. But now I am afraid I can not get some obvious
> > performance benefit with current linux-next branch on tiered memory
> > system, since the promotion patches are not there (yes, I can backport
> > them into my local branch to test), meanwhile I may need more tuning
> > for the demote scheme (such as tuning min-size, max-size, min-acc,
> > max-acc, min-age, max-age to get a better performance) for the real
> > workload. Now I just did a small step to add demotiong support for
> > DAMON, so I do not expect some obvious performance gain now (more work
> > need to research). But same as the proactive reclaim, I think this is
> > on the right way for DAMON.
> >
> > Anyway, maybe some other people also curious the benefit, and I will
> > do some measurement with DAMON demote scheme on mysql to show the
> > performance results. Or do you have any other measurement suggestion?
>
> For example, you can run 2 instances of workload, say, instance A and
> instance B. The memory size of instance A + B is larger than the size
> of the DRAM. And `numactl -m <DRAM node>` is used to run the instance,
> so that demotion will be triggered when DRAM is used up. Instance A is
> run at first, after some time, say several to tens seconds, instance B
> is run. With the original kernel, demotion will be triggered when run
> instance B, long latency may be triggered. With your patch, the
> proactive demotion will be triggered earlier to avoid the long latency
> at the cost of performance of instance A (may be just a little). We can
> also compare between DAMON based and the in-kernel LRU based cold page
> identification algorithm.
Good suggestion!
Also, there is a performance test for virtual address space proactive
reclamation scheme in the DAMON performance tests suite[1]. It measures memory
saving and runtime slowdown. Maybe you could start from extending that for
demote scheme and measure similar metrics.
[1] https://github.com/awslabs/damon-tests/tree/master/perf
>
> >> reclaim patchset as below.
> >> https://lore.kernel.org/lkml/20211019150731.16699-1-sj@kernel.org/
> >
> >>>> Another question is why we shouldn't do this in user space? With DAMON,
> >>>> it's possible to export cold memory regions information to the user
> >>>> space, then we can use move_pages() to migrate them from DRAM to PMEM.
> >>>> What's the problem of that?
> >>>
> >>> IMO this is the purpose of introducing scheme for DAMON, and you can
> >>> check more in the Documentation/admin-guide/mm/damon/usage.rst.
> >>>
> >>> "
> >>> Schemes
> >>> -------
> >>>
> >>> For usual DAMON-based data access aware memory management
> >>> optimizations, users
> >>> would simply want the system to apply a memory management action to a memory
> >>> region of a specific access pattern. DAMON receives such formalized
> >>> operation
> >>> schemes from the user and applies those to the target processes.
> >>> "
> >> For proactive reclaim, we haven't a user space ABI to reclaim a page
> >> of
> >> a process from memory to disk. So it appears necessary to add a kernel
> >> module to do that.
> >> But for proactive demotion, we already have a user space ABI
> >> (move_pages()) to demote a page of a process from DRAM to PMEM. What
> >> prevents you to do all these in the user space?
> >> And, I found there are MADV_XXX schemes too. Where the user space
> >> ABIs
> >> are available already. TBH, I don't know why we need these given there
> >> are already user space ABIs. Maybe this is a question for SeongJae too.
> >
> > From my understanding, schemes will simplify the design for user space
> > to avoid implementing their own strategy according to the monitoring
> > results, and more details in patch[1]. SeongJae may have more input
> > for the purpose.
> >
> > [1]
> > https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/commit/?id=1f366e421c8f69583ed37b56d86e3747331869c3
>
> Thanks a lot for your information. The commit log is helpful.
>
> It's good to avoid to change the source code of an application to apply
> some memory management optimization (for example, use DAMON +
> madvise()). But it's much easier to run a user space daemon to optimize
> for the application. (for example, use DAMON + other information +
> process_madvise()).
>
> And this kind of per-application optimization is kind of application
> specific policy. This kind of policy may be too complex and flexible to
> be put in the kernel directly. For example, in addition to DAMON, some
> other application specific or system knowledge may be helpful too, so we
> have process_madvise() for that before DAMON. Some more complex
> algorithm may be needed for some applications.
>
> And this kind of application specific policy usually need complex
> configuration. It's hard to export all these policy parameters to the
> user space as the kernel ABI. Now, DAMON schemes parameters are
> exported in debugfs so they are not considered ABI. So they may be
> changed at any time. But applications need some stable and
> well-maintained ABI.
>
> All in all, IMHO, what we need is a user space per-application policy
> daemon with the information from DAMON and other sources.
I basically agree to Ying, as I also noted in the coverletter of DAMOS
patchset[1]:
DAMON[1] can be used as a primitive for data access aware memory
management optimizations. For that, users who want such optimizations
should run DAMON, read the monitoring results, analyze it, plan a new
memory management scheme, and apply the new scheme by themselves. Such
efforts will be inevitable for some complicated optimizations.
[1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=fda504fade7f124858d7022341dc46ff35b45274
That is, I believe some programs and big companies would definitely have their
own information and want such kind of complicated optimizations. But, such
optimizations would depend on characteristics of each program and require
investment of some amount of resources. Some other programs and users wouldn't
have such special information, and/or resource to invest for such
optimizations. For them, some amount of benefit would be helpful enough even
though its sub-optimal.
I think we should help both groups, and DAMOS could be useful for the second
group. And I don't think DAMOS is useless for the first group. They could use
their information-based policy in prallel to DAMOS in some cases. E.g., if
they have a way to predict the data access pattern of specific memory region
even without help from DAMON, they can use their own policy for the region but
DAMOS for other regions.
Someone could ask why not implement a user-space implementation for the second
group, then. First of all, DAMOS is not only for the user-space driven virtual
memory management optimization, but also for kernel-space programs and any
DAMOS-supportable address spaces including the physical address space. And,
another important goal of DAMOS for user space driven use case in addition to
reducing the redundant code is minimizing the user-kernel context switch
overhead for passing the monitoring results information and memory management
action requests.
In summary, I agree the user space per-application policy daemon will be useful
for the specialized ultimate optimizations, but we also need DAMOS for another
common group of cases.
If I'm missing something, please feel free to let me know.
Thanks,
SJ
>
> Best Regards,
> Huang, Ying
Hi, SeongJae, SeongJae Park <sj@kernel.org> writes: > Hi, > > On Thu, 23 Dec 2021 15:51:18 +0800 "Huang, Ying" <ying.huang@intel.com> wrote: [snip] >> It's good to avoid to change the source code of an application to apply >> some memory management optimization (for example, use DAMON + >> madvise()). But it's much easier to run a user space daemon to optimize >> for the application. (for example, use DAMON + other information + >> process_madvise()). >> >> And this kind of per-application optimization is kind of application >> specific policy. This kind of policy may be too complex and flexible to >> be put in the kernel directly. For example, in addition to DAMON, some >> other application specific or system knowledge may be helpful too, so we >> have process_madvise() for that before DAMON. Some more complex >> algorithm may be needed for some applications. >> >> And this kind of application specific policy usually need complex >> configuration. It's hard to export all these policy parameters to the >> user space as the kernel ABI. Now, DAMON schemes parameters are >> exported in debugfs so they are not considered ABI. So they may be >> changed at any time. But applications need some stable and >> well-maintained ABI. >> >> All in all, IMHO, what we need is a user space per-application policy >> daemon with the information from DAMON and other sources. > > I basically agree to Ying, as I also noted in the coverletter of DAMOS > patchset[1]: > > DAMON[1] can be used as a primitive for data access aware memory > management optimizations. For that, users who want such optimizations > should run DAMON, read the monitoring results, analyze it, plan a new > memory management scheme, and apply the new scheme by themselves. Such > efforts will be inevitable for some complicated optimizations. > > [1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=fda504fade7f124858d7022341dc46ff35b45274 > > That is, I believe some programs and big companies would definitely have their > own information and want such kind of complicated optimizations. But, such > optimizations would depend on characteristics of each program and require > investment of some amount of resources. Some other programs and users wouldn't > have such special information, and/or resource to invest for such > optimizations. For them, some amount of benefit would be helpful enough even > though its sub-optimal. > > I think we should help both groups, and DAMOS could be useful for the second > group. And I don't think DAMOS is useless for the first group. They could use > their information-based policy in prallel to DAMOS in some cases. E.g., if > they have a way to predict the data access pattern of specific memory region > even without help from DAMON, they can use their own policy for the region but > DAMOS for other regions. > > Someone could ask why not implement a user-space implementation for the second > group, then. First of all, DAMOS is not only for the user-space driven virtual > memory management optimization, but also for kernel-space programs and any > DAMOS-supportable address spaces including the physical address space. And, > another important goal of DAMOS for user space driven use case in addition to > reducing the redundant code is minimizing the user-kernel context switch > overhead for passing the monitoring results information and memory management > action requests. > > In summary, I agree the user space per-application policy daemon will be useful > for the specialized ultimate optimizations, but we also need DAMOS for another > common group of cases. > > If I'm missing something, please feel free to let me know. I guess that most end-users and quite some system administrators of small companies have no enough capability to take advantage of the per-application optimizations. How do they know the appropriate region number and proactive reclaim threshold? So per my understanding, Linux kernel need provide, 1. An in-kernel general policy that is obviously correct and benefits almost all users and applications, at least no regression. No complex configuration or deep knowledge is needed to take advantage of it. 2. Some way to inspect and control system and application behavior, so that some advanced and customized user space policy daemons can be built to satisfy some advanced users who have the enough knowledge for the applications and systems, for example, oomd. Best Regards, Huang, Ying
Hello, On Mon, 27 Dec 2021 11:09:56 +0800 "Huang, Ying" <ying.huang@intel.com> wrote: > Hi, SeongJae, > > SeongJae Park <sj@kernel.org> writes: > > > Hi, > > > > On Thu, 23 Dec 2021 15:51:18 +0800 "Huang, Ying" <ying.huang@intel.com> wrote: > > [snip] > > >> It's good to avoid to change the source code of an application to apply > >> some memory management optimization (for example, use DAMON + > >> madvise()). But it's much easier to run a user space daemon to optimize > >> for the application. (for example, use DAMON + other information + > >> process_madvise()). > >> > >> And this kind of per-application optimization is kind of application > >> specific policy. This kind of policy may be too complex and flexible to > >> be put in the kernel directly. For example, in addition to DAMON, some > >> other application specific or system knowledge may be helpful too, so we > >> have process_madvise() for that before DAMON. Some more complex > >> algorithm may be needed for some applications. > >> > >> And this kind of application specific policy usually need complex > >> configuration. It's hard to export all these policy parameters to the > >> user space as the kernel ABI. Now, DAMON schemes parameters are > >> exported in debugfs so they are not considered ABI. So they may be > >> changed at any time. But applications need some stable and > >> well-maintained ABI. > >> > >> All in all, IMHO, what we need is a user space per-application policy > >> daemon with the information from DAMON and other sources. > > > > I basically agree to Ying, as I also noted in the coverletter of DAMOS > > patchset[1]: > > > > DAMON[1] can be used as a primitive for data access aware memory > > management optimizations. For that, users who want such optimizations > > should run DAMON, read the monitoring results, analyze it, plan a new > > memory management scheme, and apply the new scheme by themselves. Such > > efforts will be inevitable for some complicated optimizations. > > > > [1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=fda504fade7f124858d7022341dc46ff35b45274 > > > > That is, I believe some programs and big companies would definitely have their > > own information and want such kind of complicated optimizations. But, such > > optimizations would depend on characteristics of each program and require > > investment of some amount of resources. Some other programs and users wouldn't > > have such special information, and/or resource to invest for such > > optimizations. For them, some amount of benefit would be helpful enough even > > though its sub-optimal. > > > > I think we should help both groups, and DAMOS could be useful for the second > > group. And I don't think DAMOS is useless for the first group. They could use > > their information-based policy in prallel to DAMOS in some cases. E.g., if > > they have a way to predict the data access pattern of specific memory region > > even without help from DAMON, they can use their own policy for the region but > > DAMOS for other regions. > > > > Someone could ask why not implement a user-space implementation for the second > > group, then. First of all, DAMOS is not only for the user-space driven virtual > > memory management optimization, but also for kernel-space programs and any > > DAMOS-supportable address spaces including the physical address space. And, > > another important goal of DAMOS for user space driven use case in addition to > > reducing the redundant code is minimizing the user-kernel context switch > > overhead for passing the monitoring results information and memory management > > action requests. > > > > In summary, I agree the user space per-application policy daemon will be useful > > for the specialized ultimate optimizations, but we also need DAMOS for another > > common group of cases. > > > > If I'm missing something, please feel free to let me know. > > I guess that most end-users and quite some system administrators of > small companies have no enough capability to take advantage of the > per-application optimizations. How do they know the appropriate region > number and proactive reclaim threshold? > > So per my understanding, Linux kernel > need provide, > > 1. An in-kernel general policy that is obviously correct and benefits > almost all users and applications, at least no regression. No > complex configuration or deep knowledge is needed to take advantage > of it. > > 2. Some way to inspect and control system and application behavior, so > that some advanced and customized user space policy daemons can be > built to satisfy some advanced users who have the enough knowledge > for the applications and systems, for example, oomd. Agreed, and I think that's the approach that DAMON is currently taking. In specific, we provide DAMON debugfs interface for users who want to inspect and control their system and application behavior. Using it, we also made a PoC level user space policy daemon[1]. For the in-kernel policies, we are developing DAMON-based kernel components one by one, for specific usages. DAMON-based proactive reclamation module (DAMON_RECLAIM) is one such example. Such DAMON-based components will remove complex tunables that necessary for the general inspection and control of the system but unnecessary for their specific purpose (e.g., proactive reclamation) to allow users use it in a simple manner. Also, those will use conservative default configs to not incur visible regression. For example, DAMON_RECLAIM uses only up to 1% of single CPU time for the reclamation by default. In short, I think we're on the same page, and adding DEMOTION scheme action could be helpful for the users who want to efficiently inspect and control the system/application behavior for their tiered memory systems. It's unclear how much benefit this could give to users, though. I assume Baolin would come back with some sort of numbers in the next spin. Nevertheless, I personally don't think that's a critical blocker, as this patch is essentially just adding a way for using the pre-existing primitive, namely move_pages(), in a little bit more efficient manner, for the access pattern-based use cases. If I'm missing something, please feel free to let me know. [1] https://github.com/awslabs/damoos Thanks, SJ > > Best Regards, > Huang, Ying
SeongJae Park <sj@kernel.org> writes: > Hello, > > On Mon, 27 Dec 2021 11:09:56 +0800 "Huang, Ying" <ying.huang@intel.com> wrote: > >> Hi, SeongJae, >> >> SeongJae Park <sj@kernel.org> writes: >> >> > Hi, >> > >> > On Thu, 23 Dec 2021 15:51:18 +0800 "Huang, Ying" <ying.huang@intel.com> wrote: >> >> [snip] >> >> >> It's good to avoid to change the source code of an application to apply >> >> some memory management optimization (for example, use DAMON + >> >> madvise()). But it's much easier to run a user space daemon to optimize >> >> for the application. (for example, use DAMON + other information + >> >> process_madvise()). >> >> >> >> And this kind of per-application optimization is kind of application >> >> specific policy. This kind of policy may be too complex and flexible to >> >> be put in the kernel directly. For example, in addition to DAMON, some >> >> other application specific or system knowledge may be helpful too, so we >> >> have process_madvise() for that before DAMON. Some more complex >> >> algorithm may be needed for some applications. >> >> >> >> And this kind of application specific policy usually need complex >> >> configuration. It's hard to export all these policy parameters to the >> >> user space as the kernel ABI. Now, DAMON schemes parameters are >> >> exported in debugfs so they are not considered ABI. So they may be >> >> changed at any time. But applications need some stable and >> >> well-maintained ABI. >> >> >> >> All in all, IMHO, what we need is a user space per-application policy >> >> daemon with the information from DAMON and other sources. >> > >> > I basically agree to Ying, as I also noted in the coverletter of DAMOS >> > patchset[1]: >> > >> > DAMON[1] can be used as a primitive for data access aware memory >> > management optimizations. For that, users who want such optimizations >> > should run DAMON, read the monitoring results, analyze it, plan a new >> > memory management scheme, and apply the new scheme by themselves. Such >> > efforts will be inevitable for some complicated optimizations. >> > >> > [1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=fda504fade7f124858d7022341dc46ff35b45274 >> > >> > That is, I believe some programs and big companies would definitely have their >> > own information and want such kind of complicated optimizations. But, such >> > optimizations would depend on characteristics of each program and require >> > investment of some amount of resources. Some other programs and users wouldn't >> > have such special information, and/or resource to invest for such >> > optimizations. For them, some amount of benefit would be helpful enough even >> > though its sub-optimal. >> > >> > I think we should help both groups, and DAMOS could be useful for the second >> > group. And I don't think DAMOS is useless for the first group. They could use >> > their information-based policy in prallel to DAMOS in some cases. E.g., if >> > they have a way to predict the data access pattern of specific memory region >> > even without help from DAMON, they can use their own policy for the region but >> > DAMOS for other regions. >> > >> > Someone could ask why not implement a user-space implementation for the second >> > group, then. First of all, DAMOS is not only for the user-space driven virtual >> > memory management optimization, but also for kernel-space programs and any >> > DAMOS-supportable address spaces including the physical address space. And, >> > another important goal of DAMOS for user space driven use case in addition to >> > reducing the redundant code is minimizing the user-kernel context switch >> > overhead for passing the monitoring results information and memory management >> > action requests. >> > >> > In summary, I agree the user space per-application policy daemon will be useful >> > for the specialized ultimate optimizations, but we also need DAMOS for another >> > common group of cases. >> > >> > If I'm missing something, please feel free to let me know. >> >> I guess that most end-users and quite some system administrators of >> small companies have no enough capability to take advantage of the >> per-application optimizations. How do they know the appropriate region >> number and proactive reclaim threshold? >> >> So per my understanding, Linux kernel >> need provide, >> >> 1. An in-kernel general policy that is obviously correct and benefits >> almost all users and applications, at least no regression. No >> complex configuration or deep knowledge is needed to take advantage >> of it. >> >> 2. Some way to inspect and control system and application behavior, so >> that some advanced and customized user space policy daemons can be >> built to satisfy some advanced users who have the enough knowledge >> for the applications and systems, for example, oomd. > > Agreed, and I think that's the approach that DAMON is currently taking. In > specific, we provide DAMON debugfs interface for users who want to inspect and > control their system and application behavior. Using it, we also made a PoC > level user space policy daemon[1]. > > For the in-kernel policies, we are developing DAMON-based kernel components one > by one, for specific usages. DAMON-based proactive reclamation module > (DAMON_RECLAIM) is one such example. Such DAMON-based components will remove > complex tunables that necessary for the general inspection and control of the > system but unnecessary for their specific purpose (e.g., proactive reclamation) > to allow users use it in a simple manner. Also, those will use conservative > default configs to not incur visible regression. For example, DAMON_RECLAIM > uses only up to 1% of single CPU time for the reclamation by default. I don't think DAMON schemes are the in-kernel general policy I mentioned above (1.). For example, NUMA balancing is a general policy to optimize performance. It tries to provide a general policy that works for all users with as few as possible tunables. If some tunables are needed, they will be provided as ABI. Best Regards, Huang, Ying > In short, I think we're on the same page, and adding DEMOTION scheme action > could be helpful for the users who want to efficiently inspect and control the > system/application behavior for their tiered memory systems. It's unclear how > much benefit this could give to users, though. I assume Baolin would come back > with some sort of numbers in the next spin. Nevertheless, I personally don't > think that's a critical blocker, as this patch is essentially just adding a way > for using the pre-existing primitive, namely move_pages(), in a little bit more > efficient manner, for the access pattern-based use cases. > > If I'm missing something, please feel free to let me know. > > [1] https://github.com/awslabs/damoos > > > Thanks, > SJ > >> >> Best Regards, >> Huang, Ying
On Wed, 29 Dec 2021 09:33:56 +0800 "Huang, Ying" <ying.huang@intel.com> wrote: > SeongJae Park <sj@kernel.org> writes: > > > Hello, > > > > On Mon, 27 Dec 2021 11:09:56 +0800 "Huang, Ying" <ying.huang@intel.com> wrote: > > > >> Hi, SeongJae, > >> > >> SeongJae Park <sj@kernel.org> writes: > >> > >> > Hi, > >> > > >> > On Thu, 23 Dec 2021 15:51:18 +0800 "Huang, Ying" <ying.huang@intel.com> wrote: > >> > >> [snip] > >> > >> >> It's good to avoid to change the source code of an application to apply > >> >> some memory management optimization (for example, use DAMON + > >> >> madvise()). But it's much easier to run a user space daemon to optimize > >> >> for the application. (for example, use DAMON + other information + > >> >> process_madvise()). > >> >> > >> >> And this kind of per-application optimization is kind of application > >> >> specific policy. This kind of policy may be too complex and flexible to > >> >> be put in the kernel directly. For example, in addition to DAMON, some > >> >> other application specific or system knowledge may be helpful too, so we > >> >> have process_madvise() for that before DAMON. Some more complex > >> >> algorithm may be needed for some applications. > >> >> > >> >> And this kind of application specific policy usually need complex > >> >> configuration. It's hard to export all these policy parameters to the > >> >> user space as the kernel ABI. Now, DAMON schemes parameters are > >> >> exported in debugfs so they are not considered ABI. So they may be > >> >> changed at any time. But applications need some stable and > >> >> well-maintained ABI. > >> >> > >> >> All in all, IMHO, what we need is a user space per-application policy > >> >> daemon with the information from DAMON and other sources. > >> > > >> > I basically agree to Ying, as I also noted in the coverletter of DAMOS > >> > patchset[1]: > >> > > >> > DAMON[1] can be used as a primitive for data access aware memory > >> > management optimizations. For that, users who want such optimizations > >> > should run DAMON, read the monitoring results, analyze it, plan a new > >> > memory management scheme, and apply the new scheme by themselves. Such > >> > efforts will be inevitable for some complicated optimizations. > >> > > >> > [1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=fda504fade7f124858d7022341dc46ff35b45274 > >> > > >> > That is, I believe some programs and big companies would definitely have their > >> > own information and want such kind of complicated optimizations. But, such > >> > optimizations would depend on characteristics of each program and require > >> > investment of some amount of resources. Some other programs and users wouldn't > >> > have such special information, and/or resource to invest for such > >> > optimizations. For them, some amount of benefit would be helpful enough even > >> > though its sub-optimal. > >> > > >> > I think we should help both groups, and DAMOS could be useful for the second > >> > group. And I don't think DAMOS is useless for the first group. They could use > >> > their information-based policy in prallel to DAMOS in some cases. E.g., if > >> > they have a way to predict the data access pattern of specific memory region > >> > even without help from DAMON, they can use their own policy for the region but > >> > DAMOS for other regions. > >> > > >> > Someone could ask why not implement a user-space implementation for the second > >> > group, then. First of all, DAMOS is not only for the user-space driven virtual > >> > memory management optimization, but also for kernel-space programs and any > >> > DAMOS-supportable address spaces including the physical address space. And, > >> > another important goal of DAMOS for user space driven use case in addition to > >> > reducing the redundant code is minimizing the user-kernel context switch > >> > overhead for passing the monitoring results information and memory management > >> > action requests. > >> > > >> > In summary, I agree the user space per-application policy daemon will be useful > >> > for the specialized ultimate optimizations, but we also need DAMOS for another > >> > common group of cases. > >> > > >> > If I'm missing something, please feel free to let me know. > >> > >> I guess that most end-users and quite some system administrators of > >> small companies have no enough capability to take advantage of the > >> per-application optimizations. How do they know the appropriate region > >> number and proactive reclaim threshold? > >> > >> So per my understanding, Linux kernel > >> need provide, > >> > >> 1. An in-kernel general policy that is obviously correct and benefits > >> almost all users and applications, at least no regression. No > >> complex configuration or deep knowledge is needed to take advantage > >> of it. > >> > >> 2. Some way to inspect and control system and application behavior, so > >> that some advanced and customized user space policy daemons can be > >> built to satisfy some advanced users who have the enough knowledge > >> for the applications and systems, for example, oomd. > > > > Agreed, and I think that's the approach that DAMON is currently taking. In > > specific, we provide DAMON debugfs interface for users who want to inspect and > > control their system and application behavior. Using it, we also made a PoC > > level user space policy daemon[1]. > > > > For the in-kernel policies, we are developing DAMON-based kernel components one > > by one, for specific usages. DAMON-based proactive reclamation module > > (DAMON_RECLAIM) is one such example. Such DAMON-based components will remove > > complex tunables that necessary for the general inspection and control of the > > system but unnecessary for their specific purpose (e.g., proactive reclamation) > > to allow users use it in a simple manner. Also, those will use conservative > > default configs to not incur visible regression. For example, DAMON_RECLAIM > > uses only up to 1% of single CPU time for the reclamation by default. > > I don't think DAMON schemes are the in-kernel general policy I mentioned > above (1.). For example, NUMA balancing is a general policy to optimize > performance. It tries to provide a general policy that works for all > users with as few as possible tunables. If some tunables are needed, > they will be provided as ABI. Exactly. What I'm saying is, DAMON schemes that exposed to user space via the debugfs interface is for inspection of system and development of user space daemon (2.). It requires some level of tuning and doesn't provide stable ABI but the debugfs interface. Meanwhile, DAMON-based kernel components like DAMON_RECLAIM can be used for the in-kernel general policy (1.). For example, DAMON_RECLAIM also tries to be beneficial or at least incur no regression for almost every users, provides as few as possible tunables, and provides those via its ABI (module parameters), not debugfs. Thanks, SJ > > Best Regards, > Huang, Ying > > > In short, I think we're on the same page, and adding DEMOTION scheme action > > could be helpful for the users who want to efficiently inspect and control the > > system/application behavior for their tiered memory systems. It's unclear how > > much benefit this could give to users, though. I assume Baolin would come back > > with some sort of numbers in the next spin. Nevertheless, I personally don't > > think that's a critical blocker, as this patch is essentially just adding a way > > for using the pre-existing primitive, namely move_pages(), in a little bit more > > efficient manner, for the access pattern-based use cases. > > > > If I'm missing something, please feel free to let me know. > > > > [1] https://github.com/awslabs/damoos > > > > > > Thanks, > > SJ > > > >> > >> Best Regards, > >> Huang, Ying >
SeongJae Park <sj@kernel.org> writes: > On Wed, 29 Dec 2021 09:33:56 +0800 "Huang, Ying" <ying.huang@intel.com> wrote: > >> SeongJae Park <sj@kernel.org> writes: >> >> > Hello, >> > >> > On Mon, 27 Dec 2021 11:09:56 +0800 "Huang, Ying" <ying.huang@intel.com> wrote: >> > >> >> Hi, SeongJae, >> >> >> >> SeongJae Park <sj@kernel.org> writes: >> >> >> >> > Hi, >> >> > >> >> > On Thu, 23 Dec 2021 15:51:18 +0800 "Huang, Ying" <ying.huang@intel.com> wrote: >> >> >> >> [snip] >> >> >> >> >> It's good to avoid to change the source code of an application to apply >> >> >> some memory management optimization (for example, use DAMON + >> >> >> madvise()). But it's much easier to run a user space daemon to optimize >> >> >> for the application. (for example, use DAMON + other information + >> >> >> process_madvise()). >> >> >> >> >> >> And this kind of per-application optimization is kind of application >> >> >> specific policy. This kind of policy may be too complex and flexible to >> >> >> be put in the kernel directly. For example, in addition to DAMON, some >> >> >> other application specific or system knowledge may be helpful too, so we >> >> >> have process_madvise() for that before DAMON. Some more complex >> >> >> algorithm may be needed for some applications. >> >> >> >> >> >> And this kind of application specific policy usually need complex >> >> >> configuration. It's hard to export all these policy parameters to the >> >> >> user space as the kernel ABI. Now, DAMON schemes parameters are >> >> >> exported in debugfs so they are not considered ABI. So they may be >> >> >> changed at any time. But applications need some stable and >> >> >> well-maintained ABI. >> >> >> >> >> >> All in all, IMHO, what we need is a user space per-application policy >> >> >> daemon with the information from DAMON and other sources. >> >> > >> >> > I basically agree to Ying, as I also noted in the coverletter of DAMOS >> >> > patchset[1]: >> >> > >> >> > DAMON[1] can be used as a primitive for data access aware memory >> >> > management optimizations. For that, users who want such optimizations >> >> > should run DAMON, read the monitoring results, analyze it, plan a new >> >> > memory management scheme, and apply the new scheme by themselves. Such >> >> > efforts will be inevitable for some complicated optimizations. >> >> > >> >> > [1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=fda504fade7f124858d7022341dc46ff35b45274 >> >> > >> >> > That is, I believe some programs and big companies would definitely have their >> >> > own information and want such kind of complicated optimizations. But, such >> >> > optimizations would depend on characteristics of each program and require >> >> > investment of some amount of resources. Some other programs and users wouldn't >> >> > have such special information, and/or resource to invest for such >> >> > optimizations. For them, some amount of benefit would be helpful enough even >> >> > though its sub-optimal. >> >> > >> >> > I think we should help both groups, and DAMOS could be useful for the second >> >> > group. And I don't think DAMOS is useless for the first group. They could use >> >> > their information-based policy in prallel to DAMOS in some cases. E.g., if >> >> > they have a way to predict the data access pattern of specific memory region >> >> > even without help from DAMON, they can use their own policy for the region but >> >> > DAMOS for other regions. >> >> > >> >> > Someone could ask why not implement a user-space implementation for the second >> >> > group, then. First of all, DAMOS is not only for the user-space driven virtual >> >> > memory management optimization, but also for kernel-space programs and any >> >> > DAMOS-supportable address spaces including the physical address space. And, >> >> > another important goal of DAMOS for user space driven use case in addition to >> >> > reducing the redundant code is minimizing the user-kernel context switch >> >> > overhead for passing the monitoring results information and memory management >> >> > action requests. >> >> > >> >> > In summary, I agree the user space per-application policy daemon will be useful >> >> > for the specialized ultimate optimizations, but we also need DAMOS for another >> >> > common group of cases. >> >> > >> >> > If I'm missing something, please feel free to let me know. >> >> >> >> I guess that most end-users and quite some system administrators of >> >> small companies have no enough capability to take advantage of the >> >> per-application optimizations. How do they know the appropriate region >> >> number and proactive reclaim threshold? >> >> >> >> So per my understanding, Linux kernel >> >> need provide, >> >> >> >> 1. An in-kernel general policy that is obviously correct and benefits >> >> almost all users and applications, at least no regression. No >> >> complex configuration or deep knowledge is needed to take advantage >> >> of it. >> >> >> >> 2. Some way to inspect and control system and application behavior, so >> >> that some advanced and customized user space policy daemons can be >> >> built to satisfy some advanced users who have the enough knowledge >> >> for the applications and systems, for example, oomd. >> > >> > Agreed, and I think that's the approach that DAMON is currently taking. In >> > specific, we provide DAMON debugfs interface for users who want to inspect and >> > control their system and application behavior. Using it, we also made a PoC >> > level user space policy daemon[1]. >> > >> > For the in-kernel policies, we are developing DAMON-based kernel components one >> > by one, for specific usages. DAMON-based proactive reclamation module >> > (DAMON_RECLAIM) is one such example. Such DAMON-based components will remove >> > complex tunables that necessary for the general inspection and control of the >> > system but unnecessary for their specific purpose (e.g., proactive reclamation) >> > to allow users use it in a simple manner. Also, those will use conservative >> > default configs to not incur visible regression. For example, DAMON_RECLAIM >> > uses only up to 1% of single CPU time for the reclamation by default. >> >> I don't think DAMON schemes are the in-kernel general policy I mentioned >> above (1.). For example, NUMA balancing is a general policy to optimize >> performance. It tries to provide a general policy that works for all >> users with as few as possible tunables. If some tunables are needed, >> they will be provided as ABI. > > Exactly. What I'm saying is, DAMON schemes that exposed to user space via the > debugfs interface is for inspection of system and development of user space > daemon (2.). It requires some level of tuning and doesn't provide stable ABI > but the debugfs interface. Meanwhile, DAMON-based kernel components like > DAMON_RECLAIM can be used for the in-kernel general policy (1.). For example, > DAMON_RECLAIM also tries to be beneficial or at least incur no regression for > almost every users, provides as few as possible tunables, and provides those > via its ABI (module parameters), not debugfs. Thanks for your detailed explanation. Per my understanding, DAMON schemes are kind of building blocks of some kernel feature such as DAMON_RECLAIM. Whether do we need a new scheme depends on whether it's useful as part of some kernel feature. Do you agree? Best Regards, Huang, Ying > Thanks, > SJ > >> >> Best Regards, >> Huang, Ying >> >> > In short, I think we're on the same page, and adding DEMOTION scheme action >> > could be helpful for the users who want to efficiently inspect and control the >> > system/application behavior for their tiered memory systems. It's unclear how >> > much benefit this could give to users, though. I assume Baolin would come back >> > with some sort of numbers in the next spin. Nevertheless, I personally don't >> > think that's a critical blocker, as this patch is essentially just adding a way >> > for using the pre-existing primitive, namely move_pages(), in a little bit more >> > efficient manner, for the access pattern-based use cases. >> > >> > If I'm missing something, please feel free to let me know. >> > >> > [1] https://github.com/awslabs/damoos >> > >> > >> > Thanks, >> > SJ >> > >> >> >> >> Best Regards, >> >> Huang, Ying >>
On Thu, 30 Dec 2021 11:16:15 +0800 "Huang, Ying" <ying.huang@intel.com> wrote: > SeongJae Park <sj@kernel.org> writes: > > > On Wed, 29 Dec 2021 09:33:56 +0800 "Huang, Ying" <ying.huang@intel.com> wrote: > > > >> SeongJae Park <sj@kernel.org> writes: > >> > >> > Hello, > >> > > >> > On Mon, 27 Dec 2021 11:09:56 +0800 "Huang, Ying" <ying.huang@intel.com> wrote: > >> > > >> >> Hi, SeongJae, > >> >> > >> >> SeongJae Park <sj@kernel.org> writes: > >> >> > >> >> > Hi, > >> >> > > >> >> > On Thu, 23 Dec 2021 15:51:18 +0800 "Huang, Ying" <ying.huang@intel.com> wrote: > >> >> > >> >> [snip] > >> >> > >> >> >> It's good to avoid to change the source code of an application to apply > >> >> >> some memory management optimization (for example, use DAMON + > >> >> >> madvise()). But it's much easier to run a user space daemon to optimize > >> >> >> for the application. (for example, use DAMON + other information + > >> >> >> process_madvise()). > >> >> >> > >> >> >> And this kind of per-application optimization is kind of application > >> >> >> specific policy. This kind of policy may be too complex and flexible to > >> >> >> be put in the kernel directly. For example, in addition to DAMON, some > >> >> >> other application specific or system knowledge may be helpful too, so we > >> >> >> have process_madvise() for that before DAMON. Some more complex > >> >> >> algorithm may be needed for some applications. > >> >> >> > >> >> >> And this kind of application specific policy usually need complex > >> >> >> configuration. It's hard to export all these policy parameters to the > >> >> >> user space as the kernel ABI. Now, DAMON schemes parameters are > >> >> >> exported in debugfs so they are not considered ABI. So they may be > >> >> >> changed at any time. But applications need some stable and > >> >> >> well-maintained ABI. > >> >> >> > >> >> >> All in all, IMHO, what we need is a user space per-application policy > >> >> >> daemon with the information from DAMON and other sources. > >> >> > > >> >> > I basically agree to Ying, as I also noted in the coverletter of DAMOS > >> >> > patchset[1]: > >> >> > > >> >> > DAMON[1] can be used as a primitive for data access aware memory > >> >> > management optimizations. For that, users who want such optimizations > >> >> > should run DAMON, read the monitoring results, analyze it, plan a new > >> >> > memory management scheme, and apply the new scheme by themselves. Such > >> >> > efforts will be inevitable for some complicated optimizations. > >> >> > > >> >> > [1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=fda504fade7f124858d7022341dc46ff35b45274 > >> >> > > >> >> > That is, I believe some programs and big companies would definitely have their > >> >> > own information and want such kind of complicated optimizations. But, such > >> >> > optimizations would depend on characteristics of each program and require > >> >> > investment of some amount of resources. Some other programs and users wouldn't > >> >> > have such special information, and/or resource to invest for such > >> >> > optimizations. For them, some amount of benefit would be helpful enough even > >> >> > though its sub-optimal. > >> >> > > >> >> > I think we should help both groups, and DAMOS could be useful for the second > >> >> > group. And I don't think DAMOS is useless for the first group. They could use > >> >> > their information-based policy in prallel to DAMOS in some cases. E.g., if > >> >> > they have a way to predict the data access pattern of specific memory region > >> >> > even without help from DAMON, they can use their own policy for the region but > >> >> > DAMOS for other regions. > >> >> > > >> >> > Someone could ask why not implement a user-space implementation for the second > >> >> > group, then. First of all, DAMOS is not only for the user-space driven virtual > >> >> > memory management optimization, but also for kernel-space programs and any > >> >> > DAMOS-supportable address spaces including the physical address space. And, > >> >> > another important goal of DAMOS for user space driven use case in addition to > >> >> > reducing the redundant code is minimizing the user-kernel context switch > >> >> > overhead for passing the monitoring results information and memory management > >> >> > action requests. > >> >> > > >> >> > In summary, I agree the user space per-application policy daemon will be useful > >> >> > for the specialized ultimate optimizations, but we also need DAMOS for another > >> >> > common group of cases. > >> >> > > >> >> > If I'm missing something, please feel free to let me know. > >> >> > >> >> I guess that most end-users and quite some system administrators of > >> >> small companies have no enough capability to take advantage of the > >> >> per-application optimizations. How do they know the appropriate region > >> >> number and proactive reclaim threshold? > >> >> > >> >> So per my understanding, Linux kernel > >> >> need provide, > >> >> > >> >> 1. An in-kernel general policy that is obviously correct and benefits > >> >> almost all users and applications, at least no regression. No > >> >> complex configuration or deep knowledge is needed to take advantage > >> >> of it. > >> >> > >> >> 2. Some way to inspect and control system and application behavior, so > >> >> that some advanced and customized user space policy daemons can be > >> >> built to satisfy some advanced users who have the enough knowledge > >> >> for the applications and systems, for example, oomd. > >> > > >> > Agreed, and I think that's the approach that DAMON is currently taking. In > >> > specific, we provide DAMON debugfs interface for users who want to inspect and > >> > control their system and application behavior. Using it, we also made a PoC > >> > level user space policy daemon[1]. > >> > > >> > For the in-kernel policies, we are developing DAMON-based kernel components one > >> > by one, for specific usages. DAMON-based proactive reclamation module > >> > (DAMON_RECLAIM) is one such example. Such DAMON-based components will remove > >> > complex tunables that necessary for the general inspection and control of the > >> > system but unnecessary for their specific purpose (e.g., proactive reclamation) > >> > to allow users use it in a simple manner. Also, those will use conservative > >> > default configs to not incur visible regression. For example, DAMON_RECLAIM > >> > uses only up to 1% of single CPU time for the reclamation by default. > >> > >> I don't think DAMON schemes are the in-kernel general policy I mentioned > >> above (1.). For example, NUMA balancing is a general policy to optimize > >> performance. It tries to provide a general policy that works for all > >> users with as few as possible tunables. If some tunables are needed, > >> they will be provided as ABI. > > > > Exactly. What I'm saying is, DAMON schemes that exposed to user space via the > > debugfs interface is for inspection of system and development of user space > > daemon (2.). It requires some level of tuning and doesn't provide stable ABI > > but the debugfs interface. Meanwhile, DAMON-based kernel components like > > DAMON_RECLAIM can be used for the in-kernel general policy (1.). For example, > > DAMON_RECLAIM also tries to be beneficial or at least incur no regression for > > almost every users, provides as few as possible tunables, and provides those > > via its ABI (module parameters), not debugfs. > > Thanks for your detailed explanation. > > Per my understanding, DAMON schemes are kind of building blocks of some > kernel feature such as DAMON_RECLAIM. I pretty sure you're perfectly understanding my point. > Whether do we need a new scheme depends on whether it's useful as part of > some kernel feature. Do you agree? Yes, agreed. Thanks, SJ > > Best Regards, > Huang, Ying > > > Thanks, > > SJ > > > >> > >> Best Regards, > >> Huang, Ying > >> > >> > In short, I think we're on the same page, and adding DEMOTION scheme action > >> > could be helpful for the users who want to efficiently inspect and control the > >> > system/application behavior for their tiered memory systems. It's unclear how > >> > much benefit this could give to users, though. I assume Baolin would come back > >> > with some sort of numbers in the next spin. Nevertheless, I personally don't > >> > think that's a critical blocker, as this patch is essentially just adding a way > >> > for using the pre-existing primitive, namely move_pages(), in a little bit more > >> > efficient manner, for the access pattern-based use cases. > >> > > >> > If I'm missing something, please feel free to let me know. > >> > > >> > [1] https://github.com/awslabs/damoos > >> > > >> > > >> > Thanks, > >> > SJ > >> > > >> >> > >> >> Best Regards, > >> >> Huang, Ying > >>
On 12/28/2021 4:44 PM, SeongJae Park wrote: > Hello, > > On Mon, 27 Dec 2021 11:09:56 +0800 "Huang, Ying" <ying.huang@intel.com> wrote: > >> Hi, SeongJae, >> >> SeongJae Park <sj@kernel.org> writes: >> >>> Hi, >>> >>> On Thu, 23 Dec 2021 15:51:18 +0800 "Huang, Ying" <ying.huang@intel.com> wrote: >> >> [snip] >> >>>> It's good to avoid to change the source code of an application to apply >>>> some memory management optimization (for example, use DAMON + >>>> madvise()). But it's much easier to run a user space daemon to optimize >>>> for the application. (for example, use DAMON + other information + >>>> process_madvise()). >>>> >>>> And this kind of per-application optimization is kind of application >>>> specific policy. This kind of policy may be too complex and flexible to >>>> be put in the kernel directly. For example, in addition to DAMON, some >>>> other application specific or system knowledge may be helpful too, so we >>>> have process_madvise() for that before DAMON. Some more complex >>>> algorithm may be needed for some applications. >>>> >>>> And this kind of application specific policy usually need complex >>>> configuration. It's hard to export all these policy parameters to the >>>> user space as the kernel ABI. Now, DAMON schemes parameters are >>>> exported in debugfs so they are not considered ABI. So they may be >>>> changed at any time. But applications need some stable and >>>> well-maintained ABI. >>>> >>>> All in all, IMHO, what we need is a user space per-application policy >>>> daemon with the information from DAMON and other sources. >>> >>> I basically agree to Ying, as I also noted in the coverletter of DAMOS >>> patchset[1]: >>> >>> DAMON[1] can be used as a primitive for data access aware memory >>> management optimizations. For that, users who want such optimizations >>> should run DAMON, read the monitoring results, analyze it, plan a new >>> memory management scheme, and apply the new scheme by themselves. Such >>> efforts will be inevitable for some complicated optimizations. >>> >>> [1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=fda504fade7f124858d7022341dc46ff35b45274 >>> >>> That is, I believe some programs and big companies would definitely have their >>> own information and want such kind of complicated optimizations. But, such >>> optimizations would depend on characteristics of each program and require >>> investment of some amount of resources. Some other programs and users wouldn't >>> have such special information, and/or resource to invest for such >>> optimizations. For them, some amount of benefit would be helpful enough even >>> though its sub-optimal. >>> >>> I think we should help both groups, and DAMOS could be useful for the second >>> group. And I don't think DAMOS is useless for the first group. They could use >>> their information-based policy in prallel to DAMOS in some cases. E.g., if >>> they have a way to predict the data access pattern of specific memory region >>> even without help from DAMON, they can use their own policy for the region but >>> DAMOS for other regions. >>> >>> Someone could ask why not implement a user-space implementation for the second >>> group, then. First of all, DAMOS is not only for the user-space driven virtual >>> memory management optimization, but also for kernel-space programs and any >>> DAMOS-supportable address spaces including the physical address space. And, >>> another important goal of DAMOS for user space driven use case in addition to >>> reducing the redundant code is minimizing the user-kernel context switch >>> overhead for passing the monitoring results information and memory management >>> action requests. >>> >>> In summary, I agree the user space per-application policy daemon will be useful >>> for the specialized ultimate optimizations, but we also need DAMOS for another >>> common group of cases. >>> >>> If I'm missing something, please feel free to let me know. >> >> I guess that most end-users and quite some system administrators of >> small companies have no enough capability to take advantage of the >> per-application optimizations. How do they know the appropriate region >> number and proactive reclaim threshold? >> >> So per my understanding, Linux kernel >> need provide, >> >> 1. An in-kernel general policy that is obviously correct and benefits >> almost all users and applications, at least no regression. No >> complex configuration or deep knowledge is needed to take advantage >> of it. >> >> 2. Some way to inspect and control system and application behavior, so >> that some advanced and customized user space policy daemons can be >> built to satisfy some advanced users who have the enough knowledge >> for the applications and systems, for example, oomd. > > Agreed, and I think that's the approach that DAMON is currently taking. In > specific, we provide DAMON debugfs interface for users who want to inspect and > control their system and application behavior. Using it, we also made a PoC > level user space policy daemon[1]. > > For the in-kernel policies, we are developing DAMON-based kernel components one > by one, for specific usages. DAMON-based proactive reclamation module > (DAMON_RECLAIM) is one such example. Such DAMON-based components will remove > complex tunables that necessary for the general inspection and control of the > system but unnecessary for their specific purpose (e.g., proactive reclamation) > to allow users use it in a simple manner. Also, those will use conservative > default configs to not incur visible regression. For example, DAMON_RECLAIM > uses only up to 1% of single CPU time for the reclamation by default. > > In short, I think we're on the same page, and adding DEMOTION scheme action > could be helpful for the users who want to efficiently inspect and control the > system/application behavior for their tiered memory systems. It's unclear how Agree. It will be easier for us to deploy it to the products for the common scenarios. > much benefit this could give to users, though. I assume Baolin would come back > with some sort of numbers in the next spin. Nevertheless, I personally don't Yes, I am still trying to set up the effective measurement environment and get the performance number in the next version. > think that's a critical blocker, as this patch is essentially just adding a way > for using the pre-existing primitive, namely move_pages(), in a little bit more > efficient manner, for the access pattern-based use cases. > > If I'm missing something, please feel free to let me know. > > [1] https://github.com/awslabs/damoos
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