include/linux/stackdepot.h | 72 ++++++++++++++++++++ lib/stackdepot.c | 97 ++++++++++++++------------ mm/page_owner.c | 136 +++++++++++++++++++++++++++++++++++++ 3 files changed, 262 insertions(+), 43 deletions(-)
Changes v6 -> v7:
- Rebased on top of Andrey Konovalov's libstackdepot patchset
- Reformulated the changelogs
Changes v5 -> v6:
- Rebase on top of v6.7-rc1
- Move stack_record struct to the header
- Addressed feedback from Vlastimil
(some code tweaks and changelogs suggestions)
Changes v4 -> v5:
- Addressed feedback from Alexander Potapenko
Changes v3 -> v4:
- Rebase (long time has passed)
- Use boolean instead of enum for action by Alexander Potapenko
- (I left some feedback untouched because it's been long and
would like to discuss it here now instead of re-vamping
and old thread)
Changes v2 -> v3:
- Replace interface in favor of seq operations
(suggested by Vlastimil)
- Use debugfs interface to store/read valued (suggested by Ammar)
page_owner is a great debug functionality tool that lets us know
about all pages that have been allocated/freed and their specific
stacktrace.
This comes very handy when debugging memory leaks, since with
some scripting we can see the outstanding allocations, which might point
to a memory leak.
In my experience, that is one of the most useful cases, but it can get
really tedious to screen through all pages and try to reconstruct the
stack <-> allocated/freed relationship, becoming most of the time a
daunting and slow process when we have tons of allocation/free operations.
This patchset aims to ease that by adding a new functionality into
page_owner.
This functionality creates a new read-only file called "page_owner_stacks",
which prints out all the stacks followed by their outstanding number
of allocations (being that the times the stacktrace has allocated
but not freed yet).
This gives us a clear and a quick overview of stacks <-> allocated/free.
We take advantage of the new refcount_f field that stack_record struct
gained, and increment/decrement the stack refcount on every
__set_page_owner() (alloc operation) and __reset_page_owner (free operation)
call.
Unfortunately, we cannot use the new stackdepot api
STACK_DEPOT_FLAG_{GET,PUT} because it does not fulfill page_owner needs,
meaning we would have to special case things, at which point
makes more sense for page_owner to do its own {dec,inc}rementing
of the stacks.
E.g: Using STACK_DEPOT_FLAG_PUT, once the refcount reaches 0,
such stack gets evicted, so page_owner would lose information.
This patch also creates a new file called 'page_owner_threshold'.
By writing a value to it, the stacks which refcount is below such
value will be filtered out.
In order to better exercise the path in stack_depot_get_next_stack(),
I artificially filled the buckets with more than one stack, making sure
I was getting all of then when reading from it.
On a side note, stack_depot_get_next_stack() could be somehow reconstructed
to be in page_owner code, but we would have to move stack_table
into the header, so page_owner can access it.
I can do that if that's preferred, so stackdepot.c would not get "poluted".
A PoC can be found below:
# cat /sys/kernel/debug/page_owner_stacks > page_owner_full_stacks.txt
# head -40 page_owner_full_stacks.txt
prep_new_page+0xa9/0x120
get_page_from_freelist+0x801/0x2210
__alloc_pages+0x18b/0x350
alloc_pages_mpol+0x91/0x1f0
folio_alloc+0x14/0x50
filemap_alloc_folio+0xb2/0x100
page_cache_ra_unbounded+0x96/0x180
filemap_get_pages+0xfd/0x590
filemap_read+0xcc/0x330
blkdev_read_iter+0xb8/0x150
vfs_read+0x285/0x320
ksys_read+0xa5/0xe0
do_syscall_64+0x80/0x160
entry_SYSCALL_64_after_hwframe+0x6e/0x76
stack_count: 521
prep_new_page+0xa9/0x120
get_page_from_freelist+0x801/0x2210
__alloc_pages+0x18b/0x350
alloc_pages_mpol+0x91/0x1f0
folio_alloc+0x14/0x50
filemap_alloc_folio+0xb2/0x100
__filemap_get_folio+0x14a/0x490
ext4_write_begin+0xbd/0x4b0 [ext4]
generic_perform_write+0xc1/0x1e0
ext4_buffered_write_iter+0x68/0xe0 [ext4]
ext4_file_write_iter+0x70/0x740 [ext4]
vfs_write+0x33d/0x420
ksys_write+0xa5/0xe0
do_syscall_64+0x80/0x160
entry_SYSCALL_64_after_hwframe+0x6e/0x76
stack_count: 4609
...
...
# echo 5000 > /sys/kernel/debug/page_owner_threshold
# cat /sys/kernel/debug/page_owner_stacks > page_owner_full_stacks_5000.txt
# head -40 page_owner_full_stacks_5000.txt
prep_new_page+0xa9/0x120
get_page_from_freelist+0x801/0x2210
__alloc_pages+0x18b/0x350
alloc_pages_mpol+0x91/0x1f0
folio_alloc+0x14/0x50
filemap_alloc_folio+0xb2/0x100
__filemap_get_folio+0x14a/0x490
ext4_write_begin+0xbd/0x4b0 [ext4]
generic_perform_write+0xc1/0x1e0
ext4_buffered_write_iter+0x68/0xe0 [ext4]
ext4_file_write_iter+0x70/0x740 [ext4]
vfs_write+0x33d/0x420
ksys_pwrite64+0x75/0x90
do_syscall_64+0x80/0x160
entry_SYSCALL_64_after_hwframe+0x6e/0x76
stack_count: 6781
prep_new_page+0xa9/0x120
get_page_from_freelist+0x801/0x2210
__alloc_pages+0x18b/0x350
pcpu_populate_chunk+0xec/0x350
pcpu_balance_workfn+0x2d1/0x4a0
process_scheduled_works+0x84/0x380
worker_thread+0x12a/0x2a0
kthread+0xe3/0x110
ret_from_fork+0x30/0x50
ret_from_fork_asm+0x1b/0x30
stack_count: 8641
Oscar Salvador (4):
lib/stackdepot: Move stack_record struct definition into the header
mm,page_owner: Implement the tracking of the stacks count
mm,page_owner: Display all stacks and their count
mm,page_owner: Filter out stacks by a threshold
include/linux/stackdepot.h | 72 ++++++++++++++++++++
lib/stackdepot.c | 97 ++++++++++++++------------
mm/page_owner.c | 136 +++++++++++++++++++++++++++++++++++++
3 files changed, 262 insertions(+), 43 deletions(-)
--
2.43.0
On Fri, 9 Feb 2024 at 00:45, Oscar Salvador <osalvador@suse.de> wrote: > > Changes v6 -> v7: > - Rebased on top of Andrey Konovalov's libstackdepot patchset > - Reformulated the changelogs Overall looks fine, but I think it's not rebased against the latest stackdepot version in -next. That version re-introduces variable-sized records and there's some trickery required so you do not end up with refcount warnings.
On Fri, Feb 09, 2024 at 09:03:21AM +0100, Marco Elver wrote: > On Fri, 9 Feb 2024 at 00:45, Oscar Salvador <osalvador@suse.de> wrote: > > > > Changes v6 -> v7: > > - Rebased on top of Andrey Konovalov's libstackdepot patchset > > - Reformulated the changelogs > > Overall looks fine, but I think it's not rebased against the latest > stackdepot version in -next. That version re-introduces variable-sized > records and there's some trickery required so you do not end up with > refcount warnings. Thanks a lot Marco for having a look and for the feedback, that's highly appreciated. -- Oscar Salvador SUSE Labs
On Fri, 9 Feb 2024 00:45:35 +0100 Oscar Salvador <osalvador@suse.de> wrote:
> page_owner is a great debug functionality tool that lets us know
> about all pages that have been allocated/freed and their specific
> stacktrace.
> This comes very handy when debugging memory leaks, since with
> some scripting we can see the outstanding allocations, which might point
> to a memory leak.
>
> In my experience, that is one of the most useful cases, but it can get
> really tedious to screen through all pages and try to reconstruct the
> stack <-> allocated/freed relationship, becoming most of the time a
> daunting and slow process when we have tons of allocation/free operations.
>
> This patchset aims to ease that by adding a new functionality into
> page_owner.
> This functionality creates a new read-only file called "page_owner_stacks",
The full path would be appreciated.
> which prints out all the stacks followed by their outstanding number
> of allocations (being that the times the stacktrace has allocated
> but not freed yet).
> This gives us a clear and a quick overview of stacks <-> allocated/free.
>
> We take advantage of the new refcount_f field that stack_record struct
> gained, and increment/decrement the stack refcount on every
> __set_page_owner() (alloc operation) and __reset_page_owner (free operation)
> call.
>
> Unfortunately, we cannot use the new stackdepot api
> STACK_DEPOT_FLAG_{GET,PUT} because it does not fulfill page_owner needs,
> meaning we would have to special case things, at which point
> makes more sense for page_owner to do its own {dec,inc}rementing
> of the stacks.
> E.g: Using STACK_DEPOT_FLAG_PUT, once the refcount reaches 0,
> such stack gets evicted, so page_owner would lose information.
>
> This patch also creates a new file called 'page_owner_threshold'.
> By writing a value to it, the stacks which refcount is below such
> value will be filtered out.
>
> In order to better exercise the path in stack_depot_get_next_stack(),
> I artificially filled the buckets with more than one stack, making sure
> I was getting all of then when reading from it.
>
> On a side note, stack_depot_get_next_stack() could be somehow reconstructed
> to be in page_owner code, but we would have to move stack_table
> into the header, so page_owner can access it.
> I can do that if that's preferred, so stackdepot.c would not get "poluted".
>
> A PoC can be found below:
>
> # cat /sys/kernel/debug/page_owner_stacks > page_owner_full_stacks.txt
Oh, there it is. I wonder why we didn't use /sys/kernel/mm/
Would a new /sys/kernel/debug/page_owner_something/ be a good idea? We
might add more things later. Then it can be
/sys/kernel/debug/page_owner_something/full_stacks.
/sys/kernel/debug/page_owner/ would be nice, but it's too late for
that.
> Oscar Salvador (4):
> lib/stackdepot: Move stack_record struct definition into the header
> mm,page_owner: Implement the tracking of the stacks count
> mm,page_owner: Display all stacks and their count
> mm,page_owner: Filter out stacks by a threshold
>
> include/linux/stackdepot.h | 72 ++++++++++++++++++++
> lib/stackdepot.c | 97 ++++++++++++++------------
> mm/page_owner.c | 136 +++++++++++++++++++++++++++++++++++++
> 3 files changed, 262 insertions(+), 43 deletions(-)
Documentation/mm/page_owner.rst?
On Thu, Feb 08, 2024 at 04:28:18PM -0800, Andrew Morton wrote: > Oh, there it is. I wonder why we didn't use /sys/kernel/mm/ I just followed the convention we use at the moment, which happens to be /sys/kernel/debug/page_owner_xxx. > Would a new /sys/kernel/debug/page_owner_something/ be a good idea? We > might add more things later. Then it can be > /sys/kernel/debug/page_owner_something/full_stacks. > /sys/kernel/debug/page_owner/ would be nice, but it's too late for > that. Well, we could certainly do that, so we do not scatter the files in /sys/kernel/debug/ but rather gather them in pagE_owner directory. Let me see if I can come up with a proper name. > > Oscar Salvador (4): > > lib/stackdepot: Move stack_record struct definition into the header > > mm,page_owner: Implement the tracking of the stacks count > > mm,page_owner: Display all stacks and their count > > mm,page_owner: Filter out stacks by a threshold > > > > include/linux/stackdepot.h | 72 ++++++++++++++++++++ > > lib/stackdepot.c | 97 ++++++++++++++------------ > > mm/page_owner.c | 136 +++++++++++++++++++++++++++++++++++++ > > 3 files changed, 262 insertions(+), 43 deletions(-) > > Documentation/mm/page_owner.rst? Heh, we are definitely going to need some documentation. Let me prepare something. Thanks Andrew -- Oscar Salvador SUSE Labs
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