kbuild,bpf: pass make jobs' value to pahole

[PATCH] kbuild,bpf: pass make jobs' value to pahole

Posted by Florian Schmaus 3 weeks, 1 day ago

Pass the value of make's -j/--jobs argument to pahole, to avoid out of
memory errors and make pahole respect the "jobs" value of make.

On systems with little memory but many cores, invoking pahole using -j
without argument potentially creates too many pahole instances,
causing an out-of-memory situation. Instead, we should pass make's
"jobs" value as an argument to pahole's -j, which is likely configured
to be (much) lower than the actual core count on such systems.

If make was invoked without -j, either via cmdline or MAKEFLAGS, then
JOBS will be simply empty, resulting in the existing behavior, as
expected.

Signed-off-by: Florian Schmaus <flo@geekplace.eu>
---
 scripts/Makefile.btf | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/scripts/Makefile.btf b/scripts/Makefile.btf
index b75f09f3f424..c3cbeb13de50 100644
--- a/scripts/Makefile.btf
+++ b/scripts/Makefile.btf
@@ -3,6 +3,8 @@
 pahole-ver := $(CONFIG_PAHOLE_VERSION)
 pahole-flags-y :=
 
+JOBS := $(patsubst -j%,%,$(filter -j%,$(MAKEFLAGS)))
+
 ifeq ($(call test-le, $(pahole-ver), 125),y)
 
 # pahole 1.18 through 1.21 can't handle zero-sized per-CPU vars
@@ -12,14 +14,14 @@ endif
 
 pahole-flags-$(call test-ge, $(pahole-ver), 121)	+= --btf_gen_floats
 
-pahole-flags-$(call test-ge, $(pahole-ver), 122)	+= -j
+pahole-flags-$(call test-ge, $(pahole-ver), 122)	+= -j$(JOBS)
 
 pahole-flags-$(call test-ge, $(pahole-ver), 125)	+= --skip_encoding_btf_inconsistent_proto --btf_gen_optimized
 
 else
 
 # Switch to using --btf_features for v1.26 and later.
-pahole-flags-$(call test-ge, $(pahole-ver), 126)  = -j --btf_features=encode_force,var,float,enum64,decl_tag,type_tag,optimized_func,consistent_func,decl_tag_kfuncs
+pahole-flags-$(call test-ge, $(pahole-ver), 126)  = -j$(JOBS) --btf_features=encode_force,var,float,enum64,decl_tag,type_tag,optimized_func,consistent_func,decl_tag_kfuncs
 
 ifneq ($(KBUILD_EXTMOD),)
 module-pahole-flags-$(call test-ge, $(pahole-ver), 126) += --btf_features=distilled_base
-- 
2.45.2

Re: [PATCH] kbuild,bpf: pass make jobs' value to pahole

Posted by Holger Hoffstätte 3 weeks ago

On 2024-11-02 11:04, Florian Schmaus wrote:
> Pass the value of make's -j/--jobs argument to pahole, to avoid out of
> memory errors and make pahole respect the "jobs" value of make.
> 
> On systems with little memory but many cores, invoking pahole using -j
> without argument potentially creates too many pahole instances,
> causing an out-of-memory situation. Instead, we should pass make's
> "jobs" value as an argument to pahole's -j, which is likely configured
> to be (much) lower than the actual core count on such systems.
> 
> If make was invoked without -j, either via cmdline or MAKEFLAGS, then
> JOBS will be simply empty, resulting in the existing behavior, as
> expected.
> 
> Signed-off-by: Florian Schmaus <flo@geekplace.eu>

As discussed on IRC:

Tested-by: Holger Hoffstätte <holger@applied-asynchrony.com>

Thanks!
Holger

Re: [PATCH] kbuild,bpf: pass make jobs' value to pahole

Posted by Masahiro Yamada 3 weeks ago

On Sun, Nov 3, 2024 at 9:04 PM Holger Hoffstätte
<holger@applied-asynchrony.com> wrote:
>
> On 2024-11-02 11:04, Florian Schmaus wrote:
> > Pass the value of make's -j/--jobs argument to pahole, to avoid out of
> > memory errors and make pahole respect the "jobs" value of make.
> >
> > On systems with little memory but many cores, invoking pahole using -j
> > without argument potentially creates too many pahole instances,
> > causing an out-of-memory situation. Instead, we should pass make's
> > "jobs" value as an argument to pahole's -j, which is likely configured
> > to be (much) lower than the actual core count on such systems.
> >
> > If make was invoked without -j, either via cmdline or MAKEFLAGS, then
> > JOBS will be simply empty, resulting in the existing behavior, as
> > expected.
> >
> > Signed-off-by: Florian Schmaus <flo@geekplace.eu>
>
> As discussed on IRC:

Do not do this. Others do not see what was discussed.




I guess the right thing to do is to join the jobserver.

https://www.gnu.org/software/make/manual/html_node/POSIX-Jobserver.html




-- 
Best Regards
Masahiro Yamada

Re: [PATCH] kbuild,bpf: pass make jobs' value to pahole

Posted by Florian Schmaus 2 weeks, 6 days ago

On 03/11/2024 14.22, Masahiro Yamada wrote:
> On Sun, Nov 3, 2024 at 9:04 PM Holger Hoffstätte
> <holger@applied-asynchrony.com> wrote:
>>
>> On 2024-11-02 11:04, Florian Schmaus wrote:
>>> Pass the value of make's -j/--jobs argument to pahole, to avoid out of
>>> memory errors and make pahole respect the "jobs" value of make.
>>>
>>> On systems with little memory but many cores, invoking pahole using -j
>>> without argument potentially creates too many pahole instances,
>>> causing an out-of-memory situation. Instead, we should pass make's
>>> "jobs" value as an argument to pahole's -j, which is likely configured
>>> to be (much) lower than the actual core count on such systems.
>>>
>>> If make was invoked without -j, either via cmdline or MAKEFLAGS, then
>>> JOBS will be simply empty, resulting in the existing behavior, as
>>> expected.
>>>
>>> Signed-off-by: Florian Schmaus <flo@geekplace.eu>
>>
>> As discussed on IRC:
> 
> Do not do this. Others do not see what was discussed.

Sorry, you are right. However, not much was discussed. Holger just 
pointed out that the memory usage of pahole was already reported as 
problematic in

https://lore.kernel.org/lkml/20240820085950.200358-1-jirislaby@kernel.org/

My patch would potentially help there as well, as it allows the user to 
limit the number of threads used by pahole.


> I guess the right thing to do is to join the jobserver.
> 
> https://www.gnu.org/software/make/manual/html_node/POSIX-Jobserver.html

Yes, this would be the ideal solution. Until it is implemented, the 
proposed patch is probably the next best thing.

- Florian

Re: [PATCH] kbuild,bpf: pass make jobs' value to pahole

Posted by Alan Maguire 2 weeks, 4 days ago

On 04/11/2024 12:52, Florian Schmaus wrote:
> On 03/11/2024 14.22, Masahiro Yamada wrote:
>> On Sun, Nov 3, 2024 at 9:04 PM Holger Hoffstätte
>> <holger@applied-asynchrony.com> wrote:
>>>
>>> On 2024-11-02 11:04, Florian Schmaus wrote:
>>>> Pass the value of make's -j/--jobs argument to pahole, to avoid out of
>>>> memory errors and make pahole respect the "jobs" value of make.
>>>>
>>>> On systems with little memory but many cores, invoking pahole using -j
>>>> without argument potentially creates too many pahole instances,
>>>> causing an out-of-memory situation. Instead, we should pass make's
>>>> "jobs" value as an argument to pahole's -j, which is likely configured
>>>> to be (much) lower than the actual core count on such systems.
>>>>
>>>> If make was invoked without -j, either via cmdline or MAKEFLAGS, then
>>>> JOBS will be simply empty, resulting in the existing behavior, as
>>>> expected.
>>>>
>>>> Signed-off-by: Florian Schmaus <flo@geekplace.eu>
>>>
>>> As discussed on IRC:
>>
>> Do not do this. Others do not see what was discussed.
> 
> Sorry, you are right. However, not much was discussed. Holger just
> pointed out that the memory usage of pahole was already reported as
> problematic in
> 
> https://lore.kernel.org/lkml/20240820085950.200358-1-jirislaby@kernel.org/
> 
> My patch would potentially help there as well, as it allows the user to
> limit the number of threads used by pahole.
> 
> 
>> I guess the right thing to do is to join the jobserver.
>>
>> https://www.gnu.org/software/make/manual/html_node/POSIX-Jobserver.html
> 
> Yes, this would be the ideal solution. Until it is implemented, the
> proposed patch is probably the next best thing.
> 
> - Florian
> 

If you haven't already, I'd suggest testing the latest pahole (building
from master branch). Significant improvements in memory utilization have
been made and more are planned post the 1.28 release.

In terms of the patch itself, respecting the "make -j" value seems right
to me. Thanks!

Alan