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

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Message-ID: <19f0b0bb-dd2d-4cdd-8b86-b995b01bfd03@oracle.com>
Date: Tue, 5 Nov 2024 23:07:07 +0000
From: Alan Maguire <alan.maguire@...cle.com>
To: Florian Schmaus <flo@...kplace.eu>,
        Masahiro Yamada
 <masahiroy@...nel.org>,
        Holger Hoffstätte
 <holger@...lied-asynchrony.com>
Cc: Nathan Chancellor <nathan@...nel.org>, Nicolas Schier
 <nicolas@...sle.eu>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Martin KaFai Lau <martin.lau@...ux.dev>,
        Eduard Zingerman
 <eddyz87@...il.com>, Song Liu <song@...nel.org>,
        Yonghong Song <yonghong.song@...ux.dev>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...nel.org>, Stanislav Fomichev <sdf@...ichev.me>,
        Hao Luo <haoluo@...gle.com>, Jiri Olsa <jolsa@...nel.org>,
        bpf@...r.kernel.org, linux-kbuild@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Arnaldo Carvalho de Melo <acme@...nel.org>
Subject: Re: [PATCH] kbuild,bpf: pass make jobs' value to pahole

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@...lied-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@...kplace.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