linux-kernel - Re: [PATCH] mm/page_alloc: Work around a pahole limitation with zero-sized struct pagesets

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Message-ID: <20210526181306.GZ30378@techsingularity.net>
Date:   Wed, 26 May 2021 19:13:07 +0100
From:   Mel Gorman <mgorman@...hsingularity.net>
To:     Andrii Nakryiko <andrii.nakryiko@...il.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Michal Suchanek <msuchanek@...e.de>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...nel.org>,
        open list <linux-kernel@...r.kernel.org>,
        Arnaldo Carvalho de Melo <acme@...hat.com>,
        Jiri Olsa <jolsa@...nel.org>,
        Hritik Vijay <hritikxx8@...il.com>, bpf <bpf@...r.kernel.org>,
        Linux-Net <netdev@...r.kernel.org>, Linux-MM <linux-mm@...ck.org>
Subject: Re: [PATCH] mm/page_alloc: Work around a pahole limitation with
 zero-sized struct pagesets

On Wed, May 26, 2021 at 09:57:31AM -0700, Andrii Nakryiko wrote:
> > This patch checks for older versions of pahole and forces struct pagesets
> > to be non-zero sized as a workaround when CONFIG_DEBUG_INFO_BTF is set. A
> > warning is omitted so that distributions can update pahole when 1.22
> 
> s/omitted/emitted/ ?
> 

Yes.

> > is released.
> >
> > Reported-by: Michal Suchanek <msuchanek@...e.de>
> > Reported-by: Hritik Vijay <hritikxx8@...il.com>
> > Debugged-by: Andrii Nakryiko <andrii.nakryiko@...il.com>
> > Signed-off-by: Mel Gorman <mgorman@...hsingularity.net>
> > ---
> 
> Looks good! I verified that this does fix the issue on the latest
> linux-next tree, thanks!
> 

Excellent

> One question, should
> 
> Fixes: 5716a627517d ("mm/page_alloc: convert per-cpu list protection
> to local_lock")
> 
> be added to facilitate backporting?
> 

The git commit is not stable because the patch "mm/page_alloc: convert
per-cpu list protection to local_lock" is in Andrew's mmotm tree which is
quilt based. I decided not to treat the patch as a fix because the patch is
not wrong as such, it's a limitation of an external tool.  However, I would
expect both the problematic patch and the BTF workaround to go in during
the same merge window so backports to -stable should not be required.

> Either way:
> 
> Acked-by: Andrii Nakryiko <andrii@...nel.org>
> Tested-by: Andrii Nakryiko <andrii@...nel.org>
> 

Thanks!

-- 
Mel Gorman
SUSE Labs