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

From: Mel Gorman <mgorman@techsingularity.net>
To: Andrii Nakryiko <andrii.nakryiko@gmail.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
	Michal Suchanek <msuchanek@suse.de>,
	Alexei Starovoitov <ast@kernel.org>,
	Daniel Borkmann <daniel@iogearbox.net>,
	Martin KaFai Lau <kafai@fb.com>, Song Liu <songliubraving@fb.com>,
	Yonghong Song <yhs@fb.com>,
	John Fastabend <john.fastabend@gmail.com>,
	KP Singh <kpsingh@kernel.org>,
	open list <linux-kernel@vger.kernel.org>,
	Arnaldo Carvalho de Melo <acme@redhat.com>,
	Jiri Olsa <jolsa@kernel.org>, Hritik Vijay <hritikxx8@gmail.com>,
	bpf <bpf@vger.kernel.org>, Linux-Net <netdev@vger.kernel.org>,
	Linux-MM <linux-mm@kvack.org>
Subject: Re: [PATCH] mm/page_alloc: Work around a pahole limitation with zero-sized struct pagesets
Date: Wed, 26 May 2021 19:13:07 +0100	[thread overview]
Message-ID: <20210526181306.GZ30378@techsingularity.net> (raw)
In-Reply-To: <CAEf4BzZOQnBgYXSR71HgsqhYcaFk5M5mre+6do+hnuxgWx5aNg@mail.gmail.com>

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@suse.de>
> > Reported-by: Hritik Vijay <hritikxx8@gmail.com>
> > Debugged-by: Andrii Nakryiko <andrii.nakryiko@gmail.com>
> > Signed-off-by: Mel Gorman <mgorman@techsingularity.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@kernel.org>
> Tested-by: Andrii Nakryiko <andrii@kernel.org>
> 

Thanks!

-- 
Mel Gorman
SUSE Labs