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

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Date:   Sat, 29 May 2021 17:46:54 -0700
From:   Andrii Nakryiko <andrii.nakryiko@...il.com>
To:     David Laight <David.Laight@...lab.com>
Cc:     Christoph Hellwig <hch@...radead.org>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Arnaldo Carvalho de Melo <acme@...hat.com>,
        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>,
        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 Fri, May 28, 2021 at 1:09 AM David Laight <David.Laight@...lab.com> wrote:
>
> From: Andrii Nakryiko
> > Sent: 27 May 2021 15:42
> ...
> > I agree that empty structs are useful, but here we are talking about
> > per-CPU variables only, which is the first use case so far, as far as
> > I can see. If we had pahole 1.22 released and widely packaged it could
> > have been a viable option to force it on everyone.
> ...
>
> Would it be feasible to put the sources for pahole into the
> kernel repository and build it at the same time as objtool?
>
> That would remove any issues about the latest version
> not being available.

That would be great for the kernel build, but pahole is more than just
a DWARF-to-BTF converter and it has a substantial amount of logic for
loading and processing DWARF before it gets converted to BTF. All
BTF-related pieces are provided by libbpf, which is already part of
kernel sources, so that's not a problem. DWARF processing is a problem
and would add a new dependency on libdw-devel, at least.

>
>         David
>
> -
> Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
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