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

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Message-ID: <YK9j3YeMTZ+0I8NA@infradead.org>
Date:   Thu, 27 May 2021 10:18:21 +0100
From:   Christoph Hellwig <hch@...radead.org>
To:     Mel Gorman <mgorman@...hsingularity.net>
Cc:     Christoph Hellwig <hch@...radead.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Arnaldo Carvalho de Melo <acme@...hat.com>,
        Andrii Nakryiko <andrii.nakryiko@...il.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 Thu, May 27, 2021 at 10:04:22AM +0100, Mel Gorman wrote:
> What do you suggest as an alternative?
> 
> I added Arnaldo to the cc as he tagged the last released version of
> pahole (1.21) and may be able to tag a 1.22 with Andrii's fix for pahole
> included.
> 
> The most obvious alternative fix for this issue is to require pahole
> 1.22 to set CONFIG_DEBUG_INFO_BTF but obviously a version 1.22 that works
> needs to exist first and right now it does not. I'd be ok with this but
> users of DEBUG_INFO_BTF may object given that it'll be impossible to set
> the option until there is a release.

Yes, disable BTF.  Empty structs are a very useful feature that we use
in various places in the kernel.  We can't just keep piling hacks over
hacks to make that work with a recent fringe feature.