linux-kernel - Re: [linus:master] [mseal] 8be7258aad: stress-ng.pagemove.page_remaps_per

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Message-Id: <D38D6LJZOIQK.2GV58PGVL5K85@gmail.com>
Date: Tue, 06 Aug 2024 09:24:56 +1000
From: "Nicholas Piggin" <npiggin@...il.com>
To: "Linus Torvalds" <torvalds@...ux-foundation.org>, "Jeff Xu"
 <jeffxu@...gle.com>
Cc: "Michael Ellerman" <mpe@...erman.id.au>, "Christophe Leroy"
 <christophe.leroy@...roup.eu>, "Pedro Falcato" <pedro.falcato@...il.com>,
 "kernel test robot" <oliver.sang@...el.com>, "Jeff Xu"
 <jeffxu@...omium.org>, <oe-lkp@...ts.linux.dev>, <lkp@...el.com>,
 <linux-kernel@...r.kernel.org>, "Andrew Morton"
 <akpm@...ux-foundation.org>, "Kees Cook" <keescook@...omium.org>, "Liam R.
 Howlett" <Liam.Howlett@...cle.com>, "Dave Hansen" <dave.hansen@...el.com>,
 "Greg Kroah-Hartman" <gregkh@...uxfoundation.org>, "Guenter Roeck"
 <groeck@...omium.org>, "Jann Horn" <jannh@...gle.com>, "Jonathan Corbet"
 <corbet@....net>, "Jorge Lucangeli Obes" <jorgelo@...omium.org>, "Matthew
 Wilcox" <willy@...radead.org>, "Muhammad Usama Anjum"
 <usama.anjum@...labora.com>, Stephen Röttger
 <sroettger@...gle.com>, "Suren Baghdasaryan" <surenb@...gle.com>, "Amer Al
 Shanawany" <amer.shanawany@...il.com>, "Javier Carrasco"
 <javier.carrasco.cruz@...il.com>, "Shuah Khan" <shuah@...nel.org>,
 <linux-api@...r.kernel.org>, <linux-mm@...ck.org>, <ying.huang@...el.com>,
 <feng.tang@...el.com>, <fengwei.yin@...el.com>
Subject: Re: [linus:master] [mseal] 8be7258aad:
 stress-ng.pagemove.page_remaps_per_sec -4.4% regression

On Tue Aug 6, 2024 at 5:48 AM AEST, Linus Torvalds wrote:
> On Mon, 5 Aug 2024 at 12:38, Jeff Xu <jeffxu@...gle.com> wrote:
> >
> > I'm curious, why does ppc need to unmap vdso ? ( other archs don't
> > have unmap logic.)
>
> I have no idea. There are comments about 'perf' getting confused about
> mmap counts when 'context.vdso' isn't set up.
>
> But x86 has the same context.vdso logic, and does *not* set the
> pointer before installing the vma, for example. Also does not zero it
> out on munmap(), although it does have the mremap logic.
>
> For all I know it may all be entirely unnecessary, and could be
> removed entirely.

I don't know much about vdso code, it predated my involvedment in ppc.
Commit 83d3f0e90c6c8 says CRIU (checkpoint restore in userspace) is
moving it around. Why CRIU wants to do that, I don't know.

Can userspace on other archs not unmap their vdsos?

Thanks,
Nick