linux-kernel - Re: [RFC PATCH RESEND 00/28] per-VMA locks proposal

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Message-ID: <YxGz+3TT/J7u6H81@hirez.programming.kicks-ass.net>
Date:   Fri, 2 Sep 2022 09:42:51 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Suren Baghdasaryan <surenb@...gle.com>
Cc:     akpm@...ux-foundation.org, michel@...pinasse.org,
        jglisse@...gle.com, mhocko@...e.com, vbabka@...e.cz,
        hannes@...xchg.org, mgorman@...e.de, dave@...olabs.net,
        willy@...radead.org, liam.howlett@...cle.com,
        ldufour@...ux.ibm.com, laurent.dufour@...ibm.com,
        paulmck@...nel.org, luto@...nel.org, songliubraving@...com,
        peterx@...hat.com, david@...hat.com, dhowells@...hat.com,
        hughd@...gle.com, bigeasy@...utronix.de, kent.overstreet@...ux.dev,
        rientjes@...gle.com, axelrasmussen@...gle.com, joelaf@...gle.com,
        minchan@...gle.com, kernel-team@...roid.com, linux-mm@...ck.org,
        linux-arm-kernel@...ts.infradead.org,
        linuxppc-dev@...ts.ozlabs.org, x86@...nel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH RESEND 00/28] per-VMA locks proposal

On Thu, Sep 01, 2022 at 10:34:48AM -0700, Suren Baghdasaryan wrote:
> This is a proof of concept for per-vma locks idea that was discussed
> during SPF [1] discussion at LSF/MM this year [2], which concluded with
> suggestion that “a reader/writer semaphore could be put into the VMA
> itself; that would have the effect of using the VMA as a sort of range
> lock. There would still be contention at the VMA level, but it would be an
> improvement.” This patchset implements this suggested approach.

The whole reason I started the SPF thing waay back when was because one
of the primary reporters at the time had very large VMAs and a per-vma
lock wouldn't actually help anything at all.

IIRC it was either scientific code initializing a huge matrix or a
database with a giant table; I'm sure the archives have better memory
than me.