linux-kernel - Re: [PATCH gmem FIXUP] mm, compaction: make testing mapping

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Message-ID: <ZPM/vJnwI4bi9bo2@casper.infradead.org>
Date:   Sat, 2 Sep 2023 14:59:24 +0100
From:   Matthew Wilcox <willy@...radead.org>
To:     Vlastimil Babka <vbabka@...e.cz>
Cc:     seanjc@...gle.com, ackerleytng@...gle.com,
        akpm@...ux-foundation.org, anup@...infault.org,
        aou@...s.berkeley.edu, chao.p.peng@...ux.intel.com,
        chenhuacai@...nel.org, david@...hat.com, isaku.yamahata@...il.com,
        jarkko@...nel.org, jmorris@...ei.org,
        kirill.shutemov@...ux.intel.com, kvm-riscv@...ts.infradead.org,
        kvm@...r.kernel.org, kvmarm@...ts.linux.dev,
        liam.merwick@...cle.com, linux-arm-kernel@...ts.infradead.org,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-mips@...r.kernel.org, linux-mm@...ck.org,
        linux-riscv@...ts.infradead.org,
        linux-security-module@...r.kernel.org,
        linuxppc-dev@...ts.ozlabs.org, mail@...iej.szmigiero.name,
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        qperret@...gle.com, serge@...lyn.com, tabba@...gle.com,
        vannapurve@...gle.com, wei.w.wang@...el.com,
        yu.c.zhang@...ux.intel.com
Subject: Re: [PATCH gmem FIXUP] mm, compaction: make testing
 mapping_unmovable() safe

On Fri, Sep 01, 2023 at 10:20:26AM +0200, Vlastimil Babka wrote:
> As Kirill pointed out, mapping can be removed under us due to
> truncation. Test it under folio lock as already done for the async
> compaction / dirty folio case. To prevent locking every folio with
> mapping to do the test, do it only for unevictable folios, as we can
> expect the unmovable mapping folios are also unevictable - it is the
> case for guest memfd folios.
> 
> Also incorporate comment update suggested by Matthew.

In the meantime, 866ff80176aa went upstream earlier this merge window,
so it's going to have some conflicts.