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

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Message-ID: <20230901210555.j5d5a4azmkxzlnn2@box.shutemov.name>
Date:   Sat, 2 Sep 2023 00:05:55 +0300
From:   kirill.shutemov@...ux.intel.com
To:     Vlastimil Babka <vbabka@...e.cz>
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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.
> 
> Fixes: 3424873596ce ("mm: Add AS_UNMOVABLE to mark mapping as completely unmovable")
> Signed-off-by: Vlastimil Babka <vbabka@...e.cz>

Superficially looks good to me. But I don't really understand this
code path to Ack.

-- 
  Kiryl Shutsemau / Kirill A. Shutemov