linux-kernel - Re: [PATCH v4 3/3] mm/khugepaged: maintain page cache uptodate flag

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Message-ID: <Y/VDLvLpiHkRgVjs@x1n>
Date:   Tue, 21 Feb 2023 17:18:22 -0500
From:   Peter Xu <peterx@...hat.com>
To:     David Stevens <stevensd@...omium.org>
Cc:     linux-mm@...ck.org, Matthew Wilcox <willy@...radead.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "Kirill A . Shutemov" <kirill@...temov.name>,
        Yang Shi <shy828301@...il.com>,
        David Hildenbrand <david@...hat.com>,
        Hugh Dickins <hughd@...gle.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 3/3] mm/khugepaged: maintain page cache uptodate flag

On Fri, Feb 17, 2023 at 05:54:39PM +0900, David Stevens wrote:
> From: David Stevens <stevensd@...omium.org>
> 
> Make sure that collapse_file doesn't interfere with checking the
> uptodate flag in the page cache by only inserting hpage into the page
> cache after it has been updated and marked uptodate. This is achieved by
> simply not replacing present pages with hpage when iterating over them
> target range. The present pages are already locked, so replacing the
> with the locked hpage before the collapse is finalized is unnecessary.
> 
> This fixes a race where folio_seek_hole_data would mistake hpage for
> an fallocated but unwritten page. This race is visible to userspace via
> data temporarily disappearing from SEEK_DATA/SEEK_HOLE.
> 
> Fixes: f3f0e1d2150b ("khugepaged: add support of collapse for tmpfs/shmem pages")
> Signed-off-by: David Stevens <stevensd@...omium.org>

Per my knowledge, this one looks all correct too.

Acked-by: Peter Xu <peterx@...hat.com>

So at least to me the whole set looks mostly good except patch 1 needs some
confirmation.

Thanks,

-- 
Peter Xu