Re: [PATCH] mm/khugepaged: don't map folios that are not uptodate in MADV_COLLAPSE

[SJ Park]

On Thu, 05 Nov 2026 19:16:44 +0100 "David Hildenbrand (Arm)" <david@xxxxxxxxxx> wrote:

> madvise(MADV_COLLAPSE) can map PMD-sized pagecache folios that are not
> uptodate. For example, shmem fallocate() can put such folios into the
> page cache.
> 
> collapse_file() already refuses to proceed with folios that are not
> uptodate. Let's just do the same in try_collapse_pte_mapped_thp() and skip
> such folios, leaving handling to the page faults.
> 
> Note that collapse_file() effectively clears shmem folios through
> shmem_get_folio(); let's keep this fix simple and simply let the page
> fault path deal with that.

Makes sense to me.

> 
> Fixes: 34488399fa08 ("mm/madvise: add file and shmem support to MADV_COLLAPSE")
> Reported-by: Chris Mason <mason@xxxxxxxxxx>
> Cc: stable@xxxxxxxxxxxxxxx
> Signed-off-by: David Hildenbrand (Arm) <david@xxxxxxxxxx>

Reviewed-by: SJ Park <sj@xxxxxxxxxx>


Thanks,
SJ

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