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shmem: document how to "persist" data when using shmem_*file_setup

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Add a blurb that simply dirtying the folio will persist data for in-kernel
shmem files.  This is what most of the callers already do.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: "Matthew Wilcox (Oracle)" <willy@infradead.org>
Reviewed-by: "Darrick J. Wong" <djwong@kernel.org>
Signed-off-by: Chandan Babu R <chandanbabu@kernel.org>
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Christoph Hellwig 2024-02-19 07:27:15 +01:00 committed by Chandan Babu R
parent be9d93661d
commit 9d8b367449
1 changed files with 4 additions and 0 deletions
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mm/shmem.c
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@ -2147,6 +2147,10 @@ unlock:
* Looks up the page cache entry at @inode & @index. If a folio is
* present, it is returned locked with an increased refcount.
*
* If the caller modifies data in the folio, it must call folio_mark_dirty()
* before unlocking the folio to ensure that the folio is not reclaimed.
* There is no need to reserve space before calling folio_mark_dirty().
*
* When no folio is found, the behavior depends on @sgp:
* - for SGP_READ, *foliop is %NULL and 0 is returned
* - for SGP_NOALLOC, *foliop is %NULL and -ENOENT is returned