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@xxxxxx> Reviewed-by: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx> Reviewed-by: Darrick J. Wong <djwong@xxxxxxxxxx> --- mm/shmem.c | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/mm/shmem.c b/mm/shmem.c index 95e70e9ea060f3..fb76da93d369cf 100644 --- a/mm/shmem.c +++ b/mm/shmem.c @@ -2147,6 +2147,10 @@ static int shmem_get_folio_gfp(struct inode *inode, pgoff_t index, * 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 -- 2.39.2
