On Mon, Jul 10, 2023 at 02:02:48PM +0100, Matthew Wilcox (Oracle) wrote: > The filesystem ->release_folio method is called under more circumstances > now than when the documentation was written. The second sentence > describing the interpretation of the return value is the wrong polarity > (false indicates failure, not success). And the third sentence is also > wrong (the kernel calls try_to_free_buffers() instead). > > So replace the entire paragraph with a detailed description of what the > state of the folio may be, the meaning of the gfp parameter, why the > method is being called and what the filesystem is expected to do. > > Signed-off-by: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx> > Reviewed-by: Christoph Hellwig <hch@xxxxxx> Thank you! Reviewed-by: Darrick J. Wong <djwong@xxxxxxxxxx> --D > --- > Documentation/filesystems/locking.rst | 15 +++++++++++---- > 1 file changed, 11 insertions(+), 4 deletions(-) > > diff --git a/Documentation/filesystems/locking.rst b/Documentation/filesystems/locking.rst > index ed148919e11a..ca3d24becbf5 100644 > --- a/Documentation/filesystems/locking.rst > +++ b/Documentation/filesystems/locking.rst > @@ -374,10 +374,17 @@ invalidate_lock before invalidating page cache in truncate / hole punch > path (and thus calling into ->invalidate_folio) to block races between page > cache invalidation and page cache filling functions (fault, read, ...). > > -->release_folio() is called when the kernel is about to try to drop the > -buffers from the folio in preparation for freeing it. It returns false to > -indicate that the buffers are (or may be) freeable. If ->release_folio is > -NULL, the kernel assumes that the fs has no private interest in the buffers. > +->release_folio() is called when the MM wants to make a change to the > +folio that would invalidate the filesystem's private data. For example, > +it may be about to be removed from the address_space or split. The folio > +is locked and not under writeback. It may be dirty. The gfp parameter > +is not usually used for allocation, but rather to indicate what the > +filesystem may do to attempt to free the private data. The filesystem may > +return false to indicate that the folio's private data cannot be freed. > +If it returns true, it should have already removed the private data from > +the folio. If a filesystem does not provide a ->release_folio method, > +the pagecache will assume that private data is buffer_heads and call > +try_to_free_buffers(). > > ->free_folio() is called when the kernel has dropped the folio > from the page cache. > -- > 2.39.2 >
