mm/filemap.c: remove redundant cache invalidation after async direct-…

…io write

generic_file_direct_write() invalidates cache at entry.  Second time this
should be done when request completes.  But this function calls second
invalidation at exit unconditionally even for async requests.

This patch skips second invalidation for async requests (-EIOCBQUEUED).

Link: http://lkml.kernel.org/r/157270037850.4812.15036239021726025572.stgit@buzz
Signed-off-by: Konstantin Khlebnikov <[email protected]>
Reviewed-by: Andrew Morton <[email protected]>
Reviewed-by: Jan Kara <[email protected]>
Cc: Jens Axboe <[email protected]>
Cc: Alexander Viro <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

mm/filemap.c

@@ -3218,9 +3218,11 @@ generic_file_direct_write(struct kiocb *iocb, struct iov_iter *from)
 	 * Most of the time we do not need this since dio_complete() will do
 	 * the invalidation for us. However there are some file systems that
 	 * do not end up with dio_complete() being called, so let's not break
-	 * them by removing it completely
+	 * them by removing it completely.
+	 *
+	 * Skip invalidation for async writes or if mapping has no pages.
 	 */
-	if (mapping->nrpages)
+	if (written > 0 && mapping->nrpages)
 		invalidate_inode_pages2_range(mapping,
 					pos >> PAGE_SHIFT, end);