[XFS] only lock pagecache pages

SGI Modid: xfs-linux:xfs-kern:167054a

fs/xfs/linux/xfs_buf.c

@@ -503,6 +503,7 @@ _pagebuf_lookup_pages(
 		}
 	}
 
+	pb->pb_flags |= _PBF_PAGECACHE;
 mapit:
 	pb->pb_flags |= _PBF_MEM_ALLOCATED;
 	if (all_mapped) {

fs/xfs/linux/xfs_buf.h

@@ -87,6 +87,7 @@ typedef enum page_buf_flags_e {		/* pb_flags values */
 	PBF_DONT_BLOCK = (1 << 15), /* do not block in current thread	   */
 
 	/* flags used only internally */
+	_PBF_PAGECACHE = (1 << 16),	/* backed by pagecache		   */
 	_PBF_ALL_PAGES_MAPPED = (1 << 18), /* all pages in range mapped	   */
 	_PBF_ADDR_ALLOCATED = (1 << 19), /* pb_addr space was allocated	   */
 	_PBF_MEM_ALLOCATED = (1 << 20), /* underlying pages are allocated  */