FS-Cache: Recruit a page flags for cache management

Recruit a page flag to aid in cache management.  The following extra flag is
defined:

 (1) PG_fscache (PG_private_2)

     The marked page is backed by a local cache and is pinning resources in the
     cache driver.

If PG_fscache is set, then things that checked for PG_private will now also
check for that.  This includes things like truncation and page invalidation.
The function page_has_private() had been added to make the checks for both
PG_private and PG_private_2 at the same time.

Signed-off-by: David Howells <dhowells@redhat.com>
Acked-by: Steve Dickson <steved@redhat.com>
Acked-by: Trond Myklebust <Trond.Myklebust@netapp.com>
Acked-by: Rik van Riel <riel@redhat.com>
Acked-by: Al Viro <viro@zeniv.linux.org.uk>
Tested-by: Daire Byrne <Daire.Byrne@framestore.com>

1 files changed, 5 insertions, 4 deletions

diff --git a/mm/readahead.c b/mm/readahead.c
index 6be927569cf..133b6d52551 100644
--- a/mm/readahead.c
+++ b/mm/readahead.c
@@ -33,14 +33,15 @@ EXPORT_SYMBOL_GPL(file_ra_state_init);
 
 /*
  * see if a page needs releasing upon read_cache_pages() failure
- * - the caller of read_cache_pages() may have set PG_private before calling,
- *   such as the NFS fs marking pages that are cached locally on disk, thus we
- *   need to give the fs a chance to clean up in the event of an error
+ * - the caller of read_cache_pages() may have set PG_private or PG_fscache
+ *   before calling, such as the NFS fs marking pages that are cached locally
+ *   on disk, thus we need to give the fs a chance to clean up in the event of
+ *   an error
  */
 static void read_cache_pages_invalidate_page(struct address_space *mapping,
                                              struct page *page)
 {
-        if (PagePrivate(page)) {
+        if (page_has_private(page)) {
                 if (!trylock_page(page))
                         BUG();
                 page->mapping = mapping;