swap_info: note SWAP_MAP_SHMEM

While we're fiddling with the swap_map values, let's assign a particular
value to shmem/tmpfs swap pages: their swap counts are never incremented,
and it helps swapoff's try_to_unuse() a little if it can immediately
distinguish those pages from process pages.

Since we've no use for SWAP_MAP_BAD | COUNT_CONTINUED,
we might as well use that 0xbf value for SWAP_MAP_SHMEM.

Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Reviewed-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Rik van Riel <riel@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 9 insertions, 2 deletions

diff --git a/mm/shmem.c b/mm/shmem.c
index 356dd99566ec..4fb41c83daca 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -1017,7 +1017,14 @@ int shmem_unuse(swp_entry_t entry, struct page *page)
                         goto out;
         }
         mutex_unlock(&shmem_swaplist_mutex);
-out:    return found;   /* 0 or 1 or -ENOMEM */
+        /*
+         * Can some race bring us here?  We've been holding page lock,
+         * so I think not; but would rather try again later than BUG()
+         */
+        unlock_page(page);
+        page_cache_release(page);
+out:
+        return (found < 0) ? found : 0;
 }
 
 /*
@@ -1080,7 +1087,7 @@ static int shmem_writepage(struct page *page, struct writeback_control *wbc)
                 else
                         inode = NULL;
                 spin_unlock(&info->lock);
-                swap_duplicate(swap);
+                swap_shmem_alloc(swap);
                 BUG_ON(page_mapped(page));
                 page_cache_release(page);       /* pagecache ref */
                 swap_writepage(page, wbc);