mm: reuse_swap_page replaces can_share_swap_page

A good place to free up old swap is where do_wp_page(), or do_swap_page(),
is about to redirty the page: the data on disk is then stale and won't be
read again; and if we do decide to write the page out later, using the
previous swap location makes an unnecessary disk seek very likely.

So give can_share_swap_page() the side-effect of delete_from_swap_cache()
when it safely can.  And can_share_swap_page() was always a misleading
name, the more so if it has a side-effect: rename it reuse_swap_page().

Irrelevant cleanup nearby: remove swap_token_default_timeout definition
from swap.h: it's used nowhere.

Signed-off-by: Hugh Dickins <hugh@veritas.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Acked-by: Rik van Riel <riel@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Robin Holt <holt@sgi.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 2 insertions, 4 deletions

diff --git a/include/linux/swap.h b/include/linux/swap.h
index 48f309dc5a0c..366556c5b148 100644
--- a/include/linux/swap.h
+++ b/include/linux/swap.h
@@ -304,7 +304,7 @@ extern unsigned int count_swap_pages(int, int);
 extern sector_t map_swap_page(struct swap_info_struct *, pgoff_t);
 extern sector_t swapdev_block(int, pgoff_t);
 extern struct swap_info_struct *get_swap_info_struct(unsigned);
-extern int can_share_swap_page(struct page *);
+extern int reuse_swap_page(struct page *);
 extern int remove_exclusive_swap_page(struct page *);
 extern int remove_exclusive_swap_page_ref(struct page *);
 struct backing_dev_info;
@@ -372,8 +372,6 @@ static inline struct page *lookup_swap_cache(swp_entry_t swp)
         return NULL;
 }
 
-#define can_share_swap_page(p)                  (page_mapcount(p) == 1)
-
 static inline int add_to_swap_cache(struct page *page, swp_entry_t entry,
                                                         gfp_t gfp_mask)
 {
@@ -388,7 +386,7 @@ static inline void delete_from_swap_cache(struct page *page)
 {
 }
 
-#define swap_token_default_timeout              0
+#define reuse_swap_page(page)   (page_mapcount(page) == 1)
 
 static inline int remove_exclusive_swap_page(struct page *p)
 {