mm: modify swap_map and add SWAP_HAS_CACHE flag
This is a part of the patches for fixing memcg's swap accountinf leak.
But, IMHO, not a bad patch even if no memcg.
There are 2 kinds of references to swap.
- reference from swap entry
- reference from swap cache
Then,
- If there is swap cache && swap's refcnt is 1, there is only swap cache.
(*) swapcount(entry) == 1 && find_get_page(swapper_space, entry) != NULL
This counting logic have worked well for a long time. But considering
that we cannot know there is a _real_ reference or not by swap_map[],
current usage of counter is not very good.
This patch adds a flag SWAP_HAS_CACHE and recored information that a swap
entry has a cache or not. This will remove -1 magic used in swapfile.c
and be a help to avoid unnecessary find_get_page().
Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Tested-by: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Li Zefan <lizf@cn.fujitsu.com>
Cc: Dhaval Giani <dhaval@linux.vnet.ibm.com>
Cc: YAMAMOTO Takashi <yamamoto@valinux.co.jp>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/include/linux/swap.h b/include/linux/swap.h
index 259e96c..fed5e8e 100644
--- a/include/linux/swap.h
+++ b/include/linux/swap.h
@@ -129,9 +129,10 @@
#define SWAP_CLUSTER_MAX 32
-#define SWAP_MAP_MAX 0x7fff
-#define SWAP_MAP_BAD 0x8000
-
+#define SWAP_MAP_MAX 0x7ffe
+#define SWAP_MAP_BAD 0x7fff
+#define SWAP_HAS_CACHE 0x8000 /* There is a swap cache of entry. */
+#define SWAP_COUNT_MASK (~SWAP_HAS_CACHE)
/*
* The in-memory structure used to track swap areas.
*/
@@ -281,7 +282,7 @@
extern void si_swapinfo(struct sysinfo *);
extern swp_entry_t get_swap_page(void);
extern swp_entry_t get_swap_page_of_type(int);
-extern int swap_duplicate(swp_entry_t);
+extern void swap_duplicate(swp_entry_t);
extern int swapcache_prepare(swp_entry_t);
extern int valid_swaphandles(swp_entry_t, unsigned long *);
extern void swap_free(swp_entry_t);
@@ -353,9 +354,12 @@
}
#define free_swap_and_cache(swp) is_migration_entry(swp)
-#define swap_duplicate(swp) is_migration_entry(swp)
#define swapcache_prepare(swp) is_migration_entry(swp)
+static inline void swap_duplicate(swp_entry_t swp)
+{
+}
+
static inline void swap_free(swp_entry_t swp)
{
}