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mm: modify swap_map and add SWAP_HAS_CACHE flag

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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>
This commit is contained in:
KAMEZAWA Hiroyuki
2009-06-16 15:32:53 -07:00
committed by Linus Torvalds
parent cb4b86ba47
commit 355cfa73dd
3 changed files with 171 additions and 60 deletions
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14
include/linux/swap.h
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@ -129,9 +129,10 @@ enum {
#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 long total_swap_pages;
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 @@ static inline void show_swap_cache_info(void)
}
#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)
{
}