memcg: fix swap accounting

This patch fixes mis-accounting of swap usage in memcg.

In the current implementation, memcg's swap account is uncharged only when
swap is completely freed.  But there are several cases where swap cannot
be freed cleanly.  For handling that, this patch changes that memcg
uncharges swap account when swap has no references other than cache.

By this, memcg's swap entry accounting can be fully synchronous with the
application's behavior.

This patch also changes memcg's hooks for swap-out.

Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
Acked-by: 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>

1 files changed, 12 insertions, 4 deletions

diff --git a/mm/swapfile.c b/mm/swapfile.c
index 28faa01..d1ade1a 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -583,8 +583,9 @@ static int swap_entry_free(struct swap_info_struct *p,
 			swap_list.next = p - swap_info;
 		nr_swap_pages++;
 		p->inuse_pages--;
-		mem_cgroup_uncharge_swap(ent);
 	}
+	if (!swap_count(count))
+		mem_cgroup_uncharge_swap(ent);
 	return count;
 }
 
@@ -609,12 +610,19 @@ void swap_free(swp_entry_t entry)
 void swapcache_free(swp_entry_t entry, struct page *page)
 {
 	struct swap_info_struct *p;
+	int ret;
 
-	if (page)
-		mem_cgroup_uncharge_swapcache(page, entry);
 	p = swap_info_get(entry);
 	if (p) {
-		swap_entry_free(p, entry, SWAP_CACHE);
+		ret = swap_entry_free(p, entry, SWAP_CACHE);
+		if (page) {
+			bool swapout;
+			if (ret)
+				swapout = true; /* the end of swap out */
+			else
+				swapout = false; /* no more swap users! */
+			mem_cgroup_uncharge_swapcache(page, entry, swapout);
+		}
 		spin_unlock(&swap_lock);
 	}
 	return;