[PATCH 1/4] memcg: account swap cache under lock

[KAMEZAWA Hiroyuki]

While page-cache's charge/uncharge is done under page_lock(), swap-cache
isn't. (anonymous page is charged when it's newly allocated.)

This patch moves do_swap_page()'s charge() call under lock.
I don't see any bad problem *now* but this fix will be good for future
for avoiding unneccesary racy state.


Changelog: (v5) -> (v6)
 - mark_page_accessed() is moved before lock_page().
 - fixed missing unlock_page()
(no changes in previous version)

Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>

 mm/memory.c |   11 ++++++-----
 1 file changed, 6 insertions(+), 5 deletions(-)

Index: mmotm-2.6.27-rc7+/mm/memory.c
===================================================================
--- mmotm-2.6.27-rc7+.orig/mm/memory.c
+++ mmotm-2.6.27-rc7+/mm/memory.c
@@ -2326,16 +2326,17 @@ static int do_swap_page(struct mm_struct
 		count_vm_event(PGMAJFAULT);
 	}
 
+	mark_page_accessed(page);
+
+	lock_page(page);
+	delayacct_clear_flag(DELAYACCT_PF_SWAPIN);
+
 	if (mem_cgroup_charge(page, mm, GFP_KERNEL)) {
-		delayacct_clear_flag(DELAYACCT_PF_SWAPIN);
 		ret = VM_FAULT_OOM;
+		unlock_page(page);
 		goto out;
 	}
 
-	mark_page_accessed(page);
-	lock_page(page);
-	delayacct_clear_flag(DELAYACCT_PF_SWAPIN);
-
 	/*
 	 * Back out if somebody else already faulted in this pte.
 	 */

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