The logic of uncharge is
- decrement refcnt -> lock page cgroup -> remove page cgroup.
But the logic of charging is
- lock page cgroup -> increment refcnt -> return.
Then, one charge will be added to a page_cgroup under being removed.
This makes no big trouble (like panic) but one charge is lost.
This patch add a test at charging to verify page_cgroup's refcnt is
greater than 0. If not, unlock and retry.
Changelog v2->v3
* adjusted to 2.6.23-mm1
Changelog v1->v2:
* added cpu_relax() before retry.
Signed-off-by: KAMEZAWA Hiroyuki <[email protected]>
mm/memcontrol.c | 10 ++++++++--
1 file changed, 8 insertions(+), 2 deletions(-)
Index: devel-2.6.23-mm1/mm/memcontrol.c
===================================================================
--- devel-2.6.23-mm1.orig/mm/memcontrol.c
+++ devel-2.6.23-mm1/mm/memcontrol.c
@@ -281,14 +281,20 @@ int mem_cgroup_charge(struct page *page,
* to see if the cgroup page already has a page_cgroup associated
* with it
*/
+retry:
lock_page_cgroup(page);
pc = page_get_page_cgroup(page);
/*
* The page_cgroup exists and the page has already been accounted
*/
if (pc) {
- atomic_inc(&pc->ref_cnt);
- goto done;
+ if (unlikely(!atomic_inc_not_zero(&pc->ref_cnt))) {
+ /* this page is under being uncharged ? */
+ unlock_page_cgroup(page);
+ cpu_relax();
+ goto retry;
+ } else
+ goto done;
}
unlock_page_cgroup(page);
-
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