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authorHugh Dickins <hughd@google.com>2012-05-18 11:28:34 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2012-05-19 10:10:27 -0700
commit62ade86ab6c7e26409229ca45503cae97bf698cf (patch)
tree569ce54e1fce1f985cc9525712c39b2b020e1fdf
parentb1dab2f0409c478fd2d9e227c2c018524eca9603 (diff)
downloadlinux-stericsson-62ade86ab6c7e26409229ca45503cae97bf698cf.tar.gz
memcg,thp: fix res_counter:96 regression
Occasionally, testing memcg's move_charge_at_immigrate on rc7 shows a flurry of hundreds of warnings at kernel/res_counter.c:96, where res_counter_uncharge_locked() does WARN_ON(counter->usage < val). The first trace of each flurry implicates __mem_cgroup_cancel_charge() of mc.precharge, and an audit of mc.precharge handling points to mem_cgroup_move_charge_pte_range()'s THP handling in commit 12724850e806 ("memcg: avoid THP split in task migration"). Checking !mc.precharge is good everywhere else, when a single page is to be charged; but here the "mc.precharge -= HPAGE_PMD_NR" likely to follow, is liable to result in underflow (a lot can change since the precharge was estimated). Simply check against HPAGE_PMD_NR: there's probably a better alternative, trying precharge for more, splitting if unsuccessful; but this one-liner is safer for now - no kernel/res_counter.c:96 warnings seen in 26 hours. Signed-off-by: Hugh Dickins <hughd@google.com> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
-rw-r--r--mm/memcontrol.c2
1 files changed, 1 insertions, 1 deletions
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index b659260c56ad..7685d4a0b3ce 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -5481,7 +5481,7 @@ static int mem_cgroup_move_charge_pte_range(pmd_t *pmd,
* part of thp split is not executed yet.
*/
if (pmd_trans_huge_lock(pmd, vma) == 1) {
- if (!mc.precharge) {
+ if (mc.precharge < HPAGE_PMD_NR) {
spin_unlock(&vma->vm_mm->page_table_lock);
return 0;
}