From 62ade86ab6c7e26409229ca45503cae97bf698cf Mon Sep 17 00:00:00 2001 From: Hugh Dickins Date: Fri, 18 May 2012 11:28:34 -0700 Subject: [PATCH] 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 Signed-off-by: Linus Torvalds --- mm/memcontrol.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/mm/memcontrol.c b/mm/memcontrol.c index b659260..7685d4a 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; } -- 1.7.10.4