From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx204.postini.com [74.125.245.204]) by kanga.kvack.org (Postfix) with SMTP id C30F56B0082 for ; Fri, 18 May 2012 14:29:00 -0400 (EDT) Received: by pbbrp2 with SMTP id rp2so6377978pbb.14 for ; Fri, 18 May 2012 11:28:59 -0700 (PDT) Date: Fri, 18 May 2012 11:28:34 -0700 (PDT) From: Hugh Dickins Subject: [PATCH] memcg,thp: fix res_counter:96 regression Message-ID: MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: owner-linux-mm@kvack.org List-ID: To: Linus Torvalds Cc: Andrew Morton , Naoya Horiguchi , KAMEZAWA Hiroyuki , Andrea Arcangeli , David Rientjes , linux-mm@kvack.org, linux-kernel@vger.kernel.org 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 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 --- mm/memcontrol.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) --- 3.4-rc7/mm/memcontrol.c 2012-05-12 22:56:05.340002552 -0700 +++ linux/mm/memcontrol.c 2012-05-17 09:39:45.944034396 -0700 @@ -5481,7 +5481,7 @@ static int mem_cgroup_move_charge_pte_ra * 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; } -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: email@kvack.org