Message-ID: <4FBA1841.40506@jp.fujitsu.com>
Date: Mon, 21 May 2012 19:26:09 +0900
From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
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To: Hugh Dickins <hughd@google.com>
CC: Linus Torvalds <torvalds@linux-foundation.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>,
        Andrea Arcangeli <aarcange@redhat.com>,
        David Rientjes <rientjes@google.com>, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH] memcg,thp: fix res_counter:96 regression
References: <alpine.LSU.2.00.1205181116160.2082@eggly.anvils>
In-Reply-To: <alpine.LSU.2.00.1205181116160.2082@eggly.anvils>
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(2012/05/19 3:28), Hugh Dickins wrote:

> 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 <hughd@google.com>


Thank you.

Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>


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