Re: [PATCH] memcg,thp: fix res_counter:96 regression

[KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>]

(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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