linux-kernel - Re: Deadlock possibly caused by too_many

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Date:	Tue, 19 Oct 2010 12:09:29 +0900
From:	Minchan Kim <minchan.kim@...il.com>
To:	Wu Fengguang <fengguang.wu@...el.com>
Cc:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Neil Brown <neilb@...e.de>, Rik van Riel <riel@...hat.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"Li, Shaohua" <shaohua.li@...el.com>
Subject: Re: Deadlock possibly caused by too_many_isolated.

On Tue, Oct 19, 2010 at 12:05 PM, Wu Fengguang <fengguang.wu@...el.com> wrote:
> On Tue, Oct 19, 2010 at 10:52:47AM +0800, Minchan Kim wrote:
>> Hi Wu,
>>
>> On Tue, Oct 19, 2010 at 11:35 AM, Wu Fengguang <fengguang.wu@...el.com> wrote:
>> >> @@ -2054,10 +2069,11 @@ rebalance:
>> >>                 goto got_pg;
>> >>
>> >>         /*
>> >> -        * If we failed to make any progress reclaiming, then we are
>> >> -        * running out of options and have to consider going OOM
>> >> +        * If we failed to make any progress reclaiming and there aren't
>> >> +        * many parallel reclaiming, then we are unning out of options and
>> >> +        * have to consider going OOM
>> >>          */
>> >> -       if (!did_some_progress) {
>> >> +       if (!did_some_progress && !too_many_isolated_zone(preferred_zone)) {
>> >>                 if ((gfp_mask & __GFP_FS) && !(gfp_mask & __GFP_NORETRY)) {
>> >>                         if (oom_killer_disabled)
>> >>                                 goto nopage;
>> >
>> > This is simply wrong.
>> >
>> > It disabled this block for 99% system because there won't be enough
>> > tasks to make (!too_many_isolated_zone == true). As a result the LRU
>> > will be scanned like mad and no task get OOMed when it should be.
>>
>> If !too_many_isolated_zone is false, it means there are already many
>> direct reclaiming tasks.
>> So they could exit reclaim path and !too_many_isolated_zone will be true.
>> What am I missing now?
>
> Ah sorry, my brain get short circuited.. but I still feel uneasy with
> this change. It's not fixing the root cause and won't prevent too many
> LRU pages be isolated. It's too late to test too_many_isolated_zone()
> after direct reclaim returns (after sleeping for a long time).
>

Intend to agree.
I think root cause is a infinite looping in too_many_isolated holding FS lock.
Would it be simple that too_many_isolated would be bail out after some try?


> Thanks,
> Fengguang
>



-- 
Kind regards,
Minchan Kim
--
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