linux-kernel - Re: Deadlock possibly caused by too_many

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Message-ID: <20101019032145.GA3108@sli10-conroe.sh.intel.com>
Date:	Tue, 19 Oct 2010 11:21:45 +0800
From:	Shaohua Li <shaohua.li@...el.com>
To:	Minchan Kim <minchan.kim@...il.com>
Cc:	"Wu, Fengguang" <fengguang.wu@...el.com>,
	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>
Subject: Re: Deadlock possibly caused by too_many_isolated.

On Tue, Oct 19, 2010 at 11:09:29AM +0800, Minchan Kim wrote:
> 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?
I'm wondering if we need too_many_isolated_zone logic. The do_try_to_free_pages
will return progress till all zones are unreclaimable. Assume before this we
don't oomkiller. If the direct reclaim fails but has progress, it will sleep.

Thanks,
Shaohua
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