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Date: Tue, 19 Oct 2010 11:05:16 +0800
From: Wu Fengguang <fengguang.wu@intel.com>
To: Minchan Kim <minchan.kim@gmail.com>
Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>,
        Andrew Morton <akpm@linux-foundation.org>, Neil Brown <neilb@suse.de>,
        Rik van Riel <riel@redhat.com>,
        KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "linux-mm@kvack.org" <linux-mm@kvack.org>,
        "Li, Shaohua" <shaohua.li@intel.com>
Subject: Re: Deadlock possibly caused by too_many_isolated.
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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@intel.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).

Thanks,
Fengguang