linux-kernel - Re: 4.8.8 kernel trigger OOM killer repeatedly when I have lots of RAM that should be free

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Date:   Wed, 23 Nov 2016 08:00:02 +0100
From:   Michal Hocko <mhocko@...nel.org>
To:     Hillf Danton <hillf.zj@...baba-inc.com>
Cc:     'Linus Torvalds' <torvalds@...ux-foundation.org>,
        'Vlastimil Babka' <vbabka@...e.cz>,
        'Marc MERLIN' <marc@...lins.org>,
        'linux-mm' <linux-mm@...ck.org>,
        'LKML' <linux-kernel@...r.kernel.org>,
        'Joonsoo Kim' <iamjoonsoo.kim@....com>,
        'Tejun Heo' <tj@...nel.org>,
        'Greg Kroah-Hartman' <gregkh@...uxfoundation.org>
Subject: Re: 4.8.8 kernel trigger OOM killer repeatedly when I have lots of
 RAM that should be free

On Wed 23-11-16 14:53:12, Hillf Danton wrote:
> On Wednesday, November 23, 2016 2:34 PM Michal Hocko wrote:
> > @@ -3161,6 +3161,16 @@ should_compact_retry(struct alloc_context *ac, unsigned int order, int alloc_fla
> >  	if (!order || order > PAGE_ALLOC_COSTLY_ORDER)
> >  		return false;
> > 
> > +#ifdef CONFIG_COMPACTION
> > +	/*
> > +	 * This is a gross workaround to compensate a lack of reliable compaction
> > +	 * operation. We cannot simply go OOM with the current state of the compaction
> > +	 * code because this can lead to pre mature OOM declaration.
> > +	 */
> > +	if (order <= PAGE_ALLOC_COSTLY_ORDER)
> 
> No need to check order once more.

yes simple return true would be sufficient but I wanted the code to be
more obvious.

> Plus can we retry without CONFIG_COMPACTION enabled?

Yes checking the order-0 watermark was the original implementation of
the high order retry without compaction enabled. I do not rememeber any
reports for that so I didn't want to touch that path.
-- 
Michal Hocko
SUSE Labs