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Date: Mon, 27 Feb 2017 18:14:04 +0100
From: Michal Hocko <mhocko@kernel.org>
Subject: Re: [PATCH v2 3/3] percpu: improve allocation success rate for
 non-GFP_KERNEL callers
Message-ID: <20170227171404.GP26504@dhcp22.suse.cz>
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To: Tahsin Erdogan <tahsin@google.com>
Cc: Tejun Heo <tj@kernel.org>, Christoph Lameter <cl@linux.com>, Andrew Morton <akpm@linux-foundation.org>, Chris Wilson <chris@chris-wilson.co.uk>, Andrey Ryabinin <aryabinin@virtuozzo.com>, Roman Pen <r.peniaev@gmail.com>, Joonas Lahtinen <joonas.lahtinen@linux.intel.com>, zijun_hu <zijun_hu@htc.com>, Joonsoo Kim <iamjoonsoo.kim@lge.com>, David Rientjes <rientjes@google.com>, linux-mm@kvack.org, linux-kernel@vger.kernel.org

On Mon 27-02-17 18:07:53, Michal Hocko wrote:
> On Mon 27-02-17 09:01:09, Tahsin Erdogan wrote:
> > On Mon, Feb 27, 2017 at 7:25 AM, Michal Hocko <mhocko@kernel.org> wrote:
> > >         /*
> > >          * No space left.  Create a new chunk.  We don't want multiple
> > >          * tasks to create chunks simultaneously.  Serialize and create iff
> > >          * there's still no empty chunk after grabbing the mutex.
> > >          */
> > >         if (is_atomic)
> > >                 goto fail;
> > >
> > > right before pcpu_populate_chunk so is this actually a problem?
> > 
> > Yes, this prevents adding more pcpu chunks and so cause "atomic" allocations
> > to fail more easily.
> 
> Then I fail to see what is the problem you are trying to fix.

To be more specific. Could you describe what more can we do in the
vmalloc layer for GFP_NOWAIT allocations? They certainly cannot sleep
and cannot perform the reclaim so you have to rely on the background
work.
-- 
Michal Hocko
SUSE Labs

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