From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
        id S1751714AbdB0ReM (ORCPT <rfc822;w@1wt.eu>);
        Mon, 27 Feb 2017 12:34:12 -0500
Received: from mx2.suse.de ([195.135.220.15]:58259 "EHLO mx2.suse.de"
        rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP
        id S1751291AbdB0ReH (ORCPT <rfc822;linux-kernel@vger.kernel.org>);
        Mon, 27 Feb 2017 12:34:07 -0500
Date: Mon, 27 Feb 2017 18:14:04 +0100
From: Michal Hocko <mhocko@kernel.org>
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
Subject: Re: [PATCH v2 3/3] percpu: improve allocation success rate for
 non-GFP_KERNEL callers
Message-ID: <20170227171404.GP26504@dhcp22.suse.cz>
References: <201702260805.zhem8KFI%fengguang.wu@intel.com>
 <20170226043829.14270-1-tahsin@google.com>
 <20170227095258.GG14029@dhcp22.suse.cz>
 <CAAeU0aMaGa63Nj=JvZKKy82FftAT9dF56=gZsufDvrkqDSGUrw@mail.gmail.com>
 <20170227152516.GJ26504@dhcp22.suse.cz>
 <CAAeU0aOCGrwmYGPWgA_7Y=2O2RXG_Ux14h4FrogpKPAKvVNaXg@mail.gmail.com>
 <20170227170753.GO26504@dhcp22.suse.cz>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20170227170753.GO26504@dhcp22.suse.cz>
User-Agent: Mutt/1.5.23 (2014-03-12)
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: 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