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 S1754613AbdBHOEY (ORCPT <rfc822;w@1wt.eu>);
        Wed, 8 Feb 2017 09:04:24 -0500
Received: from Galois.linutronix.de ([146.0.238.70]:53929 "EHLO
        Galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
        with ESMTP id S1754292AbdBHOEQ (ORCPT
        <rfc822;linux-kernel@vger.kernel.org>);
        Wed, 8 Feb 2017 09:04:16 -0500
Date: Wed, 8 Feb 2017 14:23:19 +0100 (CET)
From: Thomas Gleixner <tglx@linutronix.de>
To: Mel Gorman <mgorman@techsingularity.net>
cc: Michal Hocko <mhocko@kernel.org>, Christoph Lameter <cl@linux.com>,
        Vlastimil Babka <vbabka@suse.cz>, Dmitry Vyukov <dvyukov@google.com>,
        Tejun Heo <tj@kernel.org>, "linux-mm@kvack.org" <linux-mm@kvack.org>,
        LKML <linux-kernel@vger.kernel.org>, Ingo Molnar <mingo@kernel.org>,
        Peter Zijlstra <peterz@infradead.org>,
        syzkaller <syzkaller@googlegroups.com>,
        Andrew Morton <akpm@linux-foundation.org>
Subject: Re: mm: deadlock between get_online_cpus/pcpu_alloc
In-Reply-To: <20170208122612.wasq72hbj4nkh7y3@techsingularity.net>
Message-ID: <alpine.DEB.2.20.1702081419500.3536@nanos>
References: <20170207123708.GO5065@dhcp22.suse.cz> <20170207135846.usfrn7e4znjhmogn@techsingularity.net> <20170207141911.GR5065@dhcp22.suse.cz> <20170207153459.GV5065@dhcp22.suse.cz> <20170207162224.elnrlgibjegswsgn@techsingularity.net> <20170207164130.GY5065@dhcp22.suse.cz>
 <alpine.DEB.2.20.1702071053380.16150@east.gentwo.org> <alpine.DEB.2.20.1702072319200.8117@nanos> <20170208073527.GA5686@dhcp22.suse.cz> <alpine.DEB.2.20.1702081253590.3536@nanos> <20170208122612.wasq72hbj4nkh7y3@techsingularity.net>
User-Agent: Alpine 2.20 (DEB 67 2015-01-07)
MIME-Version: 1.0
Content-Type: text/plain; charset=US-ASCII
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

On Wed, 8 Feb 2017, Mel Gorman wrote:
> It may be worth noting that patches in Andrew's tree no longer disable
> interrupts in the per-cpu allocator and now per-cpu draining will
> be from workqueue context. The reasoning was due to the overhead of
> the page allocator with figures included. Interrupts will bypass the
> per-cpu allocator and use the irq-safe zone->lock to allocate from
> the core.  It'll collide with the RT patch. Primary patch of interest is
> http://www.ozlabs.org/~akpm/mmots/broken-out/mm-page_alloc-only-use-per-cpu-allocator-for-irq-safe-requests.patch

Yeah, we'll sort that out once it hits Linus tree and we move RT forward.
Though I have once complaint right away:

+	preempt_enable_no_resched();

This is a nono, even in mainline. You effectively disable a preemption
point.

> The draining from workqueue context may be a problem for RT but one
> option would be to move the drain to only drain for high-order pages
> after direct reclaim combined with only draining for order-0 if
> __alloc_pages_may_oom is about to be called.

Why would the draining from workqueue context be an issue on RT?

Thanks,

	tglx