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 S1753279AbcD0L7I (ORCPT <rfc822;w@1wt.eu>);
	Wed, 27 Apr 2016 07:59:08 -0400
Received: from mx2.suse.de ([195.135.220.15]:51127 "EHLO mx2.suse.de"
	rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP
	id S1752440AbcD0L7H (ORCPT <rfc822;linux-kernel@vger.kernel.org>);
	Wed, 27 Apr 2016 07:59:07 -0400
Subject: Re: [PATCH 27/28] mm, page_alloc: Defer debugging checks of freed
 pages until a PCP drain
To: Mel Gorman <mgorman@techsingularity.net>,
        Andrew Morton <akpm@linux-foundation.org>
References: <1460710760-32601-1-git-send-email-mgorman@techsingularity.net>
 <1460711275-1130-1-git-send-email-mgorman@techsingularity.net>
 <1460711275-1130-15-git-send-email-mgorman@techsingularity.net>
Cc: Jesper Dangaard Brouer <brouer@redhat.com>, Linux-MM <linux-mm@kvack.org>,
        LKML <linux-kernel@vger.kernel.org>
From: Vlastimil Babka <vbabka@suse.cz>
Message-ID: <5720A987.7060507@suse.cz>
Date: Wed, 27 Apr 2016 13:59:03 +0200
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101
 Thunderbird/38.7.2
MIME-Version: 1.0
In-Reply-To: <1460711275-1130-15-git-send-email-mgorman@techsingularity.net>
Content-Type: text/plain; charset=utf-8; format=flowed
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

On 04/15/2016 11:07 AM, Mel Gorman wrote:
> Every page free checks a number of page fields for validity. This
> catches premature frees and corruptions but it is also expensive.
> This patch weakens the debugging check by checking PCP pages at the
> time they are drained from the PCP list. This will trigger the bug
> but the site that freed the corrupt page will be lost. To get the
> full context, a kernel rebuild with DEBUG_VM is necessary.
>
> Signed-off-by: Mel Gorman <mgorman@techsingularity.net>

I don't like the duplicated code in free_pcp_prepare() from maintenance 
perspective, as Hugh just reminded me that similar kind of duplication 
between page_alloc.c and compaction.c can easily lead to mistakes. I've 
tried to fix that, which resulted in 3 small patches I'll post as 
replies here. Could be that the ideas will be applicable also to 28/28 
which I haven't checked yet.