linux-kernel - Re: [PATCH 27/28] mm, page_alloc: Defer debugging checks of freed pages until a PCP drain

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Message-ID: <5720A987.7060507@suse.cz>
Date:	Wed, 27 Apr 2016 13:59:03 +0200
From:	Vlastimil Babka <vbabka@...e.cz>
To:	Mel Gorman <mgorman@...hsingularity.net>,
	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Jesper Dangaard Brouer <brouer@...hat.com>,
	Linux-MM <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 27/28] mm, page_alloc: Defer debugging checks of freed
 pages until a PCP drain

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@...hsingularity.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.