From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx110.postini.com [74.125.245.110]) by kanga.kvack.org (Postfix) with SMTP id 46EC16B006C for ; Thu, 20 Dec 2012 17:45:25 -0500 (EST) Message-ID: <50D3951E.50107@redhat.com> Date: Thu, 20 Dec 2012 17:45:50 -0500 From: Rik van Riel MIME-Version: 1.0 Subject: Re: [PATCH] mm: compaction: Do not accidentally skip pageblocks in the migrate scanner References: <20121220142232.GA13367@suse.de> In-Reply-To: <20121220142232.GA13367@suse.de> Content-Type: text/plain; charset=ISO-8859-15; format=flowed Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Mel Gorman Cc: Andrew Morton , linux-mm@kvack.org, linux-kernel@vger.kernel.org On 12/20/2012 09:22 AM, Mel Gorman wrote: > Compaction uses the ALIGN macro incorrectly with the migrate scanner by > adding pageblock_nr_pages to a PFN. It happened to work when initially > implemented as the starting PFN was also aligned but with caching restarts > and isolating in smaller chunks this is no longer always true. The impact is > that the migrate scanner scans outside its current pageblock. As pfn_valid() > is still checked properly it does not cause any failure and the impact > of the bug is that in some cases it will scan more than necessary when > it crosses a page boundary but by no more than COMPACT_CLUSTER_MAX. It > is highly unlikely this is even measurable but it's still wrong so this > patch addresses the problem. > > Signed-off-by: Mel Gorman Reviewed-by: Rik van Riel -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org