From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx167.postini.com [74.125.245.167]) by kanga.kvack.org (Postfix) with SMTP id 0DB806B002C for ; Tue, 31 Jan 2012 15:40:27 -0500 (EST) Date: Tue, 31 Jan 2012 12:40:26 -0800 From: Andrew Morton Subject: Re: [PATCH] mm: compaction: Check pfn_valid when entering a new MAX_ORDER_NR_PAGES block during isolation for migration Message-Id: <20120131124026.15c0f495.akpm@linux-foundation.org> In-Reply-To: <20120131163528.GR4065@suse.de> References: <20120131163528.GR4065@suse.de> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Mel Gorman Cc: Herbert van den Bergh , Michal Nazarewicz , Linux-MM , LKML On Tue, 31 Jan 2012 16:35:28 +0000 Mel Gorman wrote: > When isolating for migration, migration starts at the start of a zone > which is not necessarily pageblock aligned. Further, it stops isolating > when COMPACT_CLUSTER_MAX pages are isolated so migrate_pfn is generally > not aligned. > > The problem is that pfn_valid is only called on the first PFN being > checked. Lets say we have a case like this > > H = MAX_ORDER_NR_PAGES boundary > | = pageblock boundary > m = cc->migrate_pfn > f = cc->free_pfn > o = memory hole > > H------|------H------|----m-Hoooooo|ooooooH-f----|------H > > The migrate_pfn is just below a memory hole and the free scanner is > beyond the hole. When isolate_migratepages started, it scans from > migrate_pfn to migrate_pfn+pageblock_nr_pages which is now in a memory > hole. It checks pfn_valid() on the first PFN but then scans into the > hole where there are not necessarily valid struct pages. > > This patch ensures that isolate_migratepages calls pfn_valid when > necessary. > > Reported-and-tested-by: Herbert van den Bergh > Signed-off-by: Mel Gorman > Acked-by: Michal Nazarewicz The changelog forgot to describe the user-visible effects of the bug. > Cc: stable@kernel.org So he (and others) will be confused. -- 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/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: email@kvack.org