From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail137.messagelabs.com (mail137.messagelabs.com [216.82.249.19]) by kanga.kvack.org (Postfix) with ESMTP id 7D9916B0047 for ; Fri, 19 Feb 2010 00:49:09 -0500 (EST) Message-ID: <4B7E2635.8010700@codeaurora.org> Date: Thu, 18 Feb 2010 21:48:37 -0800 From: Michael Bohan MIME-Version: 1.0 Subject: Re: Kernel panic due to page migration accessing memory holes References: <4B7C8DC2.3060004@codeaurora.org> <20100218100324.5e9e8f8c.kamezawa.hiroyu@jp.fujitsu.com> <4B7CF8C0.4050105@codeaurora.org> <20100218183604.95ee8c77.kamezawa.hiroyu@jp.fujitsu.com> <20100218100432.GA32626@csn.ul.ie> <4B7DEDB0.8030802@codeaurora.org> <20100219110003.dfe58df8.kamezawa.hiroyu@jp.fujitsu.com> In-Reply-To: <20100219110003.dfe58df8.kamezawa.hiroyu@jp.fujitsu.com> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org To: KAMEZAWA Hiroyuki Cc: Mel Gorman , linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-arm-msm@vger.kernel.org, linux-arm-kernel@lists.infradead.org List-ID: On 2/18/2010 6:00 PM, KAMEZAWA Hiroyuki wrote: > memmap for memory holes should be marked as PG_reserved and never be freed > by free_bootmem(). Then, memmap for memory holes will not be in buddy allocator. > > Again, pfn_valid() just show "there is memmap", not for "there is a valid page" > ARM seems to have been freeing the memmap holes for a long time. I'm pretty sure there would be a lot of pushback if we tried to change that. For example, in my memory map running FLATMEM, I would be consuming an extra ~7 MB of memory if these structures were not freed. As a compromise, perhaps we could free everything except the first 'pageblock_nr_pages' in a hole? This would guarantee that move_freepages() doesn't deference any memory that doesn't belong to the memmap -- but still only waste a relatively small amount of memory. For a 4 MB page block, it should only consume an extra 32 KB per hole in the memory map. Thanks, Michael -- 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