From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail190.messagelabs.com (mail190.messagelabs.com [216.82.249.51]) by kanga.kvack.org (Postfix) with ESMTP id E773B6B004A for ; Thu, 9 Sep 2010 05:22:19 -0400 (EDT) Date: Thu, 9 Sep 2010 10:22:03 +0100 From: Mel Gorman Subject: Re: [PATCH 05/10] vmscan: Synchrounous lumpy reclaim use lock_page() instead trylock_page() Message-ID: <20100909092203.GL29263@csn.ul.ie> References: <20100909120448.58acc9a6.kamezawa.hiroyu@jp.fujitsu.com> <20100909121547.2e69735a.kamezawa.hiroyu@jp.fujitsu.com> <20100909131211.C93C.A69D9226@jp.fujitsu.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-15 Content-Disposition: inline In-Reply-To: <20100909131211.C93C.A69D9226@jp.fujitsu.com> Sender: owner-linux-mm@kvack.org To: KOSAKI Motohiro Cc: KAMEZAWA Hiroyuki , linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, Linux Kernel List , Rik van Riel , Johannes Weiner , Minchan Kim , Wu Fengguang , Andrea Arcangeli , Dave Chinner , Chris Mason , Christoph Hellwig , Andrew Morton List-ID: On Thu, Sep 09, 2010 at 01:13:22PM +0900, KOSAKI Motohiro wrote: > > On Thu, 9 Sep 2010 12:04:48 +0900 > > KAMEZAWA Hiroyuki wrote: > > > > > On Mon, 6 Sep 2010 11:47:28 +0100 > > > Mel Gorman wrote: > > > > > > > From: KOSAKI Motohiro > > > > > > > > With synchrounous lumpy reclaim, there is no reason to give up to reclaim > > > > pages even if page is locked. This patch uses lock_page() instead of > > > > trylock_page() in this case. > > > > > > > > Signed-off-by: KOSAKI Motohiro > > > > Signed-off-by: Mel Gorman > > > > > > Reviewed-by: KAMEZAWA Hiroyuki > > > > > Ah......but can't this change cause dead lock ?? > > Yes, this patch is purely crappy. please drop. I guess I was poisoned > by poisonous mushroom of Mario Bros. > Lets be clear on what the exact dead lock conditions are. The ones I had thought about when I felt this patch was ok were; o We are not holding the LRU lock (or any lock, we just called cond_resched()) o We do not have another page locked because we cannot lock multiple pages o Kswapd will never be in LUMPY_MODE_SYNC so it is not getting blocked o lock_page() itself is not allocating anything that we could recurse on One potential dead lock would be if the direct reclaimer held a page lock and ended up here but is that situation even allowed? I did not think of an obvious example of when this would happen. Similarly, deadlock situations with mmap_sem shouldn't happen unless multiple page locks are being taken. (prepares to feel foolish) What did I miss? -- Mel Gorman Part-time Phd Student Linux Technology Center University of Limerick IBM Dublin Software Lab -- 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