From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail191.messagelabs.com (mail191.messagelabs.com [216.82.242.19]) by kanga.kvack.org (Postfix) with ESMTP id DA5E36B0096 for ; Fri, 3 Dec 2010 07:12:17 -0500 (EST) Date: Fri, 3 Dec 2010 12:11:53 +0000 From: Mel Gorman Subject: Re: [PATCH] vmscan: make kswapd use a correct order Message-ID: <20101203121153.GB13268@csn.ul.ie> References: <1291305649-2405-1-git-send-email-minchan.kim@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-15 Content-Disposition: inline In-Reply-To: <1291305649-2405-1-git-send-email-minchan.kim@gmail.com> Sender: owner-linux-mm@kvack.org To: Minchan Kim Cc: Andrew Morton , linux-mm , LKML , Shaohua Li , KOSAKI Motohiro List-ID: On Fri, Dec 03, 2010 at 01:00:49AM +0900, Minchan Kim wrote: > If we wake up prematurely, it means we should keep going on > reclaiming not new order page but at old order page. > Sometime new order can be smaller than old order by below > race so it could make failure of old order page reclaiming. > > T0: Task 1 wakes up kswapd with order-3 > T1: So, kswapd starts to reclaim pages using balance_pgdat > T2: Task 2 wakes up kswapd with order-2 because pages reclaimed > by T1 are consumed quickly. > T3: kswapd exits balance_pgdat and will do following: > T4-1: In beginning of kswapd's loop, pgdat->kswapd_max_order will > be reset with zero. > T4-2: 'order' will be set to pgdat->kswapd_max_order(0), since it > enters the false branch of 'if (order (3) < new_order (2))' > T4-3: If previous balance_pgdat can't meet requirement of order-2 > free pages by high watermark, it will start reclaiming again. > So balance_pgdat will use order-0 to do reclaim while it > really should use order-2 at the moment. > T4-4: At last, Task 1 can't get the any page if it wanted with > GFP_ATOMIC. > > Reported-by: Shaohua Li > Signed-off-by: Minchan Kim > Reviewed-by: KOSAKI Motohiro > Reviewed-by: Shaohua Li > Cc: Mel Gorman Acked-by: Mel Gorman -- 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/ . Fight unfair telecom policy in Canada: sign http://dissolvethecrtc.ca/ Don't email: email@kvack.org