From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail172.messagelabs.com (mail172.messagelabs.com [216.82.254.3]) by kanga.kvack.org (Postfix) with SMTP id 1FA116B004A for ; Wed, 13 Jul 2011 19:34:59 -0400 (EDT) Date: Thu, 14 Jul 2011 09:34:49 +1000 From: Dave Chinner Subject: Re: [PATCH 1/5] mm: vmscan: Do not writeback filesystem pages in direct reclaim Message-ID: <20110713233449.GU23038@dastard> References: <1310567487-15367-1-git-send-email-mgorman@suse.de> <1310567487-15367-2-git-send-email-mgorman@suse.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1310567487-15367-2-git-send-email-mgorman@suse.de> Sender: owner-linux-mm@kvack.org List-ID: To: Mel Gorman Cc: Linux-MM , LKML , XFS , Christoph Hellwig , Johannes Weiner , Wu Fengguang , Jan Kara , Rik van Riel , Minchan Kim On Wed, Jul 13, 2011 at 03:31:23PM +0100, Mel Gorman wrote: > From: Mel Gorman > > When kswapd is failing to keep zones above the min watermark, a process > will enter direct reclaim in the same manner kswapd does. If a dirty > page is encountered during the scan, this page is written to backing > storage using mapping->writepage. > > This causes two problems. First, it can result in very deep call > stacks, particularly if the target storage or filesystem are complex. > Some filesystems ignore write requests from direct reclaim as a result. > The second is that a single-page flush is inefficient in terms of IO. > While there is an expectation that the elevator will merge requests, > this does not always happen. Quoting Christoph Hellwig; > > The elevator has a relatively small window it can operate on, > and can never fix up a bad large scale writeback pattern. > > This patch prevents direct reclaim writing back filesystem pages by > checking if current is kswapd. Anonymous pages are still written to > swap as there is not the equivalent of a flusher thread for anonymos > pages. If the dirty pages cannot be written back, they are placed > back on the LRU lists. > > Signed-off-by: Mel Gorman Ok, so that makes the .writepage checks in ext4, xfs and btrfs for this condition redundant. In effect the patch should be a no-op for those filesystems. Can you also remove the checks in the filesystems? Cheers, Dave. -- Dave Chinner david@fromorbit.com -- 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