From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail203.messagelabs.com (mail203.messagelabs.com [216.82.254.243]) by kanga.kvack.org (Postfix) with SMTP id D44ED8D003B for ; Sat, 23 Apr 2011 23:15:35 -0400 (EDT) Date: Sun, 24 Apr 2011 11:15:31 +0800 From: Wu Fengguang Subject: Re: [PATCH 5/6] writeback: sync expired inodes first in background writeback Message-ID: <20110424031531.GA11220@localhost> References: <20110420080336.441157866@intel.com> <20110420080918.383880412@intel.com> <20110420164005.e3925965.akpm@linux-foundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20110420164005.e3925965.akpm@linux-foundation.org> Sender: owner-linux-mm@kvack.org List-ID: To: Andrew Morton Cc: Jan Kara , Mel Gorman , Dave Chinner , Rik van Riel , Mel Gorman , Itaru Kitayama , Minchan Kim , Linux Memory Management List , "linux-fsdevel@vger.kernel.org" , LKML > One of the many requirements for writeback is that if userspace is > continually dirtying pages in a particular file, that shouldn't cause > the kupdate function to concentrate on that file's newly-dirtied pages, > neglecting pages from other files which were less-recently dirtied. > (and dirty nodes, etc). Sadly I do find the old pages that the flusher never get a chance to catch and write them out. In the below case, if the task dirties pages fast enough at the end of file, writeback_index will never get a chance to wrap back. There may be various variations of this case. file head [ *** ==>***************]==> old pages writeback_index fresh dirties Ironically the current kernel relies on pageout() to catch these old pages, which is not only inefficient, but also not reliable. If a full LRU walk takes an hour, the old pages may stay dirtied for an hour. We may have to do (conditional) tagged ->writepages to safeguard users from losing data he'd expect to be written hours ago. Thanks, Fengguang -- 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