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 SMTP id 3B3816B02B9 for ; Sun, 1 Aug 2010 04:32:07 -0400 (EDT) Received: from m6.gw.fujitsu.co.jp ([10.0.50.76]) by fgwmail6.fujitsu.co.jp (Fujitsu Gateway) with ESMTP id o718W3fO026009 for (envelope-from kosaki.motohiro@jp.fujitsu.com); Sun, 1 Aug 2010 17:32:03 +0900 Received: from smail (m6 [127.0.0.1]) by outgoing.m6.gw.fujitsu.co.jp (Postfix) with ESMTP id 4BF8C45DE57 for ; Sun, 1 Aug 2010 17:32:03 +0900 (JST) Received: from s6.gw.fujitsu.co.jp (s6.gw.fujitsu.co.jp [10.0.50.96]) by m6.gw.fujitsu.co.jp (Postfix) with ESMTP id 2075B45DE51 for ; Sun, 1 Aug 2010 17:32:03 +0900 (JST) Received: from s6.gw.fujitsu.co.jp (localhost.localdomain [127.0.0.1]) by s6.gw.fujitsu.co.jp (Postfix) with ESMTP id DE499E38001 for ; Sun, 1 Aug 2010 17:32:02 +0900 (JST) Received: from m107.s.css.fujitsu.com (m107.s.css.fujitsu.com [10.249.87.107]) by s6.gw.fujitsu.co.jp (Postfix) with ESMTP id 8FE3A1DB8014 for ; Sun, 1 Aug 2010 17:32:02 +0900 (JST) From: KOSAKI Motohiro Subject: Re: [PATCH] vmscan: remove wait_on_page_writeback() from pageout() In-Reply-To: <20100801052758.GB7515@localhost> References: <20100728185457.4A82.A69D9226@jp.fujitsu.com> <20100801052758.GB7515@localhost> Message-Id: <20100801172600.4AFF.A69D9226@jp.fujitsu.com> MIME-Version: 1.0 Content-Type: text/plain; charset="US-ASCII" Content-Transfer-Encoding: 7bit Date: Sun, 1 Aug 2010 17:32:01 +0900 (JST) Sender: owner-linux-mm@kvack.org To: Wu Fengguang Cc: kosaki.motohiro@jp.fujitsu.com, Mel Gorman , Andrew Morton , Minchan Kim , Andy Whitcroft , Rik van Riel , Christoph Hellwig , "linux-kernel@vger.kernel.org" , "linux-fsdevel@vger.kernel.org" , "linux-mm@kvack.org" , Dave Chinner , Chris Mason , Nick Piggin , Johannes Weiner , KAMEZAWA Hiroyuki , Andrea Arcangeli , Andreas Mohr , Bill Davidsen , Ben Gamari List-ID: > On Wed, Jul 28, 2010 at 05:59:55PM +0800, KOSAKI Motohiro wrote: > > > On Wed, Jul 28, 2010 at 06:43:41PM +0900, KOSAKI Motohiro wrote: > > > > > On Wed, Jul 28, 2010 at 04:46:54PM +0800, Wu Fengguang wrote: > > > > > > The wait_on_page_writeback() call inside pageout() is virtually dead code. > > > > > > > > > > > > shrink_inactive_list() > > > > > > shrink_page_list(PAGEOUT_IO_ASYNC) > > > > > > pageout(PAGEOUT_IO_ASYNC) > > > > > > shrink_page_list(PAGEOUT_IO_SYNC) > > > > > > pageout(PAGEOUT_IO_SYNC) > > > > > > > > > > > > Because shrink_page_list/pageout(PAGEOUT_IO_SYNC) is always called after > > > > > > a preceding shrink_page_list/pageout(PAGEOUT_IO_ASYNC), the first > > > > > > pageout(ASYNC) converts dirty pages into writeback pages, the second > > > > > > shrink_page_list(SYNC) waits on the clean of writeback pages before > > > > > > calling pageout(SYNC). The second shrink_page_list(SYNC) can hardly run > > > > > > into dirty pages for pageout(SYNC) unless in some race conditions. > > > > > > > > > > > > > > > > It's possible for the second call to run into dirty pages as there is a > > > > > congestion_wait() call between the first shrink_page_list() call and the > > > > > second. That's a big window. > > > > > > > > > > > And the wait page-by-page behavior of pageout(SYNC) will lead to very > > > > > > long stall time if running into some range of dirty pages. > > > > > > > > > > True, but this is also lumpy reclaim which is depending on a contiguous > > > > > range of pages. It's better for it to wait on the selected range of pages > > > > > which is known to contain at least one old page than excessively scan and > > > > > reclaim newer pages. > > > > > > > > Today, I was successful to reproduce the Andres's issue. and I disagree this > > > > opinion. > > > > > > Is Andres's issue not covered by the patch "vmscan: raise the bar to > > > PAGEOUT_IO_SYNC stalls" because wait_on_page_writeback() was the > > > main problem? > > > > Well, "vmscan: raise the bar to PAGEOUT_IO_SYNC stalls" is completely bandaid and > > No joking. The (DEF_PRIORITY-2) is obviously too permissive and shall be fixed. > > > much IO under slow USB flash memory device still cause such problem even if the patch is applied. > > As for this patch, raising the bar to PAGEOUT_IO_SYNC reduces both > calls to congestion_wait() and wait_on_page_writeback(). So it > absolutely helps by itself. > > > But removing wait_on_page_writeback() doesn't solve the issue perfectly because current > > lumpy reclaim have multiple sick. again, I'm writing explaining mail..... > > Let's submit the two known working fixes first? Definitely, I can't oppose obvious test result (by another your mail) :-) OK, should go! Thanks. -- 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