Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754608Ab0G1KAB (ORCPT ); Wed, 28 Jul 2010 06:00:01 -0400 Received: from fgwmail6.fujitsu.co.jp ([192.51.44.36]:35104 "EHLO fgwmail6.fujitsu.co.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753806Ab0G1J77 (ORCPT ); Wed, 28 Jul 2010 05:59:59 -0400 X-SecurityPolicyCheck-FJ: OK by FujitsuOutboundMailChecker v1.3.1 From: KOSAKI Motohiro To: Mel Gorman Subject: Re: [PATCH] vmscan: remove wait_on_page_writeback() from pageout() Cc: kosaki.motohiro@jp.fujitsu.com, Wu Fengguang , 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 In-Reply-To: <20100728095058.GF5300@csn.ul.ie> References: <20100728183625.4A7F.A69D9226@jp.fujitsu.com> <20100728095058.GF5300@csn.ul.ie> Message-Id: <20100728185457.4A82.A69D9226@jp.fujitsu.com> MIME-Version: 1.0 Content-Type: text/plain; charset="US-ASCII" Content-Transfer-Encoding: 7bit X-Mailer: Becky! ver. 2.50.07 [ja] Date: Wed, 28 Jul 2010 18:59:55 +0900 (JST) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2414 Lines: 50 > 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 much IO under slow USB flash memory device still cause such problem even if the patch is applied. 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..... -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/