Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756022Ab0HAIgK (ORCPT ); Sun, 1 Aug 2010 04:36:10 -0400 Received: from mga11.intel.com ([192.55.52.93]:12956 "EHLO mga11.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753743Ab0HAIgI (ORCPT ); Sun, 1 Aug 2010 04:36:08 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="4.55,297,1278313200"; d="scan'208";a="823646179" Date: Sun, 1 Aug 2010 16:35:41 +0800 From: Wu Fengguang To: KOSAKI Motohiro Cc: 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 Subject: Re: [PATCH] vmscan: remove wait_on_page_writeback() from pageout() Message-ID: <20100801083541.GA14397@localhost> References: <20100728185457.4A82.A69D9226@jp.fujitsu.com> <20100801052758.GB7515@localhost> <20100801172600.4AFF.A69D9226@jp.fujitsu.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20100801172600.4AFF.A69D9226@jp.fujitsu.com> User-Agent: Mutt/1.5.20 (2009-06-14) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3301 Lines: 67 On Sun, Aug 01, 2010 at 04:32:01PM +0800, KOSAKI Motohiro wrote: > > 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! Great. Shall I go first? My changelog has more background :) Thanks, Fengguang -- 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/