From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756757Ab0IPW2v (ORCPT ); Thu, 16 Sep 2010 18:28:51 -0400 Received: from smtp1.linux-foundation.org ([140.211.169.13]:50102 "EHLO smtp1.linux-foundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753877Ab0IPW2u (ORCPT ); Thu, 16 Sep 2010 18:28:50 -0400 Date: Thu, 16 Sep 2010 15:28:10 -0700 From: Andrew Morton To: Mel Gorman Cc: linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, Linux Kernel List , Johannes Weiner , Minchan Kim , Wu Fengguang , KAMEZAWA Hiroyuki , KOSAKI Motohiro Subject: Re: [PATCH 8/8] writeback: Do not sleep on the congestion queue if there are no congested BDIs or if significant congestion is not being encountered in the current zone Message-Id: <20100916152810.cb074e9f.akpm@linux-foundation.org> In-Reply-To: <1284553671-31574-9-git-send-email-mel@csn.ul.ie> References: <1284553671-31574-1-git-send-email-mel@csn.ul.ie> <1284553671-31574-9-git-send-email-mel@csn.ul.ie> X-Mailer: Sylpheed 2.4.8 (GTK+ 2.12.9; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 15 Sep 2010 13:27:51 +0100 Mel Gorman wrote: > If wait_iff_congested() is called with no BDI congested, the function simply > calls cond_resched(). In the event there is significant writeback happening > in the zone that is being reclaimed, this can be a poor decision as reclaim > would succeed once writeback was completed. Without any backoff logic, > younger clean pages can be reclaimed resulting in more reclaim overall and > poor performance. This is because cond_resched() is a no-op, and we skip around the under-writeback pages and go off and look further along the LRU for younger clean pages, yes? > This patch tracks how many pages backed by a congested BDI were found during > scanning. If all the dirty pages encountered on a list isolated from the > LRU belong to a congested BDI, the zone is marked congested until the zone > reaches the high watermark. High watermark, or low watermark? The terms are rather ambiguous so let's avoid them. Maybe "full" watermark and "empty"? > > ... > > @@ -706,6 +726,7 @@ static unsigned long shrink_page_list(struct list_head *page_list, > goto keep; > > VM_BUG_ON(PageActive(page)); > + VM_BUG_ON(page_zone(page) != zone); ? > sc->nr_scanned++; > > > ... > > @@ -903,6 +928,15 @@ keep_lumpy: > VM_BUG_ON(PageLRU(page) || PageUnevictable(page)); > } > > + /* > + * Tag a zone as congested if all the dirty pages encountered were > + * backed by a congested BDI. In this case, reclaimers should just > + * back off and wait for congestion to clear because further reclaim > + * will encounter the same problem > + */ > + if (nr_dirty == nr_congested) > + zone_set_flag(zone, ZONE_CONGESTED); The implicit "100%" there is a magic number. hrm. From mboxrd@z Thu Jan 1 00:00:00 1970 From: Andrew Morton Subject: Re: [PATCH 8/8] writeback: Do not sleep on the congestion queue if there are no congested BDIs or if significant congestion is not being encountered in the current zone Date: Thu, 16 Sep 2010 15:28:10 -0700 Message-ID: <20100916152810.cb074e9f.akpm@linux-foundation.org> References: <1284553671-31574-1-git-send-email-mel@csn.ul.ie> <1284553671-31574-9-git-send-email-mel@csn.ul.ie> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Cc: linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, Linux Kernel List , Johannes Weiner , Minchan Kim , Wu Fengguang , KAMEZAWA Hiroyuki , KOSAKI Motohiro To: Mel Gorman Return-path: In-Reply-To: <1284553671-31574-9-git-send-email-mel@csn.ul.ie> Sender: owner-linux-mm@kvack.org List-Id: linux-fsdevel.vger.kernel.org On Wed, 15 Sep 2010 13:27:51 +0100 Mel Gorman wrote: > If wait_iff_congested() is called with no BDI congested, the function simply > calls cond_resched(). In the event there is significant writeback happening > in the zone that is being reclaimed, this can be a poor decision as reclaim > would succeed once writeback was completed. Without any backoff logic, > younger clean pages can be reclaimed resulting in more reclaim overall and > poor performance. This is because cond_resched() is a no-op, and we skip around the under-writeback pages and go off and look further along the LRU for younger clean pages, yes? > This patch tracks how many pages backed by a congested BDI were found during > scanning. If all the dirty pages encountered on a list isolated from the > LRU belong to a congested BDI, the zone is marked congested until the zone > reaches the high watermark. High watermark, or low watermark? The terms are rather ambiguous so let's avoid them. Maybe "full" watermark and "empty"? > > ... > > @@ -706,6 +726,7 @@ static unsigned long shrink_page_list(struct list_head *page_list, > goto keep; > > VM_BUG_ON(PageActive(page)); > + VM_BUG_ON(page_zone(page) != zone); ? > sc->nr_scanned++; > > > ... > > @@ -903,6 +928,15 @@ keep_lumpy: > VM_BUG_ON(PageLRU(page) || PageUnevictable(page)); > } > > + /* > + * Tag a zone as congested if all the dirty pages encountered were > + * backed by a congested BDI. In this case, reclaimers should just > + * back off and wait for congestion to clear because further reclaim > + * will encounter the same problem > + */ > + if (nr_dirty == nr_congested) > + zone_set_flag(zone, ZONE_CONGESTED); The implicit "100%" there is a magic number. hrm. -- 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