Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753265Ab0HZRiw (ORCPT ); Thu, 26 Aug 2010 13:38:52 -0400 Received: from mail-pv0-f174.google.com ([74.125.83.174]:59032 "EHLO mail-pv0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753172Ab0HZRiv (ORCPT ); Thu, 26 Aug 2010 13:38:51 -0400 DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=date:from:to:cc:subject:message-id:references:mime-version :content-type:content-disposition:in-reply-to:user-agent; b=cCDA64l2i1gvQx08M2lL3BpmADbstIIioG0XJbCyj0r1nYY9bRZ53wSLgdeRXVMEXX NLI44btSUorl2iM3xFjb+NytiGDnSJvxzAev1RH+hCe5FLF/w/vgdxnr4KHKprYG/BYn SBaFhytWyUaGC515VDIyRpmOPvIj4wWSLjivE= Date: Fri, 27 Aug 2010 02:38:43 +0900 From: Minchan Kim To: Mel Gorman Cc: linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, Andrew Morton , Christian Ehrhardt , Johannes Weiner , Wu Fengguang , Jan Kara , linux-kernel@vger.kernel.org Subject: Re: [PATCH 3/3] writeback: Do not congestion sleep when there are no congested BDIs Message-ID: <20100826173843.GD6873@barrios-desktop> References: <1282835656-5638-1-git-send-email-mel@csn.ul.ie> <1282835656-5638-4-git-send-email-mel@csn.ul.ie> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1282835656-5638-4-git-send-email-mel@csn.ul.ie> 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: 2858 Lines: 76 On Thu, Aug 26, 2010 at 04:14:16PM +0100, Mel Gorman wrote: > If congestion_wait() is called with no BDIs congested, the caller will > sleep for the full timeout and this is an unnecessary sleep. This patch > checks if there are BDIs congested. If so, it goes to sleep as normal. > If not, it calls cond_resched() to ensure the caller is not hogging the > CPU longer than its quota but otherwise will not sleep. > > This is aimed at reducing some of the major desktop stalls reported during > IO. For example, while kswapd is operating, it calls congestion_wait() > but it could just have been reclaiming clean page cache pages with no > congestion. Without this patch, it would sleep for a full timeout but after > this patch, it'll just call schedule() if it has been on the CPU too long. > Similar logic applies to direct reclaimers that are not making enough > progress. > > Signed-off-by: Mel Gorman > --- > mm/backing-dev.c | 20 ++++++++++++++------ > 1 files changed, 14 insertions(+), 6 deletions(-) > > diff --git a/mm/backing-dev.c b/mm/backing-dev.c > index a49167f..6abe860 100644 > --- a/mm/backing-dev.c > +++ b/mm/backing-dev.c Function's decripton should be changed since we don't wait next write any more. > @@ -767,13 +767,21 @@ long congestion_wait(int sync, long timeout) > DEFINE_WAIT(wait); > wait_queue_head_t *wqh = &congestion_wqh[sync]; > > - /* Check if this call to congestion_wait was necessary */ > - if (atomic_read(&nr_bdi_congested[sync]) == 0) > + /* > + * If there is no congestion, there is no point sleeping on the queue. > + * This call was unecessary but in case we are spinning due to a bad > + * caller, at least call cond_reched() and sleep if our CPU quota > + * has expired > + */ > + if (atomic_read(&nr_bdi_congested[sync]) == 0) { > unnecessary = true; > - > - prepare_to_wait(wqh, &wait, TASK_UNINTERRUPTIBLE); > - ret = io_schedule_timeout(timeout); > - finish_wait(wqh, &wait); > + cond_resched(); > + ret = 0; "ret = timeout" is more proper as considering io_schedule_timeout's return value. > + } else { > + prepare_to_wait(wqh, &wait, TASK_UNINTERRUPTIBLE); > + ret = io_schedule_timeout(timeout); > + finish_wait(wqh, &wait); > + } > > trace_writeback_congest_waited(jiffies_to_usecs(jiffies - start), > unnecessary); > -- > 1.7.1 > > -- > 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 > -- Kind regards, Minchan Kim -- 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/