Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757695AbZLPAtI (ORCPT ); Tue, 15 Dec 2009 19:49:08 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1754376AbZLPAs7 (ORCPT ); Tue, 15 Dec 2009 19:48:59 -0500 Received: from fgwmail5.fujitsu.co.jp ([192.51.44.35]:41847 "EHLO fgwmail5.fujitsu.co.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754206AbZLPAs5 (ORCPT ); Tue, 15 Dec 2009 19:48:57 -0500 X-SecurityPolicyCheck-FJ: OK by FujitsuOutboundMailChecker v1.3.1 From: KOSAKI Motohiro To: Rik van Riel Subject: Re: [PATCH 4/8] Use prepare_to_wait_exclusive() instead prepare_to_wait() Cc: kosaki.motohiro@jp.fujitsu.com, Mike Galbraith , lwoodman@redhat.com, akpm@linux-foundation.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, minchan.kim@gmail.com In-Reply-To: <4B27A417.3040206@redhat.com> References: <1260855146.6126.30.camel@marge.simson.net> <4B27A417.3040206@redhat.com> Message-Id: <20091216093533.CDF1.A69D9226@jp.fujitsu.com> MIME-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 8bit X-Mailer: Becky! ver. 2.50.07 [ja] Date: Wed, 16 Dec 2009 09:48:51 +0900 (JST) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2100 Lines: 55 > On 12/15/2009 12:32 AM, Mike Galbraith wrote: > > On Tue, 2009-12-15 at 09:45 +0900, KOSAKI Motohiro wrote: > >>> On 12/14/2009 07:30 AM, KOSAKI Motohiro wrote: > >>>> if we don't use exclusive queue, wake_up() function wake _all_ waited > >>>> task. This is simply cpu wasting. > >>>> > >>>> Signed-off-by: KOSAKI Motohiro > >>> > >>>> if (zone_watermark_ok(zone, sc->order, low_wmark_pages(zone), > >>>> 0, 0)) { > >>>> - wake_up(wq); > >>>> + wake_up_all(wq); > >>>> finish_wait(wq,&wait); > >>>> sc->nr_reclaimed += sc->nr_to_reclaim; > >>>> return -ERESTARTSYS; > >>> > >>> I believe we want to wake the processes up one at a time > >>> here. > > >> Actually, wake_up() and wake_up_all() aren't different so much. > >> Although we use wake_up(), the task wake up next task before > >> try to alloate memory. then, it's similar to wake_up_all(). > > That is a good point. Maybe processes need to wait a little > in this if() condition, before the wake_up(). That would give > the previous process a chance to allocate memory and we can > avoid waking up too many processes. if we really need wait a bit, Mike's wake_up_batch is best, I think. It mean - if another CPU is idle, wake up one process soon. iow, it don't make meaningless idle. - if another CPU is busy, woken process don't start to run awhile. then, zone_watermark_ok() can calculate correct value. > > What happens to waiters should running tasks not allocate for a while? > > When a waiter is woken up, it will either: > 1) see that there is enough free memory and wake up the next guy, or > 2) run shrink_zone and wake up the next guy > > Either way, the processes that just got woken up will ensure that > the sleepers behind them in the queue will get woken up. > > -- > All rights reversed. -- 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/