From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail172.messagelabs.com (mail172.messagelabs.com [216.82.254.3]) by kanga.kvack.org (Postfix) with SMTP id 534EA6B0044 for ; Wed, 16 Dec 2009 00:43:49 -0500 (EST) Subject: Re: [PATCH 4/8] Use prepare_to_wait_exclusive() instead prepare_to_wait() From: Mike Galbraith In-Reply-To: <20091216093533.CDF1.A69D9226@jp.fujitsu.com> References: <1260855146.6126.30.camel@marge.simson.net> <4B27A417.3040206@redhat.com> <20091216093533.CDF1.A69D9226@jp.fujitsu.com> Content-Type: text/plain Date: Wed, 16 Dec 2009 06:43:44 +0100 Message-Id: <1260942224.5766.57.camel@marge.simson.net> Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org To: KOSAKI Motohiro Cc: Rik van Riel , lwoodman@redhat.com, akpm@linux-foundation.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, minchan.kim@gmail.com List-ID: On Wed, 2009-12-16 at 09:48 +0900, KOSAKI Motohiro wrote: > > 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. Along those lines, there's also NEWIDLE balancing considerations. That idle may result in a task being pulled, which may or may not hurt a bit. 'course, if you're jamming up on memory allocation, that's the least of your worries, but every idle avoided is potentially a pull avoided. Just a thought. -Mike -- 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