From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail144.messagelabs.com (mail144.messagelabs.com [216.82.254.51]) by kanga.kvack.org (Postfix) with SMTP id AF1A16B0044 for ; Mon, 14 Dec 2009 19:45:31 -0500 (EST) Received: from m1.gw.fujitsu.co.jp ([10.0.50.71]) by fgwmail7.fujitsu.co.jp (Fujitsu Gateway) with ESMTP id nBF0jTOt012915 for (envelope-from kosaki.motohiro@jp.fujitsu.com); Tue, 15 Dec 2009 09:45:29 +0900 Received: from smail (m1 [127.0.0.1]) by outgoing.m1.gw.fujitsu.co.jp (Postfix) with ESMTP id 4E67A45DE59 for ; Tue, 15 Dec 2009 09:45:29 +0900 (JST) Received: from s1.gw.fujitsu.co.jp (s1.gw.fujitsu.co.jp [10.0.50.91]) by m1.gw.fujitsu.co.jp (Postfix) with ESMTP id 292EA45DE51 for ; Tue, 15 Dec 2009 09:45:29 +0900 (JST) Received: from s1.gw.fujitsu.co.jp (localhost.localdomain [127.0.0.1]) by s1.gw.fujitsu.co.jp (Postfix) with ESMTP id 0CD1E1DB8046 for ; Tue, 15 Dec 2009 09:45:29 +0900 (JST) Received: from ml13.s.css.fujitsu.com (ml13.s.css.fujitsu.com [10.249.87.103]) by s1.gw.fujitsu.co.jp (Postfix) with ESMTP id B26781DB8043 for ; Tue, 15 Dec 2009 09:45:28 +0900 (JST) From: KOSAKI Motohiro Subject: Re: [PATCH 4/8] Use prepare_to_wait_exclusive() instead prepare_to_wait() In-Reply-To: <4B264CCA.5010609@redhat.com> References: <20091214212936.BBBA.A69D9226@jp.fujitsu.com> <4B264CCA.5010609@redhat.com> Message-Id: <20091215085631.CDAD.A69D9226@jp.fujitsu.com> MIME-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 8bit Date: Tue, 15 Dec 2009 09:45:27 +0900 (JST) Sender: owner-linux-mm@kvack.org To: Rik van Riel Cc: kosaki.motohiro@jp.fujitsu.com, lwoodman@redhat.com, akpm@linux-foundation.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, minchan.kim@gmail.com List-ID: > 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. If the queue of waiting processes is very large > and the amount of excess free memory is fairly low, the > first processes that wake up can take the amount of free > memory back down below the threshold. The rest of the > waiters should stay asleep when this happens. OK. 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(). However, there are few difference. recent scheduler latency improvement effort reduce default scheduler latency target. it mean, if we have lots tasks of running state, the task have very few time slice. too frequently context switch decrease VM efficiency. Thank you, Rik. I didn't notice wake_up() makes better performance than wake_up_all() on current kernel. Subject: [PATCH 9/8] replace wake_up_all with wake_up Fix typo. Signed-off-by: KOSAKI Motohiro --- mm/vmscan.c | 2 +- 1 files changed, 1 insertions(+), 1 deletions(-) diff --git a/mm/vmscan.c b/mm/vmscan.c index e5adb7a..b3b4e77 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -1644,7 +1644,7 @@ static int shrink_zone_begin(struct zone *zone, struct scan_control *sc) return 0; found_lots_memory: - wake_up_all(wq); + wake_up(wq); stop_reclaim: finish_wait(wq, &wait); sc->nr_reclaimed += sc->nr_to_reclaim; -- 1.6.5.2 -- 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