From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx134.postini.com [74.125.245.134]) by kanga.kvack.org (Postfix) with SMTP id B313E6B005A for ; Thu, 6 Sep 2012 08:57:54 -0400 (EDT) Received: by pbbro12 with SMTP id ro12so2732865pbb.14 for ; Thu, 06 Sep 2012 05:57:54 -0700 (PDT) Date: Thu, 6 Sep 2012 20:57:41 +0800 From: Shaohua Li Subject: Re: [patch 2/2]compaction: check lock contention first before taking lock Message-ID: <20120906125741.GB1025@kernel.org> References: <20120906104429.GB12718@kernel.org> <20120906122449.GR11266@suse.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20120906122449.GR11266@suse.de> Sender: owner-linux-mm@kvack.org List-ID: To: Mel Gorman Cc: linux-mm@kvack.org, akpm@linux-foundation.org, aarcange@redhat.com On Thu, Sep 06, 2012 at 01:24:49PM +0100, Mel Gorman wrote: > On Thu, Sep 06, 2012 at 06:44:29PM +0800, Shaohua Li wrote: > > isolate_migratepages_range will take zone->lru_lock first and check if the lock > > is contented, if yes, it will release the lock. This isn't efficient. If the > > lock is truly contented, a lock/unlock pair will increase the lock contention. > > We'd better check if the lock is contended first. compact_trylock_irqsave > > perfectly meets the requirement. > > > > Signed-off-by: Shaohua Li > > --- > > mm/compaction.c | 7 ++++--- > > 1 file changed, 4 insertions(+), 3 deletions(-) > > > > Index: linux/mm/compaction.c > > =================================================================== > > --- linux.orig/mm/compaction.c 2012-09-06 14:46:13.923144263 +0800 > > +++ linux/mm/compaction.c 2012-09-06 14:46:58.118588574 +0800 > > @@ -295,9 +295,9 @@ isolate_migratepages_range(struct zone * > > } > > > > /* Time to isolate some pages for migration */ > > - cond_resched(); > > Why did you remove the cond_resched()? I expect it's because > compact_checklock_irqsave() does a need_resched() check and if it is true > will either call cond_resched() or abort compaction. If it is aborting it > will not call cond_resched() but there is a reasonable expectation that > the caller will schedule soon. If this is the reasoning then it should be > included in the changelog. If it's an accident then leave the cond_resched() > where it is. Ok, looks I overlooked at it, will change it in next post. > > - spin_lock_irqsave(&zone->lru_lock, flags); > > - locked = true; > > + locked = compact_trylock_irqsave(&zone->lru_lock, &flags, cc); > > + if (!locked) > > + goto skip; > > There is no need for the goto. No useful work has taken place at this > point and there is no need to even trigger the tracepoint. Just return > 0. Just want to print out something in trace, but that's fine, I'll fix this. -- 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