From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx128.postini.com [74.125.245.128]) by kanga.kvack.org (Postfix) with SMTP id 9AE426B004D for ; Tue, 4 Dec 2012 13:26:18 -0500 (EST) Date: Tue, 4 Dec 2012 18:17:56 +0000 From: Mel Gorman Subject: Re: [PATCH 2/2] mm/migration: Make rmap_walk_anon() and try_to_unmap_anon() more scalable Message-ID: <20121204143714.GB2797@suse.de> References: <1354305521-11583-1-git-send-email-mingo@kernel.org> <20121201094927.GA12366@gmail.com> <20121201122649.GA20322@gmail.com> <20121201184135.GA32449@gmail.com> <20121201201538.GB2704@gmail.com> <20121203141701.GN8218@suse.de> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-15 Content-Disposition: inline In-Reply-To: Sender: owner-linux-mm@kvack.org List-ID: To: Michel Lespinasse Cc: Ingo Molnar , Linus Torvalds , Linux Kernel Mailing List , linux-mm , Peter Zijlstra , Paul Turner , Lee Schermerhorn , Christoph Lameter , Rik van Riel , Andrew Morton , Andrea Arcangeli , Thomas Gleixner , Johannes Weiner , Hugh Dickins On Tue, Dec 04, 2012 at 06:37:41AM -0800, Michel Lespinasse wrote: > On Mon, Dec 3, 2012 at 6:17 AM, Mel Gorman wrote: > > On Sat, Dec 01, 2012 at 09:15:38PM +0100, Ingo Molnar wrote: > >> @@ -732,7 +732,7 @@ static int page_referenced_anon(struct p > >> struct anon_vma_chain *avc; > >> int referenced = 0; > >> > >> - anon_vma = page_lock_anon_vma(page); > >> + anon_vma = page_lock_anon_vma_read(page); > >> if (!anon_vma) > >> return referenced; > > > > This is a slightly trickier one as this path is called from reclaim. It does > > open the possibility that reclaim can stall something like a parallel fork > > or anything that requires the anon_vma rwsem for a period of time. I very > > severely doubt it'll really be a problem but keep an eye out for bug reports > > related to delayed mmap/fork/anything_needing_write_lock during page reclaim. > > I don't see why this would be a problem - rwsem does implement > reader/writer fairness, so having some sites do a read lock instead of > a write lock shouldn't cause the write lock sites to starve. Is this > what you were worried about ? > Yes. I did not expect they would be starved forever, just delayed longer than they might have been before. I would be very surprised if there is anything other than a synthetic case that will really care but I've been "very surprised" before :) -- Mel Gorman SUSE Labs -- 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