From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754074Ab2LMTG2 (ORCPT ); Thu, 13 Dec 2012 14:06:28 -0500 Received: from zene.cmpxchg.org ([85.214.230.12]:36276 "EHLO zene.cmpxchg.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750755Ab2LMTG1 (ORCPT ); Thu, 13 Dec 2012 14:06:27 -0500 Date: Thu, 13 Dec 2012 14:05:34 -0500 From: Johannes Weiner To: Mel Gorman Cc: Andrew Morton , Rik van Riel , Michal Hocko , Hugh Dickins , linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [patch 2/8] mm: vmscan: disregard swappiness shortly before going OOM Message-ID: <20121213190534.GA6317@cmpxchg.org> References: <1355348620-9382-1-git-send-email-hannes@cmpxchg.org> <1355348620-9382-3-git-send-email-hannes@cmpxchg.org> <20121213103420.GW1009@suse.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20121213103420.GW1009@suse.de> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Dec 13, 2012 at 10:34:20AM +0000, Mel Gorman wrote: > On Wed, Dec 12, 2012 at 04:43:34PM -0500, Johannes Weiner wrote: > > When a reclaim scanner is doing its final scan before giving up and > > there is swap space available, pay no attention to swappiness > > preference anymore. Just swap. > > > > Note that this change won't make too big of a difference for general > > reclaim: anonymous pages are already force-scanned when there is only > > very little file cache left, and there very likely isn't when the > > reclaimer enters this final cycle. > > > > Signed-off-by: Johannes Weiner > > Ok, I see the motivation for your patch but is the block inside still > wrong for what you want? After your patch the block looks like this > > if (sc->priority || noswap) { > scan >>= sc->priority; > if (!scan && force_scan) > scan = SWAP_CLUSTER_MAX; > scan = div64_u64(scan * fraction[file], denominator); > } > > if sc->priority == 0 and swappiness==0 then you enter this block but > fraction[0] for anonymous pages will also be 0 and because of the ordering > of statements there, scan will be > > scan = scan * 0 / denominator > > so you are still not reclaiming anonymous pages in the swappiness=0 > case. What did I miss? Don't get confused by noswap, it is only set when there physically is no swap space. If !sc->priority, that block is skipped and fraction[0] does not matter.