Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755342AbZFUSlT (ORCPT ); Sun, 21 Jun 2009 14:41:19 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752303AbZFUSlM (ORCPT ); Sun, 21 Jun 2009 14:41:12 -0400 Received: from cmpxchg.org ([85.214.51.133]:45959 "EHLO cmpxchg.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751423AbZFUSlM (ORCPT ); Sun, 21 Jun 2009 14:41:12 -0400 Date: Sun, 21 Jun 2009 20:37:30 +0200 From: Johannes Weiner To: Hugh Dickins Cc: Wu Fengguang , "Barnes, Jesse" , Peter Zijlstra , KAMEZAWA Hiroyuki , Andrew Morton , Rik van Riel , Andi Kleen , Minchan Kim , "linux-mm@kvack.org" , "linux-kernel@vger.kernel.org" Subject: Re: [patch v3] swap: virtual swap readahead Message-ID: <20090621183730.GA4796@cmpxchg.org> References: <1244628314.13761.11617.camel@twins> <20090610113214.GA5657@localhost> <20090610102516.08f7300f@jbarnes-x200> <20090611052228.GA20100@localhost> <20090611101741.GA1974@cmpxchg.org> <20090612015927.GA6804@localhost> <20090615182216.GA1661@cmpxchg.org> <20090618091949.GA711@localhost> <20090618130121.GA1817@cmpxchg.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2266 Lines: 55 On Sun, Jun 21, 2009 at 07:07:03PM +0100, Hugh Dickins wrote: > Hi Hannes, > > On Thu, 18 Jun 2009, Johannes Weiner wrote: > > On Thu, Jun 18, 2009 at 05:19:49PM +0800, Wu Fengguang wrote: > > > > Okay, evaluating this test-patch any further probably isn't worth it. > > It's too aggressive, I think readahead is stealing pages reclaimed by > > other allocations which in turn oom. > > > > Back to the original problem: you detected increased latency for > > launching new applications, so they get less share of the IO bandwidth > > than without the patch. > > > > I can see two reasons for this: > > > > a) the new heuristics don't work out and we read more unrelated > > pages than before > > > > b) we readahead more pages in total as the old code would stop at > > holes, as described above > > > > We can verify a) by comparing major fault numbers between the two > > kernels with your testload. If they increase with my patch, we > > anticipate the wrong slots and every fault has do the reading itself. > > > > b) seems to be a trade-off. After all, the IO resources you have less > > for new applications in your test is the bandwidth that is used by > > swapping applications. My qsbench numbers are a sign for this as the > > only IO going on is swap. > > > > Of course, the theory is not to improve swap performance by increasing > > the readahead window but to choose better readahead candidates. So I > > will run your tests and qsbench with a smaller page cluster and see if > > this improves both loads. > > Hmm, sounds rather pessimistic; but I've not decided about it either. It seems the problem was not that real after all: http://lkml.org/lkml/2009/6/18/109 > May I please hand over to you this collection of adjustments to your > v3 virtual swap readahead patch, for you to merge in or split up or > mess around with, generally take ownership of, however you wish? > So you can keep adjusting shmem.c to match memory.c if necessary. I will adopt them, thank you! Hannes -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/