From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751256Ab1L0GHQ (ORCPT ); Tue, 27 Dec 2011 01:07:16 -0500 Received: from mho-02-ewr.mailhop.org ([204.13.248.72]:45235 "EHLO mho-02-ewr.mailhop.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750847Ab1L0GHN convert rfc822-to-8bit (ORCPT ); Tue, 27 Dec 2011 01:07:13 -0500 X-Mail-Handler: MailHop Outbound by DynDNS X-Originating-IP: 80.237.6.56 X-Report-Abuse-To: abuse@dyndns.com (see http://www.dyndns.com/services/mailhop/outbound_abuse.html for abuse reporting information) X-MHO-User: U2FsdGVkX1/eQhyc/MQxeucFKTK9bZMLBMFOQNr4lYQ= Message-ID: <1324966011.8894.1.camel@rybalov.eng.ttk.net> Subject: Re: Kswapd in 3.2.0-rc5 is a CPU hog From: nowhere To: KAMEZAWA Hiroyuki Cc: Dave Chinner , Michal Hocko , linux-kernel@vger.kernel.org, linux-mm@kvack.org Date: Tue, 27 Dec 2011 10:06:51 +0400 In-Reply-To: <20111227134405.9902dcbb.kamezawa.hiroyu@jp.fujitsu.com> References: <1324437036.4677.5.camel@hakkenden.homenet> <20111221095249.GA28474@tiehlicka.suse.cz> <20111221225512.GG23662@dastard> <1324630880.562.6.camel@rybalov.eng.ttk.net> <20111223102027.GB12731@dastard> <1324638242.562.15.camel@rybalov.eng.ttk.net> <20111223204503.GC12731@dastard> <20111227111543.5e486eb7.kamezawa.hiroyu@jp.fujitsu.com> <1324954208.4634.2.camel@hakkenden.homenet> <20111227134405.9902dcbb.kamezawa.hiroyu@jp.fujitsu.com> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.2.2 Content-Transfer-Encoding: 8BIT Mime-Version: 1.0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org В Вт., 27/12/2011 в 13:44 +0900, KAMEZAWA Hiroyuki пишет: > On Tue, 27 Dec 2011 06:50:08 +0400 > "Nikolay S." wrote: > > > В Вт., 27/12/2011 в 11:15 +0900, KAMEZAWA Hiroyuki пишет: > > > On Sat, 24 Dec 2011 07:45:03 +1100 > > > Dave Chinner wrote: > > > > > > > On Fri, Dec 23, 2011 at 03:04:02PM +0400, nowhere wrote: > > > > > В Пт., 23/12/2011 в 21:20 +1100, Dave Chinner пишет: > > > > > > On Fri, Dec 23, 2011 at 01:01:20PM +0400, nowhere wrote: > > > > > > > В Чт., 22/12/2011 в 09:55 +1100, Dave Chinner пишет: > > > > > > > > On Wed, Dec 21, 2011 at 10:52:49AM +0100, Michal Hocko wrote: > > > > > > > > Here is the report of trace-cmd while dd'ing > > > > > https://80.237.6.56/report-dd.xz > > > > > > > > Ok, it's not a shrink_slab() problem - it's just being called ~100uS > > > > by kswapd. The pattern is: > > > > > > > > - reclaim 94 (batches of 32,32,30) pages from iinactive list > > > > of zone 1, node 0, prio 12 > > > > - call shrink_slab > > > > - scan all caches > > > > - all shrinkers return 0 saying nothing to shrink > > > > - 40us gap > > > > - reclaim 10-30 pages from inactive list of zone 2, node 0, prio 12 > > > > - call shrink_slab > > > > - scan all caches > > > > - all shrinkers return 0 saying nothing to shrink > > > > - 40us gap > > > > - isolate 9 pages from LRU zone ?, node ?, none isolated, none freed > > > > - isolate 22 pages from LRU zone ?, node ?, none isolated, none freed > > > > - call shrink_slab > > > > - scan all caches > > > > - all shrinkers return 0 saying nothing to shrink > > > > 40us gap > > > > > > > > And it just repeats over and over again. After a while, nid=0,zone=1 > > > > drops out of the traces, so reclaim only comes in batches of 10-30 > > > > pages from zone 2 between each shrink_slab() call. > > > > > > > > The trace starts at 111209.881s, with 944776 pages on the LRUs. It > > > > finishes at 111216.1 with kswapd going to sleep on node 0 with > > > > 930067 pages on the LRU. So 7 seconds to free 15,000 pages (call it > > > > 2,000 pages/s) which is awfully slow.... > > > > > > > > vmscan gurus - time for you to step in now... > > > > > > > > > > Can you show /proc/zoneinfo ? I want to know each zone's size. > > > > Thanks, > Qeustion: > 1. does this system has no swap ? It has. 4G > 2. What version of kernel which you didn't see the kswapd issue ? Hmm... 3.1 and below, I presume > 3. Is this real host ? or virtualized ? 100% real > > > $ cat /proc/zoneinfo > ... > Node 0, zone DMA32 > pages free 19620 > min 14715 > low 18393 > high 22072 > scanned 0 > spanned 1044480 > present 896960 > nr_free_pages 19620 > nr_inactive_anon 43203 > nr_active_anon 206577 > nr_inactive_file 412249 > nr_active_file 126151 > > Then, DMA32(zone=1) files are enough large (> 32 << 12) > Hmm. assuming all frees are used for file(of dd) > > > (412249 + 126151 + 19620) >> 12 = 136 > > So, 32, 32, 30 scan seems to work as desgined. > > > Node 0, zone Normal > > pages free 2854 > > min 2116 > > low 2645 > > high 3174 > > scanned 0 > > spanned 131072 > > present 129024 > > nr_free_pages 2854 > > nr_inactive_anon 20682 > > nr_active_anon 10262 > > nr_inactive_file 47083 > > nr_active_file 11292 > > Hmm, NORMAL is much smaller than DMA32. (only 500MB.) > > Then, at priority=12, > > 13 << 12 = 53248 > > 13 pages per a scan seems to work as designed. > To me, it seems kswapd does usual work...reclaim small memory until free > gets enough. And it seems 'dd' allocates its memory from ZONE_DMA32 because > of gfp_t fallbacks. > > > Memo. > > 1. why shrink_slab() should be called per zone, which is not zone aware. > Isn't it enough to call it per priority ? > > 2. what spinlock contention that perf showed ? > And if shrink_slab() doesn't consume cpu as trace shows, why perf > says shrink_slab() is heavy.. > > 3. because 8/9 of memory is in DMA32, calling shrink_slab() frequently > at scanning NORMAL seems to be time wasting. > > > Thanks, > -Kame > > > > >