Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758503Ab1D2C2z (ORCPT ); Thu, 28 Apr 2011 22:28:55 -0400 Received: from mga09.intel.com ([134.134.136.24]:29243 "EHLO mga09.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757403Ab1D2C23 (ORCPT ); Thu, 28 Apr 2011 22:28:29 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="4.64,284,1301900400"; d="scan'208";a="739989269" Date: Fri, 29 Apr 2011 10:28:24 +0800 From: Wu Fengguang To: Andrew Morton Cc: Minchan Kim , Dave Young , linux-mm , Linux Kernel Mailing List , Mel Gorman , KAMEZAWA Hiroyuki , KOSAKI Motohiro , Christoph Lameter , Dave Chinner , David Rientjes Subject: Re: [RFC][PATCH] mm: cut down __GFP_NORETRY page allocation failures Message-ID: <20110429022824.GA8061@localhost> References: <20110426055521.GA18473@localhost> <20110426062535.GB19717@localhost> <20110426063421.GC19717@localhost> <20110426092029.GA27053@localhost> <20110426124743.e58d9746.akpm@linux-foundation.org> <20110428133644.GA12400@localhost> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20110428133644.GA12400@localhost> User-Agent: Mutt/1.5.20 (2009-06-14) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 7140 Lines: 230 > Test results: > > - the failure rate is pretty sensible to the page reclaim size, > from 282 (WMARK_HIGH) to 704 (WMARK_MIN) to 10496 (SWAP_CLUSTER_MAX) > > - the IPIs are reduced by over 100 times It's reduced by 500 times indeed. CAL: 220449 220246 220372 220558 220251 219740 220043 219968 Function call interrupts CAL: 93 463 410 540 298 282 272 306 Function call interrupts > base kernel: vanilla 2.6.39-rc3 + __GFP_NORETRY readahead page allocation patch > ------------------------------------------------------------------------------- > nr_alloc_fail 10496 > allocstall 1576602 > patched (WMARK_MIN) > ------------------- > nr_alloc_fail 704 > allocstall 105551 > patched (WMARK_HIGH) > -------------------- > nr_alloc_fail 282 > allocstall 53860 > this patch (WMARK_HIGH, limited scan) > ------------------------------------- > nr_alloc_fail 276 > allocstall 54034 There is a bad side effect though: the much reduced "allocstall" means each direct reclaim will take much more time to complete. A simple solution is to terminate direct reclaim after 10ms. I noticed that an 100ms time threshold can reduce the reclaim latency from 621ms to 358ms. Further lowering the time threshold to 20ms does not help reducing the real latencies though. However the very subjective perception is, in such heavy 1000-dd workload, the reduced reclaim latency hardly improves the overall responsiveness. base kernel ----------- start time: 243 total time: 529 wfg@fat ~% getdelays -dip 3971 print delayacct stats ON printing IO accounting PID 3971 CPU count real total virtual total delay total 961 3176517096 3158468847 313952766099 IO count delay total delay average 2 181251847 60ms SWAP count delay total delay average 0 0 0ms RECLAIM count delay total delay average 1205 38120615476 31ms dd: read=16384, write=0, cancelled_write=0 wfg@fat ~% getdelays -dip 3383 print delayacct stats ON printing IO accounting PID 3383 CPU count real total virtual total delay total 1270 4206360536 4181445838 358641985177 IO count delay total delay average 0 0 0ms SWAP count delay total delay average 0 0 0ms RECLAIM count delay total delay average 1606 39897314399 24ms dd: read=0, write=0, cancelled_write=0 no time limit ------------- wfg@fat ~% getdelays -dip `pidof dd` print delayacct stats ON printing IO accounting PID 9609 CPU count real total virtual total delay total 865 2792575464 2779071029 235345541230 IO count delay total delay average 4 300247552 60ms SWAP count delay total delay average 0 0 0ms RECLAIM count delay total delay average 32 20504634169 621ms dd: read=106496, write=0, cancelled_write=0 100ms limit ----------- start time: 288 total time: 514 nr_alloc_fail 1269 allocstall 128915 wfg@fat ~% getdelays -dip `pidof dd` print delayacct stats ON printing IO accounting PID 5077 CPU count real total virtual total delay total 937 2949551600 2935087806 207877301298 IO count delay total delay average 1 151891691 151ms SWAP count delay total delay average 0 0 0ms RECLAIM count delay total delay average 71 25475514278 358ms dd: read=507904, write=0, cancelled_write=0 PID 5101 CPU count real total virtual total delay total 1201 3827418144 3805399187 221075772599 IO count delay total delay average 4 300331997 60ms SWAP count delay total delay average 0 0 0ms RECLAIM count delay total delay average 94 31996779648 336ms dd: read=618496, write=0, cancelled_write=0 nr_alloc_fail 937 allocstall 128684 slabs_scanned 63616 kswapd_steal 4616011 kswapd_inodesteal 5 kswapd_low_wmark_hit_quickly 5394 kswapd_high_wmark_hit_quickly 2826 kswapd_skip_congestion_wait 0 pageoutrun 36679 20ms limit ---------- start time: 294 total time: 516 nr_alloc_fail 1662 allocstall 132101 CPU count real total virtual total delay total 839 2750581848 2734464704 198489159459 IO count delay total delay average 1 43566814 43ms SWAP count delay total delay average 0 0 0ms RECLAIM count delay total delay average 95 35234061367 370ms dd: read=20480, write=0, cancelled_write=0 test script ----------- tic=$(date +'%s') for i in `seq 1000` do truncate -s 1G /fs/sparse-$i dd if=/fs/sparse-$i of=/dev/null &>/dev/null & done tac=$(date +'%s') echo start time: $((tac-tic)) wait tac=$(date +'%s') echo total time: $((tac-tic)) egrep '(nr_alloc_fail|allocstall)' /proc/vmstat Thanks, Fengguang --- Subject: mm: limit direct reclaim delays Date: Fri Apr 29 09:04:11 CST 2011 Signed-off-by: Wu Fengguang --- mm/vmscan.c | 14 +++++++++----- 1 file changed, 9 insertions(+), 5 deletions(-) --- linux-next.orig/mm/vmscan.c 2011-04-29 09:02:42.000000000 +0800 +++ linux-next/mm/vmscan.c 2011-04-29 09:04:10.000000000 +0800 @@ -2037,6 +2037,7 @@ static unsigned long do_try_to_free_page struct zone *zone; unsigned long writeback_threshold; unsigned long min_reclaim = sc->nr_to_reclaim; + unsigned long start_time = jiffies; get_mems_allowed(); delayacct_freepages_start(); @@ -2070,11 +2071,14 @@ static unsigned long do_try_to_free_page } } total_scanned += sc->nr_scanned; - if (sc->nr_reclaimed >= min_reclaim && - total_scanned > 2 * sc->nr_to_reclaim) - goto out; - if (sc->nr_reclaimed >= sc->nr_to_reclaim) - goto out; + if (sc->nr_reclaimed >= min_reclaim) { + if (sc->nr_reclaimed >= sc->nr_to_reclaim) + goto out; + if (total_scanned > 2 * sc->nr_to_reclaim) + goto out; + if (jiffies - start_time > HZ / 100) + goto out; + } /* * Try to write back as many pages as we just scanned. 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