Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756826AbZKBUgz (ORCPT ); Mon, 2 Nov 2009 15:36:55 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1756790AbZKBUgy (ORCPT ); Mon, 2 Nov 2009 15:36:54 -0500 Received: from gir.skynet.ie ([193.1.99.77]:56446 "EHLO gir.skynet.ie" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756779AbZKBUgx (ORCPT ); Mon, 2 Nov 2009 15:36:53 -0500 Date: Mon, 2 Nov 2009 20:36:55 +0000 From: Mel Gorman To: Frans Pop Cc: Andrew Morton , stable@kernel.org, linux-kernel@vger.kernel.org, "linux-mm@kvack.org" , Jiri Kosina , Sven Geggus , Karol Lewandowski , Tobias Oetiker , KOSAKI Motohiro , Pekka Enberg , Rik van Riel , Christoph Lameter , Stephan von Krawczynski , Kernel Testers List Subject: Re: [PATCH 3/3] vmscan: Force kswapd to take notice faster when high-order watermarks are being hit Message-ID: <20091102203654.GD22046@csn.ul.ie> References: <1256650833-15516-1-git-send-email-mel@csn.ul.ie> <20091028124756.7af44b6b.akpm@linux-foundation.org> <20091102160534.GA22046@csn.ul.ie> <200911021832.59035.elendil@planet.nl> <20091102173837.GB22046@csn.ul.ie> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-15 Content-Disposition: inline In-Reply-To: <20091102173837.GB22046@csn.ul.ie> User-Agent: Mutt/1.5.17+20080114 (2008-01-14) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 5600 Lines: 148 On Mon, Nov 02, 2009 at 05:38:38PM +0000, Mel Gorman wrote: > On Mon, Nov 02, 2009 at 06:32:54PM +0100, Frans Pop wrote: > > On Monday 02 November 2009, Mel Gorman wrote: > > > vmscan: Help debug kswapd issues by counting number of rewakeups and > > > premature sleeps > > > > > > There is a growing amount of anedotal evidence that high-order atomic > > > allocation failures have been increasing since 2.6.31-rc1. The two > > > strongest possibilities are a marked increase in the number of > > > GFP_ATOMIC allocations and alterations in timing. Debugging printk > > > patches have shown for example that kswapd is sleeping for shorter > > > intervals and going to sleep when watermarks are still not being met. > > > > > > This patch adds two kswapd counters to help identify if timing is an > > > issue. The first counter kswapd_highorder_rewakeup counts the number of > > > times that kswapd stops reclaiming at one order and restarts at a higher > > > order. The second counter kswapd_slept_prematurely counts the number of > > > times kswapd went to sleep when the high watermark was not met. > > > > What testing would you like done with this patch? > > > > Same reproduction as before except post what the contents of > /proc/vmstat were after the problem was triggered. > In the event there is a positive count for kswapd_slept_prematurely after the error is produced, can you also check if the following patch makes a difference and what the contents of vmstat are please? It alters how kswapd behaves and when it goes to sleep. Thanks ==== CUT HERE ==== vmscan: Have kswapd sleep for a short interval and double check it should be asleep After kswapd balances all zones in a pgdat, it goes to sleep. In the event of no IO congestion, kswapd can go to sleep very shortly after the high watermark was reached. If there are a constant stream of allocations from parallel processes, it can mean that kswapd went to sleep too quickly and the high watermark is not being maintained for sufficient length time. This patch makes kswapd go to sleep as a two-stage process. It first tries to sleep for HZ/10. If it is woken up by another process or the high watermark is no longer met, it's considered a premature sleep and kswapd continues work. Otherwise it goes fully to sleep. This adds more counters to distinguish between fast and slow breaches of watermarks. A "fast" premature sleep is one where the low watermark was hit in a very short time after kswapd going to sleep. A "slow" premature sleep indicates that the high watermark was breached after a very short interval. Signed-off-by: Mel Gorman --- include/linux/vmstat.h | 3 ++- mm/vmscan.c | 31 +++++++++++++++++++++++++++---- mm/vmstat.c | 3 ++- 3 files changed, 31 insertions(+), 6 deletions(-) diff --git a/include/linux/vmstat.h b/include/linux/vmstat.h index 2e0d18d..f344878 100644 --- a/include/linux/vmstat.h +++ b/include/linux/vmstat.h @@ -40,7 +40,8 @@ enum vm_event_item { PGPGIN, PGPGOUT, PSWPIN, PSWPOUT, PGSCAN_ZONE_RECLAIM_FAILED, #endif PGINODESTEAL, SLABS_SCANNED, KSWAPD_STEAL, KSWAPD_INODESTEAL, - KSWAPD_HIGHORDER_REWAKEUP, KSWAPD_PREMATURE_SLEEP, + KSWAPD_HIGHORDER_REWAKEUP, + KSWAPD_PREMATURE_FAST, KSWAPD_PREMATURE_SLOW, PAGEOUTRUN, ALLOCSTALL, PGROTATED, #ifdef CONFIG_HUGETLB_PAGE HTLB_BUDDY_PGALLOC, HTLB_BUDDY_PGALLOC_FAIL, diff --git a/mm/vmscan.c b/mm/vmscan.c index 11a69a8..70aeb05 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -1905,10 +1905,14 @@ unsigned long try_to_free_mem_cgroup_pages(struct mem_cgroup *mem_cont, #endif /* is kswapd sleeping prematurely? */ -static int sleeping_prematurely(int order) +static int sleeping_prematurely(int order, long remaining) { struct zone *zone; + /* If a direct reclaimer woke kswapd within HZ/10, it's premature */ + if (remaining) + return 1; + /* If after HZ/10, a zone is below the high mark, it's premature */ for_each_populated_zone(zone) if (!zone_watermark_ok(zone, order, high_wmark_pages(zone), @@ -2209,9 +2213,28 @@ static int kswapd(void *p) order = new_order; } else { if (!freezing(current)) { - if (sleeping_prematurely(order)) - count_vm_event(KSWAPD_PREMATURE_SLEEP); - schedule(); + long remaining = 0; + + /* Try to sleep for a short interval */ + if (!sleeping_prematurely(order, remaining)) { + remaining = schedule_timeout(HZ/10); + finish_wait(&pgdat->kswapd_wait, &wait); + prepare_to_wait(&pgdat->kswapd_wait, &wait, TASK_INTERRUPTIBLE); + } + + /* + * After a short sleep, check if it was a + * premature sleep. If not, then go fully + * to sleep until explicitly woken up + */ + if (!sleeping_prematurely(order, remaining)) + schedule(); + else { + if (remaining) + count_vm_event(KSWAPD_PREMATURE_FAST); + else + count_vm_event(KSWAPD_PREMATURE_SLOW); + } } order = pgdat->kswapd_max_order; diff --git a/mm/vmstat.c b/mm/vmstat.c index fa881c5..47a6914 100644 --- a/mm/vmstat.c +++ b/mm/vmstat.c @@ -684,7 +684,8 @@ static const char * const vmstat_text[] = { "kswapd_steal", "kswapd_inodesteal", "kswapd_highorder_rewakeup", - "kswapd_slept_prematurely", + "kswapd_slept_prematurely_fast", + "kswapd_slept_prematurely_slow", "pageoutrun", "allocstall", -- 1.6.3.3 -- 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/