Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756769AbZKMSRo (ORCPT ); Fri, 13 Nov 2009 13:17:44 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1756634AbZKMSRj (ORCPT ); Fri, 13 Nov 2009 13:17:39 -0500 Received: from gir.skynet.ie ([193.1.99.77]:34017 "EHLO gir.skynet.ie" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755170AbZKMSRi (ORCPT ); Fri, 13 Nov 2009 13:17:38 -0500 Date: Fri, 13 Nov 2009 18:17:40 +0000 From: Mel Gorman To: KOSAKI Motohiro Cc: Andrew Morton , Frans Pop , Jiri Kosina , Sven Geggus , Karol Lewandowski , Tobias Oetiker , linux-kernel@vger.kernel.org, "linux-mm@kvack.org" , Pekka Enberg , Rik van Riel , Christoph Lameter , Stephan von Krawczynski , "Rafael J. Wysocki" , Kernel Testers List Subject: Re: [PATCH 4/5] vmscan: Have kswapd sleep for a short interval and double check it should be asleep Message-ID: <20091113181740.GN29804@csn.ul.ie> References: <20091113142558.33B6.A69D9226@jp.fujitsu.com> <20091113141303.GI29804@csn.ul.ie> <20091114023901.3DA8.A69D9226@jp.fujitsu.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-15 Content-Disposition: inline In-Reply-To: <20091114023901.3DA8.A69D9226@jp.fujitsu.com> 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: 6693 Lines: 166 On Sat, Nov 14, 2009 at 03:00:57AM +0900, KOSAKI Motohiro wrote: > > On Fri, Nov 13, 2009 at 07:43:09PM +0900, KOSAKI Motohiro wrote: > > > > 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 > > > > > > Why do you submit this patch to mainline? this is debugging patch > > > no more and no less. > > > > > > > Do you mean the stats part? The stats are included until such time as the page > > allocator failure reports stop or are significantly reduced. In the event a > > report is received, the value of the counters help determine if kswapd was > > struggling or not. They should be removed once this mess is ironed out. > > > > If there is a preference, I can split out the stats part and send it to > > people with page allocator failure reports for retesting. > > I'm sorry my last mail didn't have enough explanation. > This stats help to solve this issue. I agreed. but after solving this issue, > I don't imagine administrator how to use this stats. if KSWAPD_PREMATURE_FAST or > KSWAPD_PREMATURE_SLOW significantly increased, what should admin do? One possible workaround would be to raise min_free_kbytes while a fix is being worked on. > Or, Can LKML folk make any advise to admin? > Work with them to fix the bug :/ > if kernel doesn't have any bug, kswapd wakeup rate is not so worth information imho. > following your additional code itself looks good to me. but... > > > > ==== CUT HERE ==== > > vmscan: Have kswapd sleep for a short interval and double check it should be asleep fix 1 > > > > This patch is a fix and a claritifacation to the patch "vmscan: Have > > kswapd sleep for a short interval and double check it should be asleep". > > The fix is for kswapd to only check zones in the node it is responsible > > for. The clarification is to rename two counters to better explain what is > > being counted. > > > > Signed-off-by: Mel Gorman > > --- > > include/linux/vmstat.h | 2 +- > > mm/vmscan.c | 20 +++++++++++++------- > > mm/vmstat.c | 4 ++-- > > 3 files changed, 16 insertions(+), 10 deletions(-) > > > > diff --git a/include/linux/vmstat.h b/include/linux/vmstat.h > > index 7d66695..0591a48 100644 > > --- a/include/linux/vmstat.h > > +++ b/include/linux/vmstat.h > > @@ -40,7 +40,7 @@ enum vm_event_item { PGPGIN, PGPGOUT, PSWPIN, PSWPOUT, > > PGSCAN_ZONE_RECLAIM_FAILED, > > #endif > > PGINODESTEAL, SLABS_SCANNED, KSWAPD_STEAL, KSWAPD_INODESTEAL, > > - KSWAPD_PREMATURE_FAST, KSWAPD_PREMATURE_SLOW, > > + KSWAPD_LOW_WMARK_HIT_QUICKLY, KSWAPD_HIGH_WMARK_HIT_QUICKLY, > > KSWAPD_NO_CONGESTION_WAIT, > > PAGEOUTRUN, ALLOCSTALL, PGROTATED, > > #ifdef CONFIG_HUGETLB_PAGE > > diff --git a/mm/vmscan.c b/mm/vmscan.c > > index 70967e1..5557555 100644 > > --- a/mm/vmscan.c > > +++ b/mm/vmscan.c > > @@ -1905,19 +1905,25 @@ unsigned long try_to_free_mem_cgroup_pages(struct mem_cgroup *mem_cont, > > #endif > > > > /* is kswapd sleeping prematurely? */ > > -static int sleeping_prematurely(int order, long remaining) > > +static int sleeping_prematurely(pg_data_t *pgdat, int order, long remaining) > > { > > - struct zone *zone; > > + int i; > > > > /* 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) > > + for (i = 0; i < pgdat->nr_zones; i++) { > > + struct zone *zone = pgdat->node_zones + i; > > + > > + if (!populated_zone(zone)) > > + continue; > > + > > if (!zone_watermark_ok(zone, order, high_wmark_pages(zone), > > 0, 0)) > > return 1; > > + } > > > > return 0; > > } > > @@ -2221,7 +2227,7 @@ static int kswapd(void *p) > > long remaining = 0; > > > > /* Try to sleep for a short interval */ > > - if (!sleeping_prematurely(order, remaining)) { > > + if (!sleeping_prematurely(pgdat, order, remaining)) { > > remaining = schedule_timeout(HZ/10); > > finish_wait(&pgdat->kswapd_wait, &wait); > > prepare_to_wait(&pgdat->kswapd_wait, &wait, TASK_INTERRUPTIBLE); > > @@ -2232,13 +2238,13 @@ static int kswapd(void *p) > > * premature sleep. If not, then go fully > > * to sleep until explicitly woken up > > */ > > - if (!sleeping_prematurely(order, remaining)) > > + if (!sleeping_prematurely(pgdat, order, remaining)) > > schedule(); > > else { > > if (remaining) > > - count_vm_event(KSWAPD_PREMATURE_FAST); > > + count_vm_event(KSWAPD_LOW_WMARK_HIT_QUICKLY); > > else > > - count_vm_event(KSWAPD_PREMATURE_SLOW); > > + count_vm_event(KSWAPD_HIGH_WMARK_HIT_QUICKLY); > > } > > } > > > > diff --git a/mm/vmstat.c b/mm/vmstat.c > > index bc09547..6cc8dc6 100644 > > --- a/mm/vmstat.c > > +++ b/mm/vmstat.c > > @@ -683,8 +683,8 @@ static const char * const vmstat_text[] = { > > "slabs_scanned", > > "kswapd_steal", > > "kswapd_inodesteal", > > - "kswapd_slept_prematurely_fast", > > - "kswapd_slept_prematurely_slow", > > + "kswapd_low_wmark_hit_quickly", > > + "kswapd_high_wmark_hit_quickly", > > "kswapd_no_congestion_wait", > > "pageoutrun", > > "allocstall", > > > -- Mel Gorman Part-time Phd Student Linux Technology Center University of Limerick IBM Dublin Software Lab -- 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/