Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758464AbZFIHsq (ORCPT ); Tue, 9 Jun 2009 03:48:46 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1757538AbZFIHsc (ORCPT ); Tue, 9 Jun 2009 03:48:32 -0400 Received: from fgwmail7.fujitsu.co.jp ([192.51.44.37]:56112 "EHLO fgwmail7.fujitsu.co.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1758100AbZFIHsa (ORCPT ); Tue, 9 Jun 2009 03:48:30 -0400 From: KOSAKI Motohiro To: Mel Gorman Subject: Re: [PATCH 1/3] Reintroduce zone_reclaim_interval for when zone_reclaim() scans and fails to avoid CPU spinning at 100% on NUMA Cc: kosaki.motohiro@jp.fujitsu.com, Rik van Riel , Christoph Lameter , yanmin.zhang@intel.com, Wu Fengguang , linuxram@us.ibm.com, linux-mm , LKML In-Reply-To: <1244466090-10711-2-git-send-email-mel@csn.ul.ie> References: <1244466090-10711-1-git-send-email-mel@csn.ul.ie> <1244466090-10711-2-git-send-email-mel@csn.ul.ie> Message-Id: <20090609143211.DD64.A69D9226@jp.fujitsu.com> MIME-Version: 1.0 Content-Type: text/plain; charset="US-ASCII" Content-Transfer-Encoding: 7bit X-Mailer: Becky! ver. 2.50.07 [ja] Date: Tue, 9 Jun 2009 16:48:28 +0900 (JST) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 7436 Lines: 191 Hi > On NUMA machines, the administrator can configure zone_reclaim_mode that is a > more targetted form of direct reclaim. On machines with large NUMA distances, > zone_reclaim_mode defaults to 1 meaning that clean unmapped pages will be > reclaimed if the zone watermarks are not being met. The problem is that > zone_reclaim() can be in a situation where it scans excessively without > making progress. > > One such situation is where a large tmpfs mount is occupying a large > percentage of memory overall. The pages do not get cleaned or reclaimed by > zone_reclaim(), but the lists are uselessly scanned frequencly making the > CPU spin at 100%. The scanning occurs because zone_reclaim() cannot tell > in advance the scan is pointless because the counters do not distinguish > between pagecache pages backed by disk and by RAM. The observation in > the field is that malloc() stalls for a long time (minutes in some cases) > when this situation occurs. > > Accounting for ram-backed file pages was considered but not implemented on > the grounds it would be introducing new branches and expensive checks into > the page cache add/remove patches and increase the number of statistics > needed in the zone. As zone_reclaim() failing is currently considered a > corner case, this seemed like overkill. Note, if there are a large number > of reports about CPU spinning at 100% on NUMA that is fixed by disabling > zone_reclaim, then this assumption is false and zone_reclaim() scanning > and failing is not a corner case but a common occurance > > This patch reintroduces zone_reclaim_interval which was removed by commit > 34aa1330f9b3c5783d269851d467326525207422 [zoned vm counters: zone_reclaim: > remove /proc/sys/vm/zone_reclaim_interval] because the zone counters were > considered sufficient to determine in advance if the scan would succeed. > As unsuccessful scans can still occur, zone_reclaim_interval is still > required. > > Signed-off-by: Mel Gorman --- > Documentation/sysctl/vm.txt | 13 +++++++++++++ > include/linux/mmzone.h | 9 +++++++++ > include/linux/swap.h | 1 + > kernel/sysctl.c | 9 +++++++++ > mm/vmscan.c | 22 ++++++++++++++++++++++ > 5 files changed, 54 insertions(+), 0 deletions(-) > > diff --git a/Documentation/sysctl/vm.txt b/Documentation/sysctl/vm.txt > index c302ddf..f9b8db5 100644 > --- a/Documentation/sysctl/vm.txt > +++ b/Documentation/sysctl/vm.txt > @@ -52,6 +52,7 @@ Currently, these files are in /proc/sys/vm: > - swappiness > - vfs_cache_pressure > - zone_reclaim_mode > +- zone_reclaim_interval > > > ============================================================== > @@ -620,4 +621,16 @@ Allowing regular swap effectively restricts allocations to the local > node unless explicitly overridden by memory policies or cpuset > configurations. > > +================================================================ > + > +zone_reclaim_interval: > + > +The time allowed for off node allocations after zone reclaim > +has failed to reclaim enough pages to allow a local allocation. > + > +Time is set in seconds and set by default to 30 seconds. > + > +Reduce the interval if undesired off node allocations occur. However, too > +frequent scans will have a negative impact on off-node allocation performance. > + > ============ End of Document ================================= > diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h > index a47c879..f1f0fb2 100644 > --- a/include/linux/mmzone.h > +++ b/include/linux/mmzone.h > @@ -337,6 +337,15 @@ struct zone { > atomic_long_t vm_stat[NR_VM_ZONE_STAT_ITEMS]; > > /* > + * timestamp (in jiffies) of the last zone_reclaim that scanned > + * but failed to free enough pages. This is used to avoid repeated > + * scans when zone_reclaim() is unable to detect in advance that > + * the scanning is useless. This can happen for example if a zone > + * has large numbers of clean unmapped file pages on tmpfs > + */ > + unsigned long zone_reclaim_failure; > + > + /* > * prev_priority holds the scanning priority for this zone. It is > * defined as the scanning priority at which we achieved our reclaim > * target at the previous try_to_free_pages() or balance_pgdat() > diff --git a/include/linux/swap.h b/include/linux/swap.h > index d476aad..6a71368 100644 > --- a/include/linux/swap.h > +++ b/include/linux/swap.h > @@ -224,6 +224,7 @@ extern long vm_total_pages; > > #ifdef CONFIG_NUMA > extern int zone_reclaim_mode; > +extern int zone_reclaim_interval; > extern int sysctl_min_unmapped_ratio; > extern int sysctl_min_slab_ratio; > extern int zone_reclaim(struct zone *, gfp_t, unsigned int); > diff --git a/kernel/sysctl.c b/kernel/sysctl.c > index b2970d5..cc0623c 100644 > --- a/kernel/sysctl.c > +++ b/kernel/sysctl.c > @@ -1192,6 +1192,15 @@ static struct ctl_table vm_table[] = { > .extra1 = &zero, > }, > { > + .ctl_name = CTL_UNNUMBERED, > + .procname = "zone_reclaim_interval", > + .data = &zone_reclaim_interval, > + .maxlen = sizeof(zone_reclaim_interval), > + .mode = 0644, > + .proc_handler = &proc_dointvec_jiffies, > + .strategy = &sysctl_jiffies, > + }, hmmm, I think nobody can know proper interval settings on his own systems. I agree with Wu. It can be hidden. > + { > .ctl_name = VM_MIN_UNMAPPED, > .procname = "min_unmapped_ratio", > .data = &sysctl_min_unmapped_ratio, > diff --git a/mm/vmscan.c b/mm/vmscan.c > index d254306..ba211c1 100644 > --- a/mm/vmscan.c > +++ b/mm/vmscan.c > @@ -2272,6 +2272,13 @@ int zone_reclaim_mode __read_mostly; > #define RECLAIM_SWAP (1<<2) /* Swap pages out during reclaim */ > > /* > + * Minimum time between zone_reclaim() scans that failed. Ordinarily, a > + * scan will not fail because it will be determined in advance if it can > + * succeeed but this does not always work. See mmzone.h > + */ > +int zone_reclaim_interval __read_mostly = 30*HZ; > + > +/* > * Priority for ZONE_RECLAIM. This determines the fraction of pages > * of a node considered for each zone_reclaim. 4 scans 1/16th of > * a zone. > @@ -2390,6 +2397,11 @@ int zone_reclaim(struct zone *zone, gfp_t gfp_mask, unsigned int order) > <= zone->min_slab_pages) > return 0; > > + /* Do not attempt a scan if scanning failed recently */ > + if (time_before(jiffies, > + zone->zone_reclaim_failure + zone_reclaim_interval)) > + return 0; > + > if (zone_is_all_unreclaimable(zone)) > return 0; > > @@ -2414,6 +2426,16 @@ int zone_reclaim(struct zone *zone, gfp_t gfp_mask, unsigned int order) > ret = __zone_reclaim(zone, gfp_mask, order); > zone_clear_flag(zone, ZONE_RECLAIM_LOCKED); > > + if (!ret) { > + /* > + * We were unable to reclaim enough pages to stay on node and > + * unable to detect in advance that the scan would fail. Allow > + * off node accesses for zone_reclaim_inteval jiffies before > + * trying zone_reclaim() again > + */ > + zone->zone_reclaim_failure = jiffies; Oops, this simple assignment don't care jiffies round-trip. > + } > + > return ret; > } > #endif > -- > 1.5.6.5 > -- 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/