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Message-Id: <20090611203232.6D65.A69D9226@jp.fujitsu.com>
Date: Thu, 11 Jun 2009 20:33:00 +0900 (JST)
From: KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
To: Mel Gorman <mel@....ul.ie>
Cc: kosaki.motohiro@...fujitsu.com,
Andrew Morton <akpm@...ux-foundation.org>,
Rik van Riel <riel@...hat.com>,
Christoph Lameter <cl@...ux-foundation.org>,
Wu Fengguang <fengguang.wu@...el.com>, linuxram@...ibm.com,
linux-mm <linux-mm@...ck.org>,
LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 3/3] Count the number of times zone_reclaim() scans and fails
> 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 for example, a zone_reclaim_mode defaults to 1 meaning that clean
> unmapped pages will be reclaimed if the zone watermarks are not being met.
>
> There is a heuristic that determines if the scan is worthwhile but it is
> possible that the heuristic will fail and the CPU gets tied up scanning
> uselessly. Detecting the situation requires some guesswork and experimentation
> so this patch adds a counter "zreclaim_failed" to /proc/vmstat. If during
> high CPU utilisation this counter is increasing rapidly, then the resolution
> to the problem may be to set /proc/sys/vm/zone_reclaim_mode to 0.
>
> Signed-off-by: Mel Gorman <mel@....ul.ie>
> Reviewed-by: Rik van Riel <riel@...hat.com>
> ---
> include/linux/vmstat.h | 3 +++
> mm/vmscan.c | 3 +++
> mm/vmstat.c | 3 +++
> 3 files changed, 9 insertions(+), 0 deletions(-)
>
> diff --git a/include/linux/vmstat.h b/include/linux/vmstat.h
> index ff4696c..416f748 100644
> --- a/include/linux/vmstat.h
> +++ b/include/linux/vmstat.h
> @@ -36,6 +36,9 @@ enum vm_event_item { PGPGIN, PGPGOUT, PSWPIN, PSWPOUT,
> FOR_ALL_ZONES(PGSTEAL),
> FOR_ALL_ZONES(PGSCAN_KSWAPD),
> FOR_ALL_ZONES(PGSCAN_DIRECT),
> +#ifdef CONFIG_NUMA
> + PGSCAN_ZONERECLAIM_FAILED,
> +#endif
> PGINODESTEAL, SLABS_SCANNED, KSWAPD_STEAL, KSWAPD_INODESTEAL,
> PAGEOUTRUN, ALLOCSTALL, PGROTATED,
> #ifdef CONFIG_HUGETLB_PAGE
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index 7b8eb3f..42c1013 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -2492,6 +2492,9 @@ 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)
> + count_vm_event(PGSCAN_ZONERECLAIM_FAILED);
> +
> return ret;
> }
> #endif
> diff --git a/mm/vmstat.c b/mm/vmstat.c
> index 1e3aa81..02677d1 100644
> --- a/mm/vmstat.c
> +++ b/mm/vmstat.c
> @@ -673,6 +673,9 @@ static const char * const vmstat_text[] = {
> TEXTS_FOR_ZONES("pgscan_kswapd")
> TEXTS_FOR_ZONES("pgscan_direct")
>
> +#ifdef CONFIG_NUMA
> + "zreclaim_failed",
> +#endif
> "pginodesteal",
> "slabs_scanned",
> "kswapd_steal",
Looks good.
Reviewed-by: KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
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