From: Mel Gorman <mel@csn.ul.ie>
To: Christoph Lameter <cl@linux.com>
Cc: David Rientjes <rientjes@google.com>,
Shaohua Li <shaohua.li@intel.com>,
linux-mm@kvack.org
Subject: Re: zone state overhead
Date: Wed, 29 Sep 2010 15:41:59 +0100 [thread overview]
Message-ID: <20100929144159.GC14204@csn.ul.ie> (raw)
In-Reply-To: <alpine.DEB.2.00.1009290930360.1538@router.home>
On Wed, Sep 29, 2010 at 09:34:09AM -0500, Christoph Lameter wrote:
> On Wed, 29 Sep 2010, Mel Gorman wrote:
>
> > > Updating the threshold also is expensive.
> >
> > Even if it's moved to a read-mostly part of the zone such as after
> > lowmem_reserve?
>
> The threshold is stored in the hot part of the per cpu page structure.
>
And the consequences of moving it? In terms of moving, it would probably
work out better to move percpu_drift_mark after the lowmem_reserve and
put the threshold after it so they're at least similarly hot across
CPUs.
> > > I thought more along the lines
> > > of reducing the threshold for good if the VM runs into reclaim trouble
> > > because of too high fuzziness in the counters.
> > >
> >
> > That would be unfortunate as it would only take trouble to happen once
> > for performance to be impaired for the remaining uptime of the machine.
>
> Reclaim also impairs performance and inaccurate counters may cause
> unnecessary reclaim.
Ah, it's limited to be fair. You might end up reclaiming "maximum drift"
number of pages you didn't need to but that doesn't seem as bad.
> Ultimately this is a tradeoff. The current thresholds
> were calculated so that there will be zero impact even for very large
> configurations where all processors continual page fault. I think we have
> some leeway to go lower there. The tuning situation was a bit extreme.
>
Ok.
--
Mel Gorman
Part-time Phd Student Linux Technology Center
University of Limerick IBM Dublin Software Lab
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next prev parent reply other threads:[~2010-09-29 14:42 UTC|newest]
Thread overview: 65+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-09-28 5:08 zone state overhead Shaohua Li
2010-09-28 12:39 ` Christoph Lameter
2010-09-28 13:30 ` Mel Gorman
2010-09-28 13:40 ` Christoph Lameter
2010-09-28 13:51 ` Mel Gorman
2010-09-28 14:08 ` Christoph Lameter
2010-09-29 3:02 ` Shaohua Li
2010-09-29 4:02 ` David Rientjes
2010-09-29 4:47 ` Shaohua Li
2010-09-29 5:06 ` David Rientjes
2010-09-29 10:03 ` Mel Gorman
2010-09-29 14:12 ` Christoph Lameter
2010-09-29 14:17 ` Mel Gorman
2010-09-29 14:34 ` Christoph Lameter
2010-09-29 14:41 ` Mel Gorman [this message]
2010-09-29 14:45 ` Mel Gorman
2010-09-29 14:54 ` Christoph Lameter
2010-09-29 14:52 ` Christoph Lameter
2010-09-29 19:44 ` David Rientjes
2010-10-08 15:29 ` Mel Gorman
2010-10-09 0:58 ` Shaohua Li
2010-10-11 8:56 ` Mel Gorman
2010-10-12 1:05 ` Shaohua Li
2010-10-12 16:25 ` Mel Gorman
2010-10-13 2:41 ` Shaohua Li
2010-10-13 12:09 ` Mel Gorman
2010-10-13 3:36 ` KOSAKI Motohiro
2010-10-13 6:25 ` [RFC][PATCH 0/3] mm: reserve max drift pages at boot time instead using zone_page_state_snapshot() KOSAKI Motohiro
2010-10-13 6:27 ` [RFC][PATCH 1/3] mm, mem-hotplug: recalculate lowmem_reserve when memory hotplug occur KOSAKI Motohiro
2010-10-13 6:39 ` KAMEZAWA Hiroyuki
2010-10-13 12:59 ` Mel Gorman
2010-10-14 2:44 ` KOSAKI Motohiro
2010-10-13 6:28 ` [RFC][PATCH 2/3] mm: update pcp->stat_threshold " KOSAKI Motohiro
2010-10-13 6:40 ` KAMEZAWA Hiroyuki
2010-10-13 13:02 ` Mel Gorman
2010-10-13 6:32 ` [RFC][PATCH 3/3] mm: reserve max drift pages at boot time instead using zone_page_state_snapshot() KOSAKI Motohiro
2010-10-13 13:19 ` Mel Gorman
2010-10-14 2:39 ` KOSAKI Motohiro
2010-10-18 10:43 ` Mel Gorman
2010-10-13 7:10 ` [experimental][PATCH] mm,vmstat: per cpu stat flush too when per cpu page cache flushed KOSAKI Motohiro
2010-10-13 7:16 ` KAMEZAWA Hiroyuki
2010-10-13 13:22 ` Mel Gorman
2010-10-14 2:50 ` KOSAKI Motohiro
2010-10-15 17:31 ` Christoph Lameter
2010-10-18 9:27 ` KOSAKI Motohiro
2010-10-18 15:44 ` Christoph Lameter
2010-10-19 1:10 ` KOSAKI Motohiro
2010-10-18 11:08 ` Mel Gorman
2010-10-19 1:34 ` KOSAKI Motohiro
2010-10-19 9:06 ` Mel Gorman
2010-10-18 15:51 ` Christoph Lameter
2010-10-19 0:43 ` KOSAKI Motohiro
2010-10-13 11:24 ` zone state overhead Mel Gorman
2010-10-14 3:07 ` KOSAKI Motohiro
2010-10-18 10:39 ` Mel Gorman
2010-10-19 1:16 ` KOSAKI Motohiro
2010-10-19 9:08 ` Mel Gorman
2010-10-22 14:12 ` Mel Gorman
2010-10-22 15:23 ` Christoph Lameter
2010-10-22 18:45 ` Mel Gorman
2010-10-22 15:27 ` Christoph Lameter
2010-10-22 18:46 ` Mel Gorman
2010-10-22 20:01 ` Christoph Lameter
2010-10-25 4:46 ` KOSAKI Motohiro
2010-10-27 8:19 ` Mel Gorman
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