linux-kernel - Re: [PATCH 4/5] add isolate pages vmstat

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Date:	Tue, 7 Jul 2009 19:32:41 -0400 (EDT)
From:	Christoph Lameter <cl@...ux-foundation.org>
To:	Rik van Riel <riel@...hat.com>
cc:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Minchan Kim <minchan.kim@...il.com>,
	Wu Fengguang <fengguang.wu@...el.com>,
	LKML <linux-kernel@...r.kernel.org>,
	linux-mm <linux-mm@...ck.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	David Rientjes <rientjes@...gle.com>
Subject: Re: [PATCH 4/5] add isolate pages vmstat

On Tue, 7 Jul 2009, Rik van Riel wrote:

> Christoph Lameter wrote:
> > On Tue, 7 Jul 2009, KOSAKI Motohiro wrote:
> >
> > > +++ b/include/linux/mmzone.h
> > > @@ -100,6 +100,8 @@ enum zone_stat_item {
> > >  	NR_BOUNCE,
> > >  	NR_VMSCAN_WRITE,
> > >  	NR_WRITEBACK_TEMP,	/* Writeback using temporary buffers */
> > > +	NR_ISOLATED_ANON,	/* Temporary isolated pages from anon lru */
> > > +	NR_ISOLATED_FILE,	/* Temporary isolated pages from file lru */
> >
> > LRU counters are rarer in use then the counters used for dirty pages etc.
> >
> > Could you move the counters for reclaim into a separate cacheline?
>
> I don't get the point of that - these counters are
> per-cpu anyway, so why would they need to be in a
> separate cacheline?

Because there are so many counters now that they spread multiple
cachelines. PCP data is very performance sensitive. Putting them in a
separate cacheline so that the most important counters are in the
first one will reduce the cache footprint of many core VM functions.
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