linux-kernel - Re: [PATCH 1/3] Reintroduce zone_reclaim_interval for when zone_reclaim() scans and fails to avoid CPU spinning at 100% on NUMA

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Date:	Wed, 10 Jun 2009 15:44:03 +0900 (JST)
From:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	kosaki.motohiro@...fujitsu.com, Mel Gorman <mel@....ul.ie>,
	Christoph Lameter <cl@...ux-foundation.org>,
	Rik van Riel <riel@...hat.com>, yanmin.zhang@...el.com,
	Wu Fengguang <fengguang.wu@...el.com>, linuxram@...ibm.com,
	linux-mm <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/3] Reintroduce zone_reclaim_interval for when zone_reclaim() scans and fails to avoid CPU spinning at 100% on NUMA

Hi

> On Mon, 8 Jun 2009 16:11:51 +0100 Mel Gorman <mel@....ul.ie> wrote:
> 
> > On Mon, Jun 08, 2009 at 10:55:55AM -0400, Christoph Lameter wrote:
> > > On Mon, 8 Jun 2009, Mel Gorman wrote:
> > > 
> > > > > The tmpfs pages are unreclaimable and therefore should not be on the anon
> > > > > lru.
> > > > >
> > > >
> > > > tmpfs pages can be swap-backed so can be reclaimable. Regardless of what
> > > > list they are on, we still need to know how many of them there are if
> > > > this patch is to be avoided.
> > > 
> > > If they are reclaimable then why does it matter? They can be pushed out if
> > > you configure zone reclaim to be that aggressive.
> > > 
> > 
> > Because they are reclaimable by kswapd or normal direct reclaim but *not*
> > reclaimable by zone_reclaim() if the zone_reclaim_mode is not configured
> > appropriately.
> 
> Ah.  (zone_reclaim_mode & RECLAIM_SWAP) == 0.  That was important info.
> 
> Couldn't the lack of RECLAIM_WRITE cause a similar problem?

Old kernel can makes easily. but currenly we have proper dirty page limit.
Thus all pages can't become dirty and zone-reclaim can found cleaner page.

In the other hand, plenty tmpfs pages can be mede easily.



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