linux-kernel - Re: [PATCH 3/3] Provide control over unmapped pages

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Message-Id: <20101202115036.1a4a42b5.kamezawa.hiroyu@jp.fujitsu.com>
Date:	Thu, 2 Dec 2010 11:50:36 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
Cc:	Christoph Lameter <cl@...ux.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Balbir Singh <balbir@...ux.vnet.ibm.com>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, kvm <kvm@...r.kernel.org>
Subject: Re: [PATCH 3/3] Provide control over unmapped pages

On Thu,  2 Dec 2010 10:22:16 +0900 (JST)
KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com> wrote:

> > On Tue, 30 Nov 2010, Andrew Morton wrote:
> > 
> > > > +#define UNMAPPED_PAGE_RATIO 16
> > >
> > > Well.  Giving 16 a name didn't really clarify anything.  Attentive
> > > readers will want to know what this does, why 16 was chosen and what
> > > the effects of changing it will be.
> > 
> > The meaning is analoguous to the other zone reclaim ratio. But yes it
> > should be justified and defined.
> > 
> > > > Reviewed-by: Christoph Lameter <cl@...ux.com>
> > >
> > > So you're OK with shoving all this flotsam into 100,000,000 cellphones?
> > > This was a pretty outrageous patchset!
> > 
> > This is a feature that has been requested over and over for years. Using
> > /proc/vm/drop_caches for fixing situations where one simply has too many
> > page cache pages is not so much fun in the long run.
> 
> I'm not against page cache limitation feature at all. But, this is
> too ugly and too destructive fast path. I hope this patch reduce negative
> impact more.
> 

And I think min_mapped_unmapped_pages is ugly. It should be
"unmapped_pagecache_limit" or some because it's for limitation feature.

Thanks,
-Kame

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