linux-kernel - Re: [RFC/T/D][PATCH 2/2] Linux/Guest cooperative unmapped page cache control

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Message-ID: <4C15E3C8.20407@redhat.com>
Date:	Mon, 14 Jun 2010 11:09:44 +0300
From:	Avi Kivity <avi@...hat.com>
To:	balbir@...ux.vnet.ibm.com
CC:	Dave Hansen <dave@...ux.vnet.ibm.com>, kvm <kvm@...r.kernel.org>,
	linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC/T/D][PATCH 2/2] Linux/Guest cooperative unmapped page cache
 control

On 06/11/2010 07:56 AM, Balbir Singh wrote:
>
>> Just to be clear, let's say we have a mapped page (say of /sbin/init)
>> that's been unreferenced since _just_ after the system booted.  We also
>> have an unmapped page cache page of a file often used at runtime, say
>> one from /etc/resolv.conf or /etc/passwd.
>>
>> Which page will be preferred for eviction with this patch set?
>>
>>      
> In this case the order is as follows
>
> 1. First we pick free pages if any
> 2. If we don't have free pages, we go after unmapped page cache and
> slab cache
> 3. If that fails as well, we go after regularly memory
>
> In the scenario that you describe, we'll not be able to easily free up
> the frequently referenced page from /etc/*. The code will move on to
> step 3 and do its regular reclaim.
>    

Still it seems to me you are subverting the normal order of reclaim.  I 
don't see why an unmapped page cache or slab cache item should be 
evicted before a mapped page.  Certainly the cost of rebuilding a dentry 
compared to the gain from evicting it, is much higher than that of 
reestablishing a mapped page.

-- 
error compiling committee.c: too many arguments to function

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