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Message-ID: <4B9E810E.9010706@codemonkey.ws>
Date: Mon, 15 Mar 2010 13:48:46 -0500
From: Anthony Liguori <anthony@codemonkey.ws>
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To: Avi Kivity <avi@redhat.com>
CC: balbir@linux.vnet.ibm.com, KVM development list <kvm@vger.kernel.org>,
       Rik van Riel <riel@surriel.com>,
       KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>,
       "linux-mm@kvack.org" <linux-mm@kvack.org>,
       "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH][RF C/T/D] Unmapped page cache control - via boot parameter
References: <20100315072214.GA18054@balbir.in.ibm.com> <4B9DE635.8030208@redhat.com> <20100315080726.GB18054@balbir.in.ibm.com> <4B9DEF81.6020802@redhat.com> <20100315091720.GC18054@balbir.in.ibm.com> <4B9DFD9C.8030608@redhat.com>
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On 03/15/2010 04:27 AM, Avi Kivity wrote:
>
> That's only beneficial if the cache is shared.  Otherwise, you could 
> use the balloon to evict cache when memory is tight.
>
> Shared cache is mostly a desktop thing where users run similar 
> workloads.  For servers, it's much less likely.  So a modified-guest 
> doesn't help a lot here.

Not really.  In many cloud environments, there's a set of common images 
that are instantiated on each node.  Usually this is because you're 
running a horizontally scalable application or because you're supporting 
an ephemeral storage model.

In fact, with ephemeral storage, you typically want to use 
cache=writeback since you aren't providing data guarantees across 
shutdown/failure.

Regards,

Anthony Liguori