From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail191.messagelabs.com (mail191.messagelabs.com [216.82.242.19]) by kanga.kvack.org (Postfix) with ESMTP id 856B36B0204 for ; Wed, 17 Mar 2010 12:52:37 -0400 (EDT) Date: Wed, 17 Mar 2010 17:52:29 +0100 From: Christoph Hellwig Subject: Re: [PATCH][RF C/T/D] Unmapped page cache control - via boot parameter Message-ID: <20100317165229.GA29548@lst.de> References: <20100315072214.GA18054@balbir.in.ibm.com> <4B9DE635.8030208@redhat.com> <20100315080726.GB18054@balbir.in.ibm.com> <4B9DEF81.6020802@redhat.com> <20100315202353.GJ3840@arachsys.com> <4B9F4CBD.3020805@redhat.com> <20100317152452.GZ31148@arachsys.com> <4BA101C5.9040406@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <4BA101C5.9040406@redhat.com> Sender: owner-linux-mm@kvack.org To: Avi Kivity Cc: Chris Webb , balbir@linux.vnet.ibm.com, KVM development list , Rik van Riel , KAMEZAWA Hiroyuki , "linux-mm@kvack.org" , "linux-kernel@vger.kernel.org" , Christoph Hellwig , Kevin Wolf List-ID: On Wed, Mar 17, 2010 at 06:22:29PM +0200, Avi Kivity wrote: > They should be reorderable. Otherwise host filesystems on several > volumes would suffer the same problems. They are reordable, just not as extremly as the the page cache. Remember that the request queue really is just a relatively small queue of outstanding I/O, and that is absolutely intentional. Large scale _caching_ is done by the VM in the pagecache, with all the usual aging, pressure, etc algorithms applied to it. The block devices have a relatively small fixed size request queue associated with it to facilitate request merging and limited reordering and having fully set up I/O requests for the device. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org