From mboxrd@z Thu Jan 1 00:00:00 1970 From: Matthew Wilcox Subject: Re: thin provisioned LUN support & file system allocation policy Date: Fri, 7 Nov 2008 07:55:50 -0700 Message-ID: <20081107145549.GG15439@parisc-linux.org> References: <4913028B.6010405@redhat.com> <1225984628.4703.80.camel@localhost.localdomain> <20081107120534.GO21867@kernel.dk> <49143142.4010809@redhat.com> <20081107121934.GP21867@kernel.dk> <49145029.4040900@redhat.com> <20081107144311.GE9543@mit.edu> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Received: from palinux.external.hp.com ([192.25.206.14]:44086 "EHLO mail.parisc-linux.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751864AbYKGOzv (ORCPT ); Fri, 7 Nov 2008 09:55:51 -0500 Content-Disposition: inline In-Reply-To: <20081107144311.GE9543@mit.edu> Sender: linux-scsi-owner@vger.kernel.org List-Id: linux-scsi@vger.kernel.org To: Theodore Tso , Ric Wheeler , Jens Axboe , Chris Mason , Dave Chinner , David On Fri, Nov 07, 2008 at 09:43:11AM -0500, Theodore Tso wrote: > The one thing we might need for SSD-friendly allocation policies is to > tell the allocators to not try so hard to make sure allocations are > contiguous, but there are other reasons why you want contiguous > extents anyway (such as reducing the size of your extent tree and > reducing the number of block allocation data structures that need to > be updated). And, I think to some extent SSD's do care to some level > about contiguous extents, from the point of view of reducing scatter > gather operations if nothing else, right? It's not so much s-g operations as it is that you can only have 32 commands outstanding with the drive at any given time. Each read/write command can specify only one extent. So if you can ask for one 256k extent rather than have to ask for a 4k extent 64 times, you're going to get your data faster. -- Matthew Wilcox Intel Open Source Technology Centre "Bill, look, we understand that you're interested in selling us this operating system, but compare it to ours. We can't possibly take such a retrograde step."