From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail144.messagelabs.com (mail144.messagelabs.com [216.82.254.51]) by kanga.kvack.org (Postfix) with ESMTP id 49B006B004D for ; Sun, 16 Aug 2009 13:00:10 -0400 (EDT) Date: Sun, 16 Aug 2009 12:59:43 -0400 From: Christoph Hellwig Subject: Re: Discard support (was Re: [PATCH] swap: send callback when swap slot is freed) Message-ID: <20090816165943.GA26983@infradead.org> References: <4A85E0DC.9040101@rtr.ca> <20090814234539.GE27148@parisc-linux.org> <1250341176.4159.2.camel@mulgrave.site> <4A86B69C.7090001@rtr.ca> <1250344518.4159.4.camel@mulgrave.site> <20090816150530.2bae6d1f@lxorguk.ukuu.org.uk> <20090816083434.2ce69859@infradead.org> <1250437927.3856.119.camel@mulgrave.site> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1250437927.3856.119.camel@mulgrave.site> Sender: owner-linux-mm@kvack.org To: James Bottomley Cc: Arjan van de Ven , Alan Cox , Mark Lord , Chris Worley , Matthew Wilcox , Bryan Donlan , david@lang.hm, Greg Freemyer , Markus Trippelsdorf , Matthew Wilcox , Hugh Dickins , Nitin Gupta , Ingo Molnar , Peter Zijlstra , linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-scsi@vger.kernel.org, linux-ide@vger.kernel.org, Linux RAID List-ID: On Sun, Aug 16, 2009 at 10:52:07AM -0500, James Bottomley wrote: > However, the enterprise has been doing UNMAP for a while, so we can draw > inferences from them since the SSD FTL will operate similarly. For > them, UNMAP is the same cost in terms of time regardless of the number > of extents. The reason is that it's moving the blocks from the global > in use list to the global free list. Part of the problem is that this > involves locking and quiescing, so UNMAP ends up being quite expensive > to the array but constant in terms of cost (hence they want as few > unmaps for as many sectors as possible). How are they doing the unmaps? Using something similar to Mark's wiper script and using SG_IO? Because right now we do not actually implement UNMAP support in the kernel. I'd really love to test the XFS batched discard support with a real UNMAP implementation. -- 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