From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail203.messagelabs.com (mail203.messagelabs.com [216.82.254.243]) by kanga.kvack.org (Postfix) with SMTP id 8CADB6B004D for ; Mon, 17 Aug 2009 09:56:20 -0400 (EDT) Subject: Re: Discard support (was Re: [PATCH] swap: send callback when swap slot is freed) From: James Bottomley In-Reply-To: <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> <20090816165943.GA26983@infradead.org> Content-Type: text/plain Date: Mon, 17 Aug 2009 08:56:12 -0500 Message-Id: <1250517372.3844.3.camel@mulgrave.site> Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org To: Christoph Hellwig 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, 2009-08-16 at 12:59 -0400, Christoph Hellwig wrote: > 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. You mean how is the array vendor testing their implementation? Using SG_IO ... without any filesystem, I believe. The testing was initially done to see if the initial maximal discard proposal from LSF09 was a viable approach (which it wasn't given the time taken to UNMAP). James -- 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