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 D05DA6B004D for ; Sun, 16 Aug 2009 11:32:25 -0400 (EDT) Date: Sun, 16 Aug 2009 08:34:34 -0700 From: Arjan van de Ven Subject: Re: Discard support (was Re: [PATCH] swap: send callback when swap slot is freed) Message-ID: <20090816083434.2ce69859@infradead.org> In-Reply-To: <20090816150530.2bae6d1f@lxorguk.ukuu.org.uk> References: <200908122007.43522.ngupta@vflare.org> <20090813151312.GA13559@linux.intel.com> <20090813162621.GB1915@phenom2.trippelsdorf.de> <87f94c370908131115r680a7523w3cdbc78b9e82373c@mail.gmail.com> <3e8340490908131354q167840fcv124ec56c92bbb830@mail.gmail.com> <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> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org To: Alan Cox Cc: James Bottomley , 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, 16 Aug 2009 15:05:30 +0100 Alan Cox wrote: > On Sat, 15 Aug 2009 08:55:17 -0500 > James Bottomley wrote: > > > On Sat, 2009-08-15 at 09:22 -0400, Mark Lord wrote: > > > James Bottomley wrote: > > > > > > > > This means you have to drain the outstanding NCQ commands > > > > (stalling the device) before you can send a TRIM. If we do > > > > this for every discard, the performance impact will be pretty > > > > devastating, hence the need to coalesce. It's nothing really > > > > to do with device characteristics, it's an ATA protocol problem. > > > .. > > > > > > I don't think that's really much of an issue -- we already have > > > to do that for cache-flushes whenever barriers are enabled. Yes > > > it costs, but not too much. > > > > That's not really what the enterprise is saying about flush > > barriers. True, not all the performance problems are NCQ queue > > drain, but for a steady workload they are significant. > > Flush barriers are nightmare for more than enterprise. You drive > basically goes for a hike for a bit which trashes interactivity as > well. If the device can't do trim and the like without a drain I > don't see much point doing it at all, except maybe to wait for idle > devices and run a filesystem managed background 'strimmer' thread to > just weed out now idle blocks that have stayed idle - eg by adding an > inode of all the deleted untrimmed blocks and giving it an irregular > empty ? > trim is mostly for ssd's though, and those tend to not have the "goes for a hike" behavior as much...... I wonder if it's worse to batch stuff up, because then the trim itself gets bigger and might take longer..... -- Arjan van de Ven Intel Open Source Technology Centre For development, discussion and tips for power savings, visit http://www.lesswatts.org -- 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