From: Markus Trippelsdorf Subject: Re: [PATCH 1/2] fs: Do not dispatch FITRIM through separate super_operation Date: Thu, 18 Nov 2010 20:32:55 +0100 Message-ID: <20101118193255.GE1594@arch.trippelsdorf.de> References: <1290065809-3976-1-git-send-email-lczerner@redhat.com> <20101118130630.GJ6178@parisc-linux.org> <20101118134804.GN5618@dhcp231-156.rdu.redhat.com> <20101118141957.GK6178@parisc-linux.org> <20101118142918.GA18510@infradead.org> <1290100750.3041.72.camel@mulgrave.site> <20101118180557.GU22787@shareable.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Jeff Moyer , James Bottomley , Christoph Hellwig , Matthew Wilcox , Josef Bacik , Lukas Czerner , tytso@mit.edu, linux-ext4@vger.kernel.org, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, sandeen@redhat.com To: Jamie Lokier Return-path: Received: from smtp-out-249.synserver.de ([212.40.180.249]:1075 "HELO smtp-out-247.synserver.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with SMTP id S1754892Ab0KRTc6 (ORCPT ); Thu, 18 Nov 2010 14:32:58 -0500 Content-Disposition: inline In-Reply-To: <20101118180557.GU22787@shareable.org> Sender: linux-ext4-owner@vger.kernel.org List-ID: On 2010.11.18 at 18:05 +0000, Jamie Lokier wrote: > Jeff Moyer wrote: > > James Bottomley writes: > > > > > Not stepping into the debate: I'm happy to see punch go to the mapping > > > data and FITRIM pick it up later. > > > > > > However, I think it's time to question whether we actually still want to > > > allow online discard at all. Most of the benchmarks show it to be a net > > > > Define online discard, please. > > > > > lose to almost everything (either SSD or Thinly Provisioned arrays), so > > > it's become an "enable this to degrade performance" option with no > > > upside. > > > > Some SSDs very much require TRIMming to perform well as they age. If > > you're suggesting that we move from doing discards in journal commits to > > a batched discard, like the one Lukas implemented, then I think that's > > fine. If we need to reintroduce the finer-grained discards due to some > > hardware changes in the future, we can always do that. > > "Growable" virtual disks benefit from it too, if it frees up a lot of space. > > Windows has some ability to trim unused space in NTFS on virtual disks > for this reason; I'm not sure if it's an online or offline procedure. > > Online trim may be slow, but offline would be awfully inconvenient > when an fs is big and needed for a live system, or when it's your root fs. You can call FITRIM from a running system. Infact I run it once per week as a cron job on my (mounted) root fs. -- Markus