From: Jamie Lokier Subject: Re: [PATCH 1/2] fs: Do not dispatch FITRIM through separate super_operation Date: Thu, 18 Nov 2010 18:05:57 +0000 Message-ID: <20101118180557.GU22787@shareable.org> 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> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: 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: Jeff Moyer Return-path: Received: from mail2.shareable.org ([80.68.89.115]:59508 "EHLO mail2.shareable.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750917Ab0KRSua (ORCPT ); Thu, 18 Nov 2010 13:50:30 -0500 Content-Disposition: inline In-Reply-To: Sender: linux-ext4-owner@vger.kernel.org List-ID: 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. -- Jamie