From: Josef 'Jeff' Sipek Subject: Re: [PATCH 1/4] vfs: vfs-level fiemap interface Date: Sat, 20 Sep 2008 12:47:59 -0400 Message-ID: <20080920164759.GY27404@josefsipek.net> References: <1221331767-16870-1-git-send-email-tytso@mit.edu> <2EC8176B-0AFA-4B36-A2F5-E51753A576A5@cam.ac.uk> <20080913212903.GF26128@mit.edu> <20080914134859.GB21746@infradead.org> <20080914175810.GB13074@mit.edu> <20080915144948.GB16491@infradead.org> <20080915175305.GS4563@wotan.suse.de> <20080916213106.GA10562@mit.edu> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Mark Fasheh , Christoph Hellwig , Anton Altaparmakov , linux-fsdevel@vger.kernel.org, linux-ext4@vger.kernel.org, akpm@linuxfoundation.org To: Theodore Tso Return-path: Content-Disposition: inline In-Reply-To: <20080916213106.GA10562@mit.edu> Sender: linux-fsdevel-owner@vger.kernel.org List-Id: linux-ext4.vger.kernel.org On Tue, Sep 16, 2008 at 05:31:07PM -0400, Theodore Tso wrote: > On Mon, Sep 15, 2008 at 10:53:05AM -0700, Mark Fasheh wrote: > > On Mon, Sep 15, 2008 at 10:49:48AM -0400, Christoph Hellwig wrote: > > > I agree to you (or someone elses - don't remember anymore) suggestion > > > to put in more padding so we can add fields later. I strongly disagree > > > putting in features now that we neither have a user, nor a usecase or > > > testcase for. > > > > So, how about another 64 bits of padding in struct fiemap_extent? That could > > help cover future uses like compression, which might require another 64 bit > > offset field - we only have 32 bits of reserved space there right now. > > What I'd recommend is a 56 byte structure: Why not just make it 64 bytes? Sure, that's 8 extra bytes, but I find the power-of-2 size (and the extra space) comforting. (AFAIK, slab allocators will give you 64 bytes anyway; and I expect something similar on the user-space side of things.) ... > Yeah, it's a little extra memory per extent, but filesystems seem to > always invent new things, and it seem spretty clear that we have at > least two extensions on deck (compression, multiple storage devices) > both of which have at least one implementation that are either in the > kernel or will likely enter the kernel. So it's likely that there is > something that we may have missed, and leaving a little extra space > doesn't actually cost us that much. Right. Josef 'Jeff' Sipek. -- Once you have their hardware. Never give it back. (The First Rule of Hardware Acquisition)