From: Amir Goldstein Subject: Re: Proposed design for big allocation blocks for ext4 Date: Fri, 25 Feb 2011 23:24:33 +0200 Message-ID: References: <1F9A85BD-4B5E-488C-B903-0AE17AACF2B7@dilger.ca> <20110225190436.GZ2924@thunk.org> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: QUOTED-PRINTABLE Cc: Andreas Dilger , linux-ext4@vger.kernel.org To: "Ted Ts'o" Return-path: Received: from mail-qw0-f46.google.com ([209.85.216.46]:63566 "EHLO mail-qw0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754671Ab1BYVYe convert rfc822-to-8bit (ORCPT ); Fri, 25 Feb 2011 16:24:34 -0500 Received: by qwd7 with SMTP id 7so1555326qwd.19 for ; Fri, 25 Feb 2011 13:24:34 -0800 (PST) In-Reply-To: <20110225190436.GZ2924@thunk.org> Sender: linux-ext4-owner@vger.kernel.org List-ID: On Fri, Feb 25, 2011 at 9:04 PM, Ted Ts'o wrote: > On Fri, Feb 25, 2011 at 08:05:43PM +0200, Amir Goldstein wrote: >> >> I like your design. very KISS indeed. >> I am just wondering why should BIGALLOC be INCOMPAT and not RO_COMPA= T? >> After all, ro mount doesn't allocate and RO_COMPAT features are so m= uc >> =A0nicer... > > I can try to make it be RO_COMPAT, but one thing my design changes is > that a block group will contain 32768 allocation blocks; so assuming = a > 4k blocks, instead of a block group containing a maximum of 32,768 4k > blocks comprising 128 MB, a block group would now contain 32,768 1M > blocks, or 32 GiB, or 8,388,608 4k blocks. > > I'm pretty sure that existing kernels have superblock sanity checks > that will barf if they see this. =A0Still, yeah, I can try allocating > this as a ROCOMPAT feature, and later on, if people really care, they > can patch older kernels so they won't freak out when they see a > BigAlloc file system and can thus successfully mount it read-only. > > (Right now existing kernels will complain when s_blocks_per_group is > greater than blocksize*8.) > no problem. just rename s_blocks_per_group to s_bigblocks_per_group to be compatible with old kernels. -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" i= n the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html