Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id ; Mon, 4 Mar 2002 02:56:12 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id ; Mon, 4 Mar 2002 02:56:03 -0500 Received: from parcelfarce.linux.theplanet.co.uk ([195.92.249.252]:37899 "EHLO www.linux.org.uk") by vger.kernel.org with ESMTP id ; Mon, 4 Mar 2002 02:55:45 -0500 Message-ID: <3C83280A.A8CF7CC8@zip.com.au> Date: Sun, 03 Mar 2002 23:53:46 -0800 From: Andrew Morton X-Mailer: Mozilla 4.79 [en] (X11; U; Linux 2.4.19-pre2 i686) X-Accept-Language: en MIME-Version: 1.0 To: Andreas Dilger CC: Daniel Phillips , lkml Subject: Re: [patch] delayed disk block allocation In-Reply-To: <3C7F3B4A.41DB7754@zip.com.au> <20020304050450.GF353@matchmail.com>, <20020304050450.GF353@matchmail.com>; from mfedyk@matchmail.com on Sun, Mar 03, 2002 at 09:04:50PM -0800 <20020303223103.J4188@lynx.adilger.int> Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Andreas Dilger wrote: > > Actually, there are a whole bunch of performance issues with 1kB block > ext2 filesystems. I don't see any new problems with file tails here. They're catered for OK. What I have not catered for is file holes. With the delalloc patches, whole pages are always written out (except for at eof). So if your file has lots of very small non-holes in it, these will become larger non-holes. If we're serious about 64k PAGE_CACHE_SIZE then this becomes more of a problem. In the worst case, a file which used to consist of 4k block | (1 meg - 4k) hole | 4k block | (1 meg - 4k) hole | ... will become: 64k block | (1 meg - 64k) hole | 64k block | (1 meg - 64k hole) | ... Which is a *lot* more disk space. It'll happen right now, if the file is written via mmap. But with no-buffer-head delayed allocate, it'll happen with write(2) as well. Is such space wastage on sparse files a showstopper? Maybe, but probably not if there is always at least one filesystem which handles this scenario well, because it _is_ a specialised scenario. - - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/