From: "Amit K. Arora" Subject: Re: Testing ext4 persistent preallocation patches for 64 bit features Date: Thu, 8 Feb 2007 14:22:31 +0530 Message-ID: <20070208085231.GA15964@amitarora.in.ibm.com> References: <20070117094658.GA17390@amitarora.in.ibm.com> <20070207074801.GA5419@amitarora.in.ibm.com> <1170836750.4355.36.camel@localhost.localdomain> <20070207103622.GA6328@in.ibm.com> <20070207211117.GE6565@schatzie.adilger.int> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: suparna@in.ibm.com, cmm@us.ibm.com, linux-ext4@vger.kernel.org, linux-fsdevel@vger.kernel.org, alex@clusterfs.com, suzuki@in.ibm.com To: adilger@clusterfs.com Return-path: Received: from e3.ny.us.ibm.com ([32.97.182.143]:36097 "EHLO e3.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1423085AbXBHIwl (ORCPT ); Thu, 8 Feb 2007 03:52:41 -0500 Content-Disposition: inline In-Reply-To: <20070207211117.GE6565@schatzie.adilger.int> Sender: linux-ext4-owner@vger.kernel.org List-Id: linux-ext4.vger.kernel.org On Wed, Feb 07, 2007 at 02:11:17PM -0700, Andreas Dilger wrote: > On Feb 07, 2007 16:06 +0530, Suparna Bhattacharya wrote: > > On Wed, Feb 07, 2007 at 12:25:50AM -0800, Mingming Cao wrote: > > > - disable preallocation if the filesystem free blocks is under some low > > > watermarks, to save space for near future real block allocation? > > > > A policy decision like this is probably worth a discussion during today's call. > > > > > - is de-preallocation something worth doing? > > As discussed in the call - I don't think we can remove preallocations. > The whole point of database preallocation is to guarantee that this space > is available in the filesystem when writing into a file at random offsets > (which would otherwise be sparse). > > Similarly, persistent preallocation shouldn't be considered differently > than an efficient way of doing zero filling of blocks. At least that is > my understanding... Is this code implementing the "uninitialized extents" > for databases (via explicit preallocation via fallocate/ioctl) so that > they don't have to zero-fill large files, or is there also automatic > preallocation of space to files (e.g. for O_APPEND files)? You are right. There is no automatic preallocation of space being done here. This code just implements the explicit (persistent) preallocation of blocks via ioctl. -- Regards, Amit Arora