From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751710Ab3HABIJ (ORCPT ); Wed, 31 Jul 2013 21:08:09 -0400 Received: from imap.thunk.org ([74.207.234.97]:37631 "EHLO imap.thunk.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750845Ab3HABIH (ORCPT ); Wed, 31 Jul 2013 21:08:07 -0400 Date: Wed, 31 Jul 2013 21:07:52 -0400 From: "Theodore Ts'o" To: Dave Chinner Cc: Namjae Jeon , adilger.kernel@dilger.ca, bpm@sgi.com, elder@kernel.org, hch@infradead.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-ext4@vger.kernel.org, xfs@oss.sgi.com, a.sangwan@samsung.com, Namjae Jeon Subject: Re: [PATCH 1/3] fs: Introduce new flag FALLOC_FL_COLLAPSE_RANGE Message-ID: <20130801010751.GD11378@thunk.org> Mail-Followup-To: Theodore Ts'o , Dave Chinner , Namjae Jeon , adilger.kernel@dilger.ca, bpm@sgi.com, elder@kernel.org, hch@infradead.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-ext4@vger.kernel.org, xfs@oss.sgi.com, a.sangwan@samsung.com, Namjae Jeon References: <1375281721-15840-1-git-send-email-linkinjeon@gmail.com> <20130731220154.GA11378@thunk.org> <20130801002341.GI7118@dastard> <20130801004645.GC11378@thunk.org> <20130801005447.GS13468@dastard> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20130801005447.GS13468@dastard> User-Agent: Mutt/1.5.21 (2010-09-15) X-SA-Exim-Connect-IP: X-SA-Exim-Mail-From: tytso@thunk.org X-SA-Exim-Scanned: No (on imap.thunk.org); SAEximRunCond expanded to false Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Aug 01, 2013 at 10:54:47AM +1000, Dave Chinner wrote: > > It's not just the range that it's operating on, but also the region > > beyond the range that's been collapsed out. > > Yes, that's part of "the range that it is operating over". > > > A quick eyeball of the patch didn't seem to show any code that handled > > this, which is why I asked the question. > > Right, but really it's the least of the problems I've noticed - the > XFS code is fundamentally broken in many ways - once I've finished > commenting on it, I'll have a quick look to see if the ext4 code has > the same fundamental flaws.... Well, the fundamental flaw of potential races if the file being collapsed has been mmap'ed and there is another process making changes beyond the range that is being collapsed is I suspect one that is going to be very hard to solve, short of not allowing the collapse while there are any read/write mmap's for the file in question. And I would think these sorts of VM issues should be handled with some generic library functions, instead of reimplementing them from scratch in each file system. - Ted