From: Dave Chinner Subject: Re: [PATCH] ext2: Use page_mkwrite vma_operations to get mmap write notification. Date: Mon, 23 Jun 2008 08:50:14 +1000 Message-ID: <20080622225014.GC11558@disturbed> References: <1212685513-32237-1-git-send-email-aneesh.kumar@linux.vnet.ibm.com> <20080605123045.445e380a.akpm@linux-foundation.org> <20080611150845.GA21910@skywalker> <20080611120749.d0c5a7de.akpm@linux-foundation.org> <20080612161706.GB12367@duck.suse.cz> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Andrew Morton , "Aneesh Kumar K.V" , cmm@us.ibm.com, linux-ext4@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org To: Jan Kara Return-path: Content-Disposition: inline In-Reply-To: <20080612161706.GB12367@duck.suse.cz> Sender: linux-kernel-owner@vger.kernel.org List-Id: linux-ext4.vger.kernel.org On Thu, Jun 12, 2008 at 06:17:06PM +0200, Jan Kara wrote: > BTW: XFS, OCFS2 or GFS2 define page_mkwrite() in this manner so they do > return SIGBUS when you run out of space when writing to mmapped hole. So > it's not like this change is introducing completely new behavior... I can > understand that we might not want to change the behavior for ext2 or ext3 > but ext4 is IMO definitely free to choose. Yup, and it's the only sane behaviour, IMO. Letting the application continue to oversubscribe filesystem space and then throwing away the data that can't be written well after the fact (potentially after the application has gone away) is a horrendously bad failure mode. This was one of the main publicised features of ->page_mkwrite() - that it would allow up front detection of ENOSPC conditions during mmap writes. I'm extremely surprised to see that this is being considered undesirable after all this time.... Cheers, Dave. -- Dave Chinner david@fromorbit.com