Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751743AbXBVRxd (ORCPT ); Thu, 22 Feb 2007 12:53:33 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751746AbXBVRxd (ORCPT ); Thu, 22 Feb 2007 12:53:33 -0500 Received: from mx1.redhat.com ([66.187.233.31]:59888 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751742AbXBVRxc (ORCPT ); Thu, 22 Feb 2007 12:53:32 -0500 Message-ID: <45DDD498.9050202@redhat.com> Date: Thu, 22 Feb 2007 12:36:24 -0500 From: Peter Staubach User-Agent: Thunderbird 1.5.0.9 (X11/20061215) MIME-Version: 1.0 To: Miklos Szeredi CC: akpm@linux-foundation.org, hugh@veritas.com, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] update ctime and mtime for mmaped write References: <45DC8A47.5050900@redhat.com> <45DC9581.4070909@redhat.com> In-Reply-To: Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2767 Lines: 81 Miklos Szeredi wrote: >>>>> Inspired by Peter Staubach's patch and the resulting comments. >>>>> >>>>> >>>>> >>>>> >>>> An updated version of the original patch was submitted to LKML >>>> yesterday... :-) >>>> >>>> >>> Strange coincidence :) >>> >>> >>> >>>>> file = vma->vm_file; >>>>> start = vma->vm_end; >>>>> + mapping_update_time(file); >>>>> if ((flags & MS_SYNC) && file && >>>>> (vma->vm_flags & VM_SHARED)) { >>>>> get_file(file); >>>>> >>>>> >>>>> >>>> It seems to me that this might lead to file times being updated for >>>> non-MAP_SHARED mappings. >>>> >>>> >>> In theory no, because the COW-ed pages become anonymous and are not >>> part of the original mapping any more. >>> >>> >>> >> I must profess to having a incomplete understanding of all of this >> support, but then why would it be necessary to test VM_SHARED at >> this point in msync()? >> > > That's basically just an optimization. If it wasn't there, then data > from a another (shared) mapping could be written back, which is not > wrong, but not required either. > > >> I ran into problems early on with file times being updated incorrectly >> so I am a little sensitive this aspect. >> >> >>>>> +int set_page_dirty_mapping(struct page *page); >>>>> >>>>> >>>>> >>>> This aspect of the design seems intrusive to me. I didn't see a strong >>>> reason to introduce new versions of many of the routines just to handle >>>> these semantics. What motivated this part of your design? Why the new >>>> _mapping versions of routines? >>>> >>>> >>> Because there's no way to know inside the set_page_dirty() functions >>> if the dirtying comes from a memory mapping or from a modification >>> through a normal write(). And they have different semantics, for >>> write() the modification times are updated immediately. >>> >> Perhaps I didn't understand what page_mapped() does, but it does seem to >> have the right semantics as far as I could see. >> > > The problems will start, when you have a file that is both mapped and > modified with write(). Then the dirying from the write() will set the > flag, and that will have undesirable consequences. I don't think that I quite follow the logic. The dirtying from write() will set the flag, but then the mtime will get updated and the flag will be cleared by the hook in file_update_time(). Right? Thanx... ps - 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/