From: Ric Wheeler Subject: Re: [patch 0/9] writeback data integrity and other fixes (take 3) Date: Wed, 29 Oct 2008 09:32:19 -0400 Message-ID: <490865E3.8070102@gmail.com> References: <20081028144715.683011000@suse.de> <20081028153953.GB3082@wotan.suse.de> <20081028222746.GB4985@disturbed> <20081029001653.GF15599@wotan.suse.de> <20081029031645.GE4985@disturbed> <20081029091203.GA32545@infradead.org> <20081029092143.GA5953@wotan.suse.de> <20081029094417.GA21824@infradead.org> <20081029103029.GC5953@wotan.suse.de> <20081029122234.GE846@shareable.org> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Cc: Nick Piggin , Christoph Hellwig , linux-nfs@vger.kernel.org, akpm@linux-foundation.org, xfs@oss.sgi.com, linux-fsdevel@vger.kernel.org, Chris Mason To: Jamie Lokier Return-path: Received: from qw-out-2122.google.com ([74.125.92.24]:11771 "EHLO qw-out-2122.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753717AbYJ2Nce (ORCPT ); Wed, 29 Oct 2008 09:32:34 -0400 Received: by qw-out-2122.google.com with SMTP id 3so1611395qwe.37 for ; Wed, 29 Oct 2008 06:32:33 -0700 (PDT) In-Reply-To: <20081029122234.GE846@shareable.org> Sender: linux-nfs-owner@vger.kernel.org List-ID: Jamie Lokier wrote: > Nick Piggin wrote: > >> On Wed, Oct 29, 2008 at 05:44:17AM -0400, Christoph Hellwig wrote: >> >>> On Wed, Oct 29, 2008 at 10:21:43AM +0100, Nick Piggin wrote: >>> >>>> Please do. >>>> >>> Well, there's one stumling block I haven't made progress on yet: >>> >>> I've changed the prototype of ->fsync to lose the dentry as we should >>> always have a valid file struct. Except that nfsd doesn't on >>> directories. So I either need to fake up a file there, or bail out >>> and add a ->dir_sync export operation that needs just a dentry. >>> >> OK. I don't know much about hthat code, but I would think nfsd >> should look as close to the syscall layer as possible. I guess >> there must be something prohibitive (some protocol semantics?). >> >> Is there anything that particularly makes it a file operation >> as opposed to an inode operation? >> > > In principle, is fsync() required to flush all dirty data written > through any file descriptor ever, or just dirty data written through > the file descriptor used for fsync()? > > -- Jamie > -- > http://www.opengroup.org/onlinepubs/009695399/functions/fsync.html Is a pointer to what seems to be the official posix spec for this - it is definitely per file descriptor, not per file system, etc... What can happen by side effect (depending on the implementation) is that you can actually force out all data for any file. I found that you can approach non-fsync speeds for an fsync per file workload by simply writing all of the files out, then going back and fsync'ing them one at a time (last file first makes a bit of a difference). With that technique, you do get the hard promise of full data integrity and high speed. This is useful when you want to do bulk writes (tar, etc) ric