From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pa0-f47.google.com (mail-pa0-f47.google.com [209.85.220.47]) by kanga.kvack.org (Postfix) with ESMTP id C832D6B0254 for ; Tue, 1 Sep 2015 18:49:38 -0400 (EDT) Received: by padhy1 with SMTP id hy1so9873870pad.1 for ; Tue, 01 Sep 2015 15:49:38 -0700 (PDT) Received: from ipmail07.adl2.internode.on.net (ipmail07.adl2.internode.on.net. [150.101.137.131]) by mx.google.com with ESMTP id at5si4382260pbc.108.2015.09.01.15.49.36 for ; Tue, 01 Sep 2015 15:49:38 -0700 (PDT) Date: Wed, 2 Sep 2015 08:49:22 +1000 From: Dave Chinner Subject: Re: [PATCH] dax, pmem: add support for msync Message-ID: <20150901224922.GR3902@dastard> References: <1441047584-14664-1-git-send-email-ross.zwisler@linux.intel.com> <20150831233803.GO3902@dastard> <20150901100804.GA7045@node.dhcp.inet.fi> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20150901100804.GA7045@node.dhcp.inet.fi> Sender: owner-linux-mm@kvack.org List-ID: To: "Kirill A. Shutemov" Cc: Ross Zwisler , linux-kernel@vger.kernel.org, Alexander Viro , Andrew Morton , Christoph Hellwig , Dave Hansen , "H. Peter Anvin" , Hugh Dickins , Ingo Molnar , "Kirill A. Shutemov" , linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-nvdimm@lists.01.org, Matthew Wilcox , Peter Zijlstra , Thomas Gleixner , x86@kernel.org On Tue, Sep 01, 2015 at 01:08:04PM +0300, Kirill A. Shutemov wrote: > On Tue, Sep 01, 2015 at 09:38:03AM +1000, Dave Chinner wrote: > > On Mon, Aug 31, 2015 at 12:59:44PM -0600, Ross Zwisler wrote: > > Even for DAX, msync has to call vfs_fsync_range() for the filesystem to commit > > the backing store allocations to stable storage, so there's not > > getting around the fact msync is the wrong place to be flushing > > DAX mappings to persistent storage. > > Why? > IIUC, msync() doesn't have any requirements wrt metadata, right? Of course it does. If the backing store allocation has not been committed, then after a crash there will be a hole in file and so it will read as zeroes regardless of what data was written and flushed. > > I pointed this out almost 6 months ago (i.e. that fsync was broken) > > anf hinted at how to solve it. Fix fsync, and msync gets fixed for > > free: > > > > https://lists.01.org/pipermail/linux-nvdimm/2015-March/000341.html > > > > I've also reported to Willy that DAX write page faults don't work > > correctly, either. xfstests generic/080 exposes this: a read > > from a page followed immediately by a write to that page does not > > result in ->page_mkwrite being called on the write and so > > backing store is not allocated for the page, nor are the timestamps > > for the file updated. This will also result in fsync (and msync) > > not working properly. > > Is that because XFS doesn't provide vm_ops->pfn_mkwrite? I didn't know that had been committed. I don't recall seeing a pull request with that in it, none of the XFS DAX patches conflicted against it and there's been no runtime errors. I'll fix it up. As such, shouldn't there be a check in the VM (in ->mmap callers) that if we have the vma is returned with VM_MIXEDMODE enabled that ->pfn_mkwrite is not NULL? It's now clear to me that any filesystem that sets VM_MIXEDMODE needs to support both page_mkwrite and pfn_mkwrite, and such a check would have caught this immediately... Cheers, Dave. -- Dave Chinner david@fromorbit.com -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org