From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wi0-f182.google.com (mail-wi0-f182.google.com [209.85.212.182]) by kanga.kvack.org (Postfix) with ESMTP id E5DE66B0254 for ; Tue, 1 Sep 2015 03:06:10 -0400 (EDT) Received: by wicjd9 with SMTP id jd9so21994427wic.1 for ; Tue, 01 Sep 2015 00:06:10 -0700 (PDT) Received: from newverein.lst.de (verein.lst.de. [213.95.11.211]) by mx.google.com with ESMTPS id em11si1540302wid.64.2015.09.01.00.06.09 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 01 Sep 2015 00:06:09 -0700 (PDT) Date: Tue, 1 Sep 2015 09:06:08 +0200 From: Christoph Hellwig Subject: Re: [PATCH] dax, pmem: add support for msync Message-ID: <20150901070608.GA5482@lst.de> References: <1441047584-14664-1-git-send-email-ross.zwisler@linux.intel.com> <20150831233803.GO3902@dastard> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20150831233803.GO3902@dastard> Sender: owner-linux-mm@kvack.org List-ID: To: Dave Chinner 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 09:38:03AM +1000, Dave Chinner wrote: > On Mon, Aug 31, 2015 at 12:59:44PM -0600, Ross Zwisler wrote: > > For DAX msync we just need to flush the given range using > > wb_cache_pmem(), which is now a public part of the PMEM API. > > This is wrong, because it still leaves fsync() broken on dax. > > Flushing dirty data to stable storage is the responsibility of the > writeback infrastructure, not the VMA/mm infrasrtucture. For non-dax > configurations, msync defers all that to vfs_fsync_range(), because > it has to be implemented there for fsync() to work. > > 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. DAX does call ->fsync before and after this patch. And with all the recent fixes we take care to ensure data is written though the cache for everything but mmap-access. With this patch from Ross we ensure msync writes back the cache before calling ->fsync so that the filesystem can then do it's work like converting unwritten extents. The only downside is that previously on Linux you could always use fsync as a replaement for msymc, which isn't true anymore for DAX. But given that we need the virtual address to write back the cache I can't see how to do this differently given that clwb() needs the user virtual address to flush the cache. -- 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