From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Date: Fri, 22 Jan 2016 22:26:19 +1100 From: Dave Chinner To: "Darrick J. Wong" Cc: Matthew Wilcox , Andrew Morton , Matthew Wilcox , linux-mm@kvack.org, linux-nvdimm@ml01.01.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, x86@kernel.org Subject: Re: [PATCH v3 0/8] Support for transparent PUD pages for DAX files Message-ID: <20160122112619.GC6033@dastard> References: <1452282592-27290-1-git-send-email-matthew.r.wilcox@intel.com> <20160115194150.GA5751@birch.djwong.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20160115194150.GA5751@birch.djwong.org> Sender: owner-linux-mm@kvack.org List-ID: On Fri, Jan 15, 2016 at 11:41:50AM -0800, Darrick J. Wong wrote: > On Fri, Jan 08, 2016 at 02:49:44PM -0500, Matthew Wilcox wrote: > > From: Matthew Wilcox > > > > Andrew, I think this is ready for a spin in -mm. > > > > v3: Rebased against current mmtom > > v2: Reduced churn in filesystems by switching to ->huge_fault interface > > Addressed concerns from Kirill > > > > We have customer demand to use 1GB pages to map DAX files. Unlike the 2MB > > page support, the Linux MM does not currently support PUD pages, so I have > > attempted to add support for the necessary pieces for DAX huge PUD pages. > > > > Filesystems still need work to allocate 1GB pages. With ext4, I can > > only get 16MB of contiguous space, although it is aligned. With XFS, > > I can get 80MB less than 1GB, and it's not aligned. The XFS problem > > may be due to the small amount of RAM in my test machine. > > "It's not aligned"... I don't know the details of what you're trying to do, but > are you trying to create a file where each GB of logical address space maps to > a contiguous GB of physical space, and both logical and physical offsets align > to a 1GB boundary? > > If the XFS is formatted with stripe unit/width of 1G, an extent size hint of 1G > is put on the file, and the whole file is allocated in 1G chunks, I think > you're supposed to be able to make the above happen: If you really, really want to guarantee 1GB aligned extents for file data on XFS, use the realtime device with a 1GB extent size..... 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