From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Date: Mon, 4 Jan 2016 22:41:21 +0200 From: "Kirill A. Shutemov" To: Dave Chinner Cc: Matthew Wilcox , Matthew Wilcox , linux-mm@kvack.org, linux-nvdimm@lists.01.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, x86@kernel.org Subject: Re: [PATCH 7/8] xfs: Support for transparent PUD pages Message-ID: <20160104204121.GD13515@node.shutemov.name> References: <1450974037-24775-1-git-send-email-matthew.r.wilcox@intel.com> <1450974037-24775-8-git-send-email-matthew.r.wilcox@intel.com> <20151230233007.GA6682@dastard> <20160102164309.GK2457@linux.intel.com> <20160103203356.GD6682@dastard> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20160103203356.GD6682@dastard> Sender: owner-linux-mm@kvack.org List-ID: On Mon, Jan 04, 2016 at 07:33:56AM +1100, Dave Chinner wrote: > On Sat, Jan 02, 2016 at 11:43:09AM -0500, Matthew Wilcox wrote: > > On Thu, Dec 31, 2015 at 10:30:27AM +1100, Dave Chinner wrote: > > > > @@ -1637,6 +1669,7 @@ xfs_filemap_pfn_mkwrite( > > > > static const struct vm_operations_struct xfs_file_vm_ops = { > > > > .fault = xfs_filemap_fault, > > > > .pmd_fault = xfs_filemap_pmd_fault, > > > > + .pud_fault = xfs_filemap_pud_fault, > > > > > > This is getting silly - we now have 3 different page fault handlers > > > that all do exactly the same thing. Please abstract this so that the > > > page/pmd/pud is transparent and gets passed through to the generic > > > handler code that then handles the differences between page/pmd/pud > > > internally. > > > > > > This, after all, is the original reason that the ->fault handler was > > > introduced.... > > > > I agree that it's silly, but this is the direction I was asked to go in by > > the MM people at the last MM summit. There was agreement that this needs > > to be abstracted, but that should be left for a separate cleanup round. > > Ok, so it's time to abstract it now, before we end up with another > round of broken filesystem code (like the first attempts at the > XFS pmd_fault code). > > > I did prototype something I called a vpte (virtual pte), but that's very > > much on the back burner for now. > > It's trivial to pack the parameters for pmd_fault and pud_fault > into the struct vm_fault - all you need to do is add pmd_t/pud_t > pointers to the structure, and everything else can be put into > existing members of that structure. There's no need for a "virtual > pte" type anywhere - you can do this effectively with an anonymous > union for the pte/pmd/pud pointer and a flag to indicate the fault > type. > > Then in __dax_fault() you can check vmf->flags and call the > appropriate __dax_p{te,md,ud}_fault function, all without the > filesystem having to care about the different fault types. Similar > can be done with filemap_fault() - if it gets pmd/pud fault flags > set it can just reject them as they should never occur right now... I think the first 4 patches of my hugetmpfs RFD patchset[1] are relevant here. Looks like it shouldn't be a big deal to extend the approach to cover DAX case. [1] http://lkml.kernel.org./r/1447889136-6928-1-git-send-email-kirill.shutemov@linux.intel.com -- Kirill A. Shutemov -- 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