From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Date: Wed, 28 Sep 2016 07:47:20 +1000 From: Dave Chinner To: Ross Zwisler Cc: linux-kernel@vger.kernel.org, Theodore Ts'o , Alexander Viro , Andreas Dilger , Andrew Morton , Christoph Hellwig , Dan Williams , Jan Kara , Matthew Wilcox , linux-ext4@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-nvdimm@lists.01.org, linux-xfs@vger.kernel.org Subject: Re: [PATCH v3 04/11] ext2: remove support for DAX PMD faults Message-ID: <20160927214720.GD27872@dastard> References: <1475009282-9818-1-git-send-email-ross.zwisler@linux.intel.com> <1475009282-9818-5-git-send-email-ross.zwisler@linux.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1475009282-9818-5-git-send-email-ross.zwisler@linux.intel.com> Sender: owner-linux-mm@kvack.org List-ID: On Tue, Sep 27, 2016 at 02:47:55PM -0600, Ross Zwisler wrote: > DAX PMD support was added via the following commit: > > commit e7b1ea2ad658 ("ext2: huge page fault support") > > I believe this path to be untested as ext2 doesn't reliably provide block > allocations that are aligned to 2MiB. In my testing I've been unable to > get ext2 to actually fault in a PMD. It always fails with a "pfn > unaligned" message because the sector returned by ext2_get_block() isn't > aligned. > > I've tried various settings for the "stride" and "stripe_width" extended > options to mkfs.ext2, without any luck. > > Since we can't reliably get PMDs, remove support so that we don't have an > untested code path that we may someday traverse when we happen to get an > aligned block allocation. This should also make 4k DAX faults in ext2 a > bit faster since they will no longer have to call the PMD fault handler > only to get a response of VM_FAULT_FALLBACK. > > Signed-off-by: Ross Zwisler .... > @@ -154,7 +133,6 @@ static int ext2_dax_pfn_mkwrite(struct vm_area_struct *vma, > > static const struct vm_operations_struct ext2_dax_vm_ops = { > .fault = ext2_dax_fault, > - .pmd_fault = ext2_dax_pmd_fault, > .page_mkwrite = ext2_dax_fault, > .pfn_mkwrite = ext2_dax_pfn_mkwrite, > }; Would it be better to put a comment mentioning this here? So as the years go by, this reminds people not to bother trying to implement it? /* * .pmd_fault is not supported for DAX because allocation in ext2 * cannot be reliably aligned to huge page sizes and so pmd faults * will always fail and fail back to regular faults. */ -- 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