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Date: Tue, 25 Jul 2017 14:15:22 +0200 From: Christoph Hellwig <hch@....de> To: Jan Kara <jack@...e.cz> Cc: Christoph Hellwig <hch@....de>, "Kirill A. Shutemov" <kirill@...temov.name>, Ross Zwisler <ross.zwisler@...ux.intel.com>, Andrew Morton <akpm@...ux-foundation.org>, linux-kernel@...r.kernel.org, "Darrick J. Wong" <darrick.wong@...cle.com>, Theodore Ts'o <tytso@....edu>, Alexander Viro <viro@...iv.linux.org.uk>, Andreas Dilger <adilger.kernel@...ger.ca>, Dan Williams <dan.j.williams@...el.com>, Dave Chinner <david@...morbit.com>, Ingo Molnar <mingo@...hat.com>, Jonathan Corbet <corbet@....net>, Matthew Wilcox <mawilcox@...rosoft.com>, Steven Rostedt <rostedt@...dmis.org>, linux-doc@...r.kernel.org, linux-ext4@...r.kernel.org, linux-fsdevel@...r.kernel.org, linux-mm@...ck.org, linux-nvdimm@...ts.01.org, linux-xfs@...r.kernel.org Subject: Re: [PATCH v5 1/5] mm: add vm_insert_mixed_mkwrite() On Tue, Jul 25, 2017 at 11:35:08AM +0200, Jan Kara wrote: > On Tue 25-07-17 10:01:58, Christoph Hellwig wrote: > > On Tue, Jul 25, 2017 at 01:14:00AM +0300, Kirill A. Shutemov wrote: > > > I guess it's up to filesystem if it wants to reuse the same spot to write > > > data or not. I think your assumptions works for ext4 and xfs. I wouldn't > > > be that sure for btrfs or other filesystems with CoW support. > > > > Or XFS with reflinks for that matter. Which currently can't be > > combined with DAX, but I had a somewhat working version a few month > > ago. > > But in cases like COW when the block mapping changes, the process > must run unmap_mapping_range() before installing the new PTE so that all > processes mapping this file offset actually refault and see the new > mapping. So this would go through pte_none() case. Am I missing something? Yes, for DAX COW mappings we'd probably need something like this, unlike the pagecache COW handling for which only the underlying block change, but not the page.
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