Re: [PATCH 17/17] xfs: support for synchronous DAX faults

From: Christoph Hellwig <hch(a)lst.de&gt; Return IOMAP_F_DIRTY from xfs_file_iomap_begin() when asked to prepare blocks for writing and the inode is pinned, and has dirty fields other than the timestamps. In __xfs_filemap_fault() we then detect this case and call dax_finish_sync_fault() to make sure all metadata is committed, and to insert the page table entry. Note that this will also dirty corresponding radix tree entry which is what we want - fsync(2) will still provide data integrity guarantees for applications not using userspace flushing. And applications using userspace flushing can avoid calling fsync(2) and thus avoid the performance overhead. [JK: Added VM_SYNC flag handling] Signed-off-by: Christoph Hellwig <hch(a)lst.de&gt; Signed-off-by: Jan Kara <jack(a)suse.cz&gt;