Re: [PATCH 6/6] dax: Avoid page invalidation races and unnecessary radix tree traversals

[Christoph Hellwig <hch-wEGCiKHe2LqWVfeAwA7xHQ@public.gmane.org>]

On Tue, Sep 27, 2016 at 06:43:35PM +0200, Jan Kara wrote:
> Currently each filesystem (possibly through generic_file_direct_write()
> or iomap_dax_rw()) takes care of invalidating page tables and evicting
> hole pages from the radix tree when write(2) to the file happens. This
> invalidation is only necessary when there is some block allocation
> resulting from write(2). Furthermore in current place the invalidation
> is racy wrt page fault instantiating a hole page just after we have
> invalidated it.
> 
> So perform the page invalidation inside dax_do_io() where we can do it
> only when really necessary and after blocks have been allocated so
> nobody will be instantiating new hole pages anymore.
> 
> Signed-off-by: Jan Kara <jack-AlSwsSmVLrQ@public.gmane.org>

This looks fine with the comment from Dave addressed:

Reviewed-by: Christoph Hellwig <hch-jcswGhMUV9g@public.gmane.org>

> +				if (buffer_new(bh) &&
> +				    inode->i_mapping->nrpages) {

Btw, it would be nice if the nrpages check could move into
invalidate_inode_pages2_range instead of having to bother with it in
the callers.