On Thu, Nov 24, 2016 at 10:46:33AM +0100, Jan Kara wrote:
> Currently each filesystem (possibly through generic_file_direct_write()
> or iomap_dax_rw()) takes care of invalidating page tables and evicting
Just some nits about the commit message: the DAX I/O path function is now
called dax_iomap_rw(), and no filesystems still use
generic_file_direct_write() for DAX so you can probably remove it from the
changelog - up to you.
Aside from that:
Reviewed-by: Ross Zwisler <ross.zwisler@xxxxxxxxxxxxxxx>
> 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.
>
> Reviewed-by: Christoph Hellwig <hch@xxxxxx>
> Signed-off-by: Jan Kara <jack@xxxxxxx>
> ---
> fs/dax.c | 28 +++++++++++-----------------
> 1 file changed, 11 insertions(+), 17 deletions(-)
>
> diff --git a/fs/dax.c b/fs/dax.c
> index 4534f0e232e9..ddf77ef2ca18 100644
> --- a/fs/dax.c
> +++ b/fs/dax.c
> @@ -984,6 +984,17 @@ dax_iomap_actor(struct inode *inode, loff_t pos, loff_t length, void *data,
> if (WARN_ON_ONCE(iomap->type != IOMAP_MAPPED))
> return -EIO;
>
> + /*
> + * Write can allocate block for an area which has a hole page mapped
> + * into page tables. We have to tear down these mappings so that data
> + * written by write(2) is visible in mmap.
> + */
> + if ((iomap->flags & IOMAP_F_NEW) && inode->i_mapping->nrpages) {
> + invalidate_inode_pages2_range(inode->i_mapping,
> + pos >> PAGE_SHIFT,
> + (end - 1) >> PAGE_SHIFT);
> + }
> +
> while (pos < end) {
> unsigned offset = pos & (PAGE_SIZE - 1);
> struct blk_dax_ctl dax = { 0 };
> @@ -1042,23 +1053,6 @@ dax_iomap_rw(struct kiocb *iocb, struct iov_iter *iter,
> if (iov_iter_rw(iter) == WRITE)
> flags |= IOMAP_WRITE;
>
> - /*
> - * Yes, even DAX files can have page cache attached to them: A zeroed
> - * page is inserted into the pagecache when we have to serve a write
> - * fault on a hole. It should never be dirtied and can simply be
> - * dropped from the pagecache once we get real data for the page.
> - *
> - * XXX: This is racy against mmap, and there's nothing we can do about
> - * it. We'll eventually need to shift this down even further so that
> - * we can check if we allocated blocks over a hole first.
> - */
> - if (mapping->nrpages) {
> - ret = invalidate_inode_pages2_range(mapping,
> - pos >> PAGE_SHIFT,
> - (pos + iov_iter_count(iter) - 1) >> PAGE_SHIFT);
> - WARN_ON_ONCE(ret);
> - }
> -
> while (iov_iter_count(iter)) {
> ret = iomap_apply(inode, pos, iov_iter_count(iter), flags, ops,
> iter, dax_iomap_actor);
> --
> 2.6.6
>
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