Re: [PATCH v5 6/7] dax: add recovery_write to dax_iomap_iter in failure path

Christoph Hellwig
2022-02-02T13:44:09Z

On Fri, Jan 28, 2022 at 02:31:49PM -0700, Jane Chu wrote:
> +typedef size_t (*iter_func_t)(struct dax_device *dax_dev, pgoff_t pgoff,
> + void *addr, size_t bytes, struct iov_iter *i);
> static loff_t dax_iomap_iter(const struct iomap_iter *iomi,
> struct iov_iter *iter)
> {
> @@ -1210,6 +1212,7 @@ static loff_t dax_iomap_iter(const struct iomap_iter *iomi,
> ssize_t ret = 0;
> size_t xfer;
> int id;
> + iter_func_t write_func = dax_copy_from_iter;

This use of a function pointer causes indirect call overhead. A simple
"bool in_recovery" or do_recovery does the trick in a way that is
both more readable and generates faster code.

> + if ((map_len == -EIO) && (iov_iter_rw(iter) == WRITE)) {

No need for the braces.

> if (iov_iter_rw(iter) == WRITE)
> - xfer = dax_copy_from_iter(dax_dev, pgoff, kaddr,
> - map_len, iter);
> + xfer = write_func(dax_dev, pgoff, kaddr, map_len, iter);
> else
> xfer = dax_copy_to_iter(dax_dev, pgoff, kaddr,
> map_len, iter);

i.e.

if (iov_iter_rw(iter) == READ)
xfer = dax_copy_to_iter(dax_dev, pgoff, kaddr,
map_len, iter);
else if (unlikely(do_recovery))
xfer = dax_recovery_write(dax_dev, pgoff, kaddr,
map_len, iter);
else
xfer = dax_copy_from_iter(dax_dev, pgoff, kaddr,
map_len, iter);