Messages in this thread | | | Date | Wed, 2 Feb 2022 05:44:01 -0800 | From | Christoph Hellwig <> | Subject | Re: [PATCH v5 6/7] dax: add recovery_write to dax_iomap_iter in failure path |
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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);
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