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Date: Wed, 2 Feb 2022 05:44:01 -0800 From: Christoph Hellwig <hch@...radead.org> To: Jane Chu <jane.chu@...cle.com> Cc: david@...morbit.com, djwong@...nel.org, dan.j.williams@...el.com, hch@...radead.org, vishal.l.verma@...el.com, dave.jiang@...el.com, agk@...hat.com, snitzer@...hat.com, dm-devel@...hat.com, ira.weiny@...el.com, willy@...radead.org, vgoyal@...hat.com, linux-fsdevel@...r.kernel.org, nvdimm@...ts.linux.dev, linux-kernel@...r.kernel.org, linux-xfs@...r.kernel.org Subject: Re: [PATCH v5 6/7] dax: add recovery_write to dax_iomap_iter in failure path 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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