Commit faa794dd authored by Dave Hansen's avatar Dave Hansen Committed by Miklos Szeredi
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fuse: Move prefaulting out of hot write path 



Prefaulting the write source buffer incurs an extra userspace access
in the common fast path. Make fuse_fill_write_pages() consistent with
generic_perform_write(): only touch userspace an extra time when
copy_folio_from_iter_atomic() has failed to make progress.

Signed-off-by: default avatarDave Hansen <dave.hansen@linux.intel.com>
Signed-off-by: default avatarMiklos Szeredi <mszeredi@redhat.com>
parent 0486b183

fs/fuse/file.c

+10 −4
Original line number Diff line number Diff line
@@ -1243,10 +1243,6 @@ static ssize_t fuse_fill_write_pages(struct fuse_io_args *ia, 
		bytes = min_t(size_t, bytes, fc->max_write - count);



 again:

		err = -EFAULT;

		if (fault_in_iov_iter_readable(ii, bytes))

			break;



		folio = __filemap_get_folio(mapping, index, FGP_WRITEBEGIN,

					    mapping_gfp_mask(mapping));

		if (IS_ERR(folio)) {
@@ -1263,6 +1259,16 @@ static ssize_t fuse_fill_write_pages(struct fuse_io_args *ia, 
		if (!tmp) {

			folio_unlock(folio);

			folio_put(folio);



			/*

			 * Ensure forward progress by faulting in

			 * while not holding the folio lock:

			 */

			if (fault_in_iov_iter_readable(ii, bytes)) {

				err = -EFAULT;

				break;

			}



			goto again;

		}