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fuse: Move prefaulting out of hot write path

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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: Dave Hansen <dave.hansen@linux.intel.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
This commit is contained in:
Dave Hansen 2025-01-29 10:17:56 -08:00 committed by Miklos Szeredi
parent 0486b1832d
commit faa794dd2e
1 changed files with 10 additions and 4 deletions
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14
fs/fuse/file.c
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@ -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;
}