Re: [PATCH] tmpfs: fix regressions from wider use of ZERO_PAGE

Christoph Hellwig
2022-04-09T05:07:29Z

On Fri, Apr 08, 2022 at 01:38:41PM -0700, Hugh Dickins wrote:
> + } else if (iter_is_iovec(to)) {
> + /*
> + * Copy to user tends to be so well optimized, but
> + * clear_user() not so much, that it is noticeably
> + * faster to copy the zero page instead of clearing.
> + */
> + ret = copy_page_to_iter(ZERO_PAGE(0), offset, nr, to);

Is the offset and length guaranteed to be less than PAGE_SIZE here?

Either way I'd rather do this optimization in iov_iter_zero rather
than hiding it in tmpfs.