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

[Christoph Hellwig]

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.