Re: [PATCH 02/11] mm: call import_iovec() instead of rw_copy_check_uvector() in process_vm_rw()

[Al Viro]

On Mon, Sep 21, 2020 at 03:21:35PM +0000, David Laight wrote:

> You really don't want to be looping through the array twice.

Profiles, please.

> I think the 'length' check can be optimised to do something like:
> 	for (...) {
> 		ssize_t len = (ssize_t)iov[seg].iov_len;
> 		ret += len;
> 		len_hi += (unsigned long)len >> 20;
> 	}
> 	if (len_hi) {
> 		/* Something potentially odd in the lengths.
> 		 * Might just be a very long fragment.
> 		 * Check the individial values. */
> 		Add the exiting loop here.
> 	}

Far too ugly to live.