Re: [GIT PULL] iov_iter: Improve page extraction (pin or just list)

Jens Axboe
2023-01-30T22:15:47Z

On 1/30/23 3:12 PM, David Howells wrote:
> John Hubbard <jhubbard@nvidia.com> wrote:
>
>> This is something that we say when adding pin_user_pages_fast(),
>> yes. I doubt that I can quickly find the email thread, but we
>> measured it and weren't immediately able to come up with a way
>> to make it faster.
>
> percpu counters maybe - add them up at the point of viewing?

They are percpu, see my last email. But for every 108 changes (on
my system), they will do two atomic_long_adds(). So not very
useful for anything but low frequency modifications.

--
Jens Axboe