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

Jan Kara
2023-01-31T12:29:03Z

On Tue 31-01-23 09:32:27, David Hildenbrand wrote:
> On 30.01.23 23:15, Jens Axboe wrote:
> > 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.
> >
>
> Can we just treat the whole acquired/released accounting as a debug
> mechanism to detect missing releases and do it only for debug kernels?

Yes, AFAIK it is just a debug mechanism for helping to find out issues with
page pinning conversions. So I think we can put this behind some debugging
ifdef. John?

Honza
--
Jan Kara <jack@suse.com>
SUSE Labs, CR