Re: [PATCH 3/6] drivers/IB,qib: do not use mmap_sem

Jan Kara
2019-01-31T10:04:05Z

On Wed 30-01-19 18:01:33, Weiny, Ira wrote:
> >
> > On Tue, Jan 29, 2019 at 10:50:05AM -0800, Ira Weiny wrote:
> > > > .. and I'm looking at some of the other conversions here.. *most
> > > > likely* any caller that is manipulating rlimit for get_user_pages
> > > > should really be calling get_user_pages_longterm, so they should not
> > > > be converted to use _fast?
> > >
> > > Is this a question? I'm not sure I understand the meaning here?
> >
> > More an invitation to disprove the statement
>
> Generally I agree. But would be best if we could get fast GUP for
> performance. I have not worked out if that will be possible with the
> final "longterm" solutions.

Initially probably not, longer-term it might be added if there are
performance data supporting that (i.e., showing real workload that would
benefit). In principle there's nothing that would prevent gup_fast like
functionality for long-term pins but I expect there will be always
additional overhead (compared to plain gup_fast()) of establishing
something like leases to identify long-term pins. But we haven't figured
out the details yet. For now we concentrate on fixing short-term pins and
issues with those.

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