linux-kernel - Re: [RFC PATCH 00/26] hugetlb: Introduce HugeTLB high-granularity mapping

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Date:   Mon, 27 Jun 2022 18:56:09 +0100
From:   "Dr. David Alan Gilbert" <dgilbert@...hat.com>
To:     James Houghton <jthoughton@...gle.com>
Cc:     Matthew Wilcox <willy@...radead.org>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Muchun Song <songmuchun@...edance.com>,
        Peter Xu <peterx@...hat.com>,
        David Hildenbrand <david@...hat.com>,
        David Rientjes <rientjes@...gle.com>,
        Axel Rasmussen <axelrasmussen@...gle.com>,
        Mina Almasry <almasrymina@...gle.com>,
        Jue Wang <juew@...gle.com>,
        Manish Mishra <manish.mishra@...anix.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH 00/26] hugetlb: Introduce HugeTLB high-granularity
 mapping

* James Houghton (jthoughton@...gle.com) wrote:
> On Fri, Jun 24, 2022 at 11:29 AM Matthew Wilcox <willy@...radead.org> wrote:
> >
> > On Fri, Jun 24, 2022 at 05:36:30PM +0000, James Houghton wrote:
> > > [1] This used to be called HugeTLB double mapping, a bad and confusing
> > >     name. "High-granularity mapping" is not a great name either. I am open
> > >     to better names.
> >
> > Oh good, I was grinding my teeth every time I read it ;-)
> >
> > How does "Fine granularity" work for you?
> > "sub-page mapping" might work too.
> 
> "Granularity", as I've come to realize, is hard to say, so I think I
> prefer sub-page mapping. :) So to recap the suggestions I have so far:
> 
> 1. Sub-page mapping
> 2. Granular mapping
> 3. Flexible mapping
> 
> I'll pick one of these (or maybe some other one that works better) for
> the next version of this series.

<shrug> Just a name; SPM might work (although may confuse those
architectures which had subprotection for normal pages), and at least
we can mispronounce it.

In 14/26 your commit message says:

  1. Faults can be passed to handle_userfault. (Userspace will want to
     use UFFD_FEATURE_REAL_ADDRESS to get the real address to know which
     region they should be call UFFDIO_CONTINUE on later.)

can you explain what that new UFFD_FEATURE does?

Dave

-- 
Dr. David Alan Gilbert / dgilbert@...hat.com / Manchester, UK