linux-kernel - Re: [RFC PATCH v2 33/47] userfaultfd: add UFFD_FEATURE_MINOR_HUGETLBFS

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Date:   Thu, 22 Dec 2022 09:30:25 -0500
From:   Peter Xu <peterx@...hat.com>
To:     James Houghton <jthoughton@...gle.com>
Cc:     Mike Kravetz <mike.kravetz@...cle.com>,
        Muchun Song <songmuchun@...edance.com>,
        David Hildenbrand <david@...hat.com>,
        David Rientjes <rientjes@...gle.com>,
        Axel Rasmussen <axelrasmussen@...gle.com>,
        Mina Almasry <almasrymina@...gle.com>,
        Zach O'Keefe <zokeefe@...gle.com>,
        Manish Mishra <manish.mishra@...anix.com>,
        Naoya Horiguchi <naoya.horiguchi@....com>,
        "Dr . David Alan Gilbert" <dgilbert@...hat.com>,
        "Matthew Wilcox (Oracle)" <willy@...radead.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        Baolin Wang <baolin.wang@...ux.alibaba.com>,
        Miaohe Lin <linmiaohe@...wei.com>,
        Yang Shi <shy828301@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH v2 33/47] userfaultfd: add
 UFFD_FEATURE_MINOR_HUGETLBFS_HGM

On Wed, Dec 21, 2022 at 08:24:45PM -0500, James Houghton wrote:
> Not sure what the best name for this flag is either. MADV_ENABLE_HGM
> sounds ok. MADV_HUGETLB_HGM or MADV_HUGETLB_SMALL_PAGES could work
> too. No need to figure it out now.

One more option to consider is MADV_SPLIT (hopefully to be more generic).

We already decided to reuse thp MADV_COLLAPSE, we can also introduce
MADV_SPLIT and leave thp for later if it can be anything helpful (I
remember we used to discuss this for thp split).

For hugetlb one SPLIT should enable hgm advise bit on the vma forever.

Thanks,

-- 
Peter Xu