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

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Message-ID: <Y3VkIdVKRuq+fO0N@x1n>
Date:   Wed, 16 Nov 2022 17:28:49 -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 Fri, Oct 21, 2022 at 04:36:49PM +0000, James Houghton wrote:
> Userspace must provide this new feature when it calls UFFDIO_API to
> enable HGM. Userspace can check if the feature exists in
> uffdio_api.features, and if it does not exist, the kernel does not
> support and therefore did not enable HGM.
> 
> Signed-off-by: James Houghton <jthoughton@...gle.com>

It's still slightly a pity that this can only be enabled by an uffd context
plus a minor fault, so generic hugetlb users cannot directly leverage this.

The patch itself looks good.

-- 
Peter Xu