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 <20221021163703.3218176-35-jthoughton@google.com> <Y6X1isYeuZMxvDEC@x1n>
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From:   James Houghton <jthoughton@google.com>
Date:   Tue, 27 Dec 2022 11:38:31 -0500
Message-ID: <CADrL8HWfyaQVfcrqrT7Hzt3iHGXiVzNycfCFKpD=YK-YEAX-nA@mail.gmail.com>
Subject: Re: [RFC PATCH v2 34/47] hugetlb: userfaultfd: add support for
 high-granularity UFFDIO_CONTINUE
To:     Peter Xu <peterx@redhat.com>
Cc:     Mike Kravetz <mike.kravetz@oracle.com>,
        Muchun Song <songmuchun@bytedance.com>,
        David Hildenbrand <david@redhat.com>,
        David Rientjes <rientjes@google.com>,
        Axel Rasmussen <axelrasmussen@google.com>,
        Mina Almasry <almasrymina@google.com>,
        "Zach O'Keefe" <zokeefe@google.com>,
        Manish Mishra <manish.mishra@nutanix.com>,
        Naoya Horiguchi <naoya.horiguchi@nec.com>,
        "Dr . David Alan Gilbert" <dgilbert@redhat.com>,
        "Matthew Wilcox (Oracle)" <willy@infradead.org>,
        Vlastimil Babka <vbabka@suse.cz>,
        Baolin Wang <baolin.wang@linux.alibaba.com>,
        Miaohe Lin <linmiaohe@huawei.com>,
        Yang Shi <shy828301@gmail.com>,
        Andrew Morton <akpm@linux-foundation.org>, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org
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On Fri, Dec 23, 2022 at 1:38 PM Peter Xu <peterx@redhat.com> wrote:
>
> James,
>
> On Fri, Oct 21, 2022 at 04:36:50PM +0000, James Houghton wrote:
> > +     bool use_hgm = uffd_ctx_has_hgm(&dst_vma->vm_userfaultfd_ctx) &&
> > +             mode == MCOPY_ATOMIC_CONTINUE;
>
> Do you think in your new version use_hgm can work even for MISSING by
> default?

I don't think so -- UFFDIO_COPY will allocate a hugepage, so I'm not
sure if it makes sense to allow it at high-granularity. If UFFDIO_COPY
didn't allocate a new page, then it could make sense (maybe we'd need
a new ioctl or new UFFDIO_COPY mode?). I think it makes most sense to
add this with another series.

Thanks,
- James