Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Date:   Fri, 23 Dec 2022 13:38:02 -0500
From:   Peter Xu <peterx@redhat.com>
To:     James Houghton <jthoughton@google.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
Subject: Re: [RFC PATCH v2 34/47] hugetlb: userfaultfd: add support for
 high-granularity UFFDIO_CONTINUE
Message-ID: <Y6X1isYeuZMxvDEC@x1n>
References: <20221021163703.3218176-1-jthoughton@google.com>
 <20221021163703.3218176-35-jthoughton@google.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=utf-8
Content-Disposition: inline
In-Reply-To: <20221021163703.3218176-35-jthoughton@google.com>
Precedence: bulk

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 had a feeling that the major components are ready for that anyway.  Then
no matter how HGM is enabled (assuming it'll switch to MADV, or even one
can just register with MISSING+MINOR and enable the uffd HGM feature), an
existing MISSING only app can easily switch to HGM support if it's on huge
pages.

Thanks,

-- 
Peter Xu