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Subject: Re: [PATCH v4 3/9] mm: pagewalk: Don't split transhuge pmds when a
 pmd_entry is present
To:     Linus Torvalds <torvalds@linux-foundation.org>,
        "Kirill A. Shutemov" <kirill@shutemov.name>
Cc:     Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Linux-MM <linux-mm@kvack.org>,
        Thomas Hellstrom <thellstrom@vmware.com>,
        Matthew Wilcox <willy@infradead.org>,
        Will Deacon <will.deacon@arm.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Rik van Riel <riel@surriel.com>,
        Minchan Kim <minchan@kernel.org>,
        Michal Hocko <mhocko@suse.com>,
        Huang Ying <ying.huang@intel.com>,
        =?UTF-8?B?SsOpcsO0bWUgR2xpc3Nl?= <jglisse@redhat.com>
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From:   =?UTF-8?Q?Thomas_Hellstr=c3=b6m_=28VMware=29?= 
        <thomas_os@shipmail.org>
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Date:   Wed, 9 Oct 2019 19:03:24 +0200
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On 10/9/19 6:21 PM, Linus Torvalds wrote:
> On Wed, Oct 9, 2019 at 8:27 AM Kirill A. Shutemov <kirill@shutemov.name> wrote:
>> Do we have any current user that expect split_huge_pmd() in this scenario.
> No. There are no current users of the pmd callback and the pte
> callback at all, that I could find.
>
> But it looks like the new drm use does want a "I can't handle the
> hugepage, please split it and I'll fo the ptes instead".
>
Nope, it handles the hugepages by ignoring them, since they should be 
read-only, but if pmd_entry() was called with something else than a 
hugepage, then it requests the fallback, but never a split.

/Thomas