linux-kernel - Re: [PATCH v4 3/9] mm: pagewalk: Don't split transhuge pmds when a pmd

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Message-ID: <03d85a6a-e24a-82f4-93b8-86584b463471@shipmail.org>
Date:   Wed, 9 Oct 2019 19:03:24 +0200
From:   Thomas Hellström (VMware) 
        <thomas_os@...pmail.org>
To:     Linus Torvalds <torvalds@...ux-foundation.org>,
        "Kirill A. Shutemov" <kirill@...temov.name>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux-MM <linux-mm@...ck.org>,
        Thomas Hellstrom <thellstrom@...are.com>,
        Matthew Wilcox <willy@...radead.org>,
        Will Deacon <will.deacon@....com>,
        Peter Zijlstra <peterz@...radead.org>,
        Rik van Riel <riel@...riel.com>,
        Minchan Kim <minchan@...nel.org>,
        Michal Hocko <mhocko@...e.com>,
        Huang Ying <ying.huang@...el.com>,
        Jérôme Glisse <jglisse@...hat.com>
Subject: Re: [PATCH v4 3/9] mm: pagewalk: Don't split transhuge pmds when a
 pmd_entry is present

On 10/9/19 6:21 PM, Linus Torvalds wrote:
> On Wed, Oct 9, 2019 at 8:27 AM Kirill A. Shutemov <kirill@...temov.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