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    SubjectRe: [PATCH v4] mm/thp: fix "mm: thp: kill __transhuge_page_enabled()"
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    On 25.09.23 22:01, Zach O'Keefe wrote:
    > The 6.0 commits:
    >
    > commit 9fec51689ff6 ("mm: thp: kill transparent_hugepage_active()")
    > commit 7da4e2cb8b1f ("mm: thp: kill __transhuge_page_enabled()")
    >
    > merged "can we have THPs in this VMA?" logic that was previously done
    > separately by fault-path, khugepaged, and smaps "THPeligible" checks.
    >
    > During the process, the semantics of the fault path check changed in two
    > ways:
    >
    > 1) A VM_NO_KHUGEPAGED check was introduced (also added to smaps path).
    > 2) We no longer checked if non-anonymous memory had a vm_ops->huge_fault
    > handler that could satisfy the fault. Previously, this check had been
    > done in create_huge_pud() and create_huge_pmd() routines, but after
    > the changes, we never reach those routines.
    >
    > During the review of the above commits, it was determined that in-tree
    > users weren't affected by the change; most notably, since the only relevant
    > user (in terms of THP) of VM_MIXEDMAP or ->huge_fault is DAX, which is
    > explicitly approved early in approval logic. However, this was a bad
    > assumption to make as it assumes the only reason to support ->huge_fault
    > was for DAX (which is not true in general).
    >
    > Remove the VM_NO_KHUGEPAGED check when not in collapse path and give
    > any ->huge_fault handler a chance to handle the fault. Note that we
    > don't validate the file mode or mapping alignment, which is consistent
    > with the behavior before the aforementioned commits.
    >
    > Fixes: 7da4e2cb8b1f ("mm: thp: kill __transhuge_page_enabled()")
    > Reported-by: Saurabh Singh Sengar <ssengar@microsoft.com>
    > Signed-off-by: Zach O'Keefe <zokeefe@google.com>
    > Cc: Yang Shi <shy828301@gmail.com>
    > Cc: Matthew Wilcox <willy@infradead.org>
    > Cc: David Hildenbrand <david@redhat.com>
    > ---
    > I've updated the changelog to reflect discussions in [1] -- leaving
    > ack to David / Matthew on whether to take the patch.

    Works for me.

    Acked-by: David Hildenbrand <david@redhat.com>

    --
    Cheers,

    David / dhildenb

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