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    SubjectRe: [PATCH] mm/spase: never partially remove memmap for early section
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    > Am 26.06.2020 um 00:40 schrieb Wei Yang <richard.weiyang@linux.alibaba.com>:
    >
    > On Thu, Jun 25, 2020 at 07:53:37AM +0200, David Hildenbrand wrote:
    >>
    >>
    >>>> Am 25.06.2020 um 01:47 schrieb Dan Williams <dan.j.williams@intel.com>:
    >>>
    >>> On Wed, Jun 24, 2020 at 3:44 PM Wei Yang
    >>> <richard.weiyang@linux.alibaba.com> wrote:
    >>> [..]
    >>>>> So, you are right that there is a mismatch here, but I think the
    >>>>> comprehensive fix is to allow early sections to be partially
    >>>>> depopulated/repopulated rather than have section_activate() and
    >>>>> section_deacticate() special case early sections. The special casing
    >>>>> is problematic in retrospect as section_deactivate() can't be
    >>>>> maintained without understand special rules in section_activate().
    >>>>
    >>>> Hmm... This means we need to adjust pfn_valid() too, which always return true
    >>>> for early sections.
    >>>
    >>> Right, rather than carry workarounds in 3 locations, and the bug that
    >>> has resulted from then getting out of sync, just teach early section
    >>> mapping to allow for the subsection populate/depopulate.
    >>>
    >>
    >> I prefer the easy fix first - IOW what we Here here. Especially, pfn_to_online_page() will need changes as well.
    >>
    >
    > Hi, David,
    >
    > Which part of pfn_to_online_page() needs to be changed? pfn_valid_within()
    > would call pfn_valid() to check the pfn first. This looks enough for me.

    Not for all configurations. For some (e.g., x86 iirc) it‘s just a nop.
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