Re: [PATCH] mm/spase: never partially remove memmap for early section

[Dan Williams]

On Wed, Jun 24, 2020 at 10:53 PM David Hildenbrand <david@xxxxxxxxxx> wrote:
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>
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> > Am 25.06.2020 um 01:47 schrieb Dan Williams <dan.j.williams@xxxxxxxxx>:
> >
> > ïOn Wed, Jun 24, 2020 at 3:44 PM Wei Yang
> > <richard.weiyang@xxxxxxxxxxxxxxxxx> 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.

Agree, yes, let's do the simple fix first for 5.8 and the special-case
elimination work later.