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

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Message-ID: <CAPcyv4hnsUoavnzX8q5VReiLXrOsOYW0Ef5GDKxQtS+6pQLy4A@mail.gmail.com>
Date:   Thu, 25 Jun 2020 12:46:43 -0700
From:   Dan Williams <dan.j.williams@...el.com>
To:     David Hildenbrand <david@...hat.com>
Cc:     Wei Yang <richard.weiyang@...ux.alibaba.com>,
        Michal Hocko <mhocko@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Oscar Salvador <osalvador@...e.de>,
        Linux MM <linux-mm@...ck.org>, Baoquan He <bhe@...hat.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] mm/spase: never partially remove memmap for early section

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

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