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From:   Dan Williams <dan.j.williams@intel.com>
Date:   Wed, 24 Jun 2020 16:47:17 -0700
Message-ID: <CAPcyv4gMQsBSQ-kXM6H_zz96ZTJ5F0XnDfq6_mZTn4t9JwmEpA@mail.gmail.com>
Subject: Re: [PATCH] mm/spase: never partially remove memmap for early section
To:     Wei Yang <richard.weiyang@linux.alibaba.com>
Cc:     Michal Hocko <mhocko@kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Oscar Salvador <osalvador@suse.de>,
        Linux MM <linux-mm@kvack.org>, Baoquan He <bhe@redhat.com>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        David Hildenbrand <david@redhat.com>
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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.