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

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Message-Id: <4D73CD59-BFD5-401A-A001-41F7BF5641BA@redhat.com>
Date:   Thu, 25 Jun 2020 07:53:37 +0200
From:   David Hildenbrand <david@...hat.com>
To:     Dan Williams <dan.j.williams@...el.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>,
        David Hildenbrand <david@...hat.com>
Subject: Re: [PATCH] mm/spase: never partially remove memmap for early section



> 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.

At least my ack stands.