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

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Message-ID: <20200625222940.GA16822@L-31X9LVDL-1304.local>
Date:   Fri, 26 Jun 2020 06:29:40 +0800
From:   Wei Yang <richard.weiyang@...ux.alibaba.com>
To:     Dan Williams <dan.j.williams@...el.com>
Cc:     David Hildenbrand <david@...hat.com>,
        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 Thu, Jun 25, 2020 at 12:46:43PM -0700, Dan Williams wrote:
>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.

Ok, let me send v2 with detailed change log and a comment in code first.

Thanks all for your time.

-- 
Wei Yang
Help you, Help me