linux-kernel - Re: [PATCH v5 1/5] mm,memory_hotplug: Allocate memmap from the added memory range

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Message-ID: <92fe19d0-56ac-e929-a9c1-d6a4e0da39d1@redhat.com>
Date:   Thu, 25 Mar 2021 17:20:23 +0100
From:   David Hildenbrand <david@...hat.com>
To:     Michal Hocko <mhocko@...e.com>
Cc:     Oscar Salvador <osalvador@...e.de>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Anshuman Khandual <anshuman.khandual@....com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Pavel Tatashin <pasha.tatashin@...een.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v5 1/5] mm,memory_hotplug: Allocate memmap from the added
 memory range

On 25.03.21 17:07, Michal Hocko wrote:
> On Thu 25-03-21 16:35:58, Michal Hocko wrote:
> [...]
>> So there is indeed a difference. One way around that would be to mark
>> vmemmap pages (e.g. PageReserved && magic value stored somewhere in the
>> struct page - resembling bootmem vmemmaps) or mark section fully backing
>> vmemmaps as online (ugly).
> 
> I am not yet ready to give up on this. Here is a quick stab at the
> pfn_to_online_page approach. It is not great but it is not really
> terrible either. I think we can do better and skip

We both seem to have a different taste, to phrase it in a nice way :) ; 
but well, you seem to have set your mind (just like I seem to have set 
mine when trying to find a nice and somewhat-clean way to handle this 
when discussing it in the past).

I expressed my opinion, shared my findings and expressed my concerns; 
the series has my RB and the discussion here is around something I 
consider in no way better than what we have right now. I'll let Oscar 
handle discussing this topic further (sorry Oscar! :) ), but I'll 
happily review what the outcome of that will be.

-- 
Thanks,

David / dhildenb