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

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Message-ID: <c3ff7038-a694-d311-c246-b881a2f55be7@redhat.com>
Date:   Wed, 24 Mar 2021 13:23:47 +0100
From:   David Hildenbrand <david@...hat.com>
To:     Michal Hocko <mhocko@...e.com>, Oscar Salvador <osalvador@...e.de>
Cc:     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 24.03.21 13:10, Michal Hocko wrote:
> On Wed 24-03-21 13:03:29, Michal Hocko wrote:
>> On Wed 24-03-21 11:12:59, Oscar Salvador wrote:
> [...]
> 
> an additional remark
> 
>>> - online_pages()->move_pfn_range_to_zone(): Accounts for node/zone's spanned pages
>>> - online_pages()->zone->present_pages += nr_pages;
> 
> I am pretty sure you shouldn't account vmmemmap pages to the target zone
> in some cases - e.g. vmemmap cannot be part of the movable zone, can it?
> So this would be yet another special casing. This patch has got it wrong
> unless I have missed some special casing.
> 

It's a bit unfortunate that we have to discuss the very basic design 
decisions again.

@Oscar, maybe you can share the links where we discussed all this and 
add some of it to the patch description.

I think what we have right here is good enough for an initial version, 
from where on we can improve things without having to modify calling code.

-- 
Thanks,

David / dhildenb