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Date:   Tue, 06 Apr 2021 18:33:59 +0200
From:   Oscar Salvador <osalvador@suse.de>
To:     David Hildenbrand <david@redhat.com>
Cc:     Andrew Morton <akpm@linux-foundation.org>,
        Michal Hocko <mhocko@kernel.org>,
        Anshuman Khandual <anshuman.khandual@arm.com>,
        Pavel Tatashin <pasha.tatashin@soleen.com>,
        Vlastimil Babka <vbabka@suse.cz>, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH v6 2/8] mm,memory_hotplug: Relax fully spanned sections
 check
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On 2021-04-06 17:32, David Hildenbrand wrote:
> I'd only relax start_pfn. That way the function is pretty much
> impossible to abuse for sub-section onlining/offlining.
> 
> if (WARN_ON_ONCE(!nr_pages ||
> 		 !IS_ALIGNED(start_pfn, pageblock_nr_pages))
> 		 !IS_ALIGNED(start_pfn + nr_pages, PAGES_PER_SECTION)))

But this is not going to work.
When using memmap_on_memory, the nr of pages that online_pages() and 
offline_pages() get might be less than PAGES_PER_SECTION, so this check 
will always blow us up.

-- 
Oscar Salvador
SUSE L3