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Subject: Re: [PATCH v6 2/8] mm,memory_hotplug: Relax fully spanned sections
 check
To:     Oscar Salvador <osalvador@suse.de>
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
References: <df9bdb5157d6ad2f4a922d396ddf0c07@suse.de>
 <59A04B1D-08D6-4E71-A382-F5503A6E0AF7@redhat.com>
 <20210407074249.GA9353@linux>
From:   David Hildenbrand <david@redhat.com>
Organization: Red Hat GmbH
Message-ID: <f23128b1-0d27-76f0-10b2-7816092089ac@redhat.com>
Date:   Wed, 7 Apr 2021 09:43:43 +0200
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On 07.04.21 09:42, Oscar Salvador wrote:
> On Tue, Apr 06, 2021 at 10:43:01PM +0200, David Hildenbrand wrote:
>> But not end_pfn as given in my version or what am I missing?
> 
> Nah, was my fault, I managed to see:
> 
>   if (WARN_ON_ONCE(!nr_pages ||
>           !IS_ALIGNED(start_pfn, pageblock_nr_pages))
>           !IS_ALIGNED(start_pfn | nr_pages, PAGES_PER_SECTION)))
> 
> which would not work.
> 
> I agree that keeping the PAGES_PER_SECTION check maks this safer, so this all
> should have been:
> 
> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> index 0cdbbfbc5757..25e59d5dc13c 100644
> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -838,9 +838,14 @@ int __ref online_pages(unsigned long pfn, unsigned long nr_pages,
>          int ret;
>          struct memory_notify arg;
>   
> -       /* We can only online full sections (e.g., SECTION_IS_ONLINE) */
> +       /* We can only offline full sections (e.g., SECTION_IS_ONLINE).
> +        * However, when using e.g: memmap_on_memory, some pages are initialized
> +        * prior to calling in here. The remaining amount of pages must be
> +        * pageblock aligned.
> +        */
>          if (WARN_ON_ONCE(!nr_pages ||
> -                        !IS_ALIGNED(pfn | nr_pages, PAGES_PER_SECTION)))
> +                        !IS_ALIGNED(pfn, pageblock_nr_pages) ||
> +                        !IS_ALIGNED(pfn + nr_pages, PAGES_PER_SECTION)))
>                  return -EINVAL;
>   
>          mem_hotplug_begin();
> @@ -1573,9 +1578,14 @@ int __ref offline_pages(unsigned long start_pfn, unsigned long nr_pages)
>          int ret, node;
>          char *reason;
>   
> -       /* We can only offline full sections (e.g., SECTION_IS_ONLINE) */
> +       /* We can only offline full sections (e.g., SECTION_IS_ONLINE).
> +        * However, when using e.g: memmap_on_memory, some pages are initialized
> +        * prior to calling in here. The remaining amount of pages must be
> +        * pageblock aligned.
> +        */
>          if (WARN_ON_ONCE(!nr_pages ||
> -                        !IS_ALIGNED(start_pfn | nr_pages, PAGES_PER_SECTION)))
> +                        !IS_ALIGNED(start_pfn, pageblock_nr_pages) ||
> +                        !IS_ALIGNED(start_pfn + nr_pages, PAGES_PER_SECTION)))
>                  return -EINVAL;
>   
>          mem_hotplug_begin();
> 
>   
> 

Reviewed-by: David Hildenbrand <david@redhat.com>

-- 
Thanks,

David / dhildenb