linux-kernel - Re: [PATCH] mm, sparse: fix typo in online_mem

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Message-Id: <d687658d-088c-f1c7-77f9-d0b5845e24c5@linux.vnet.ibm.com>
Date:   Tue, 5 Sep 2017 14:14:38 +0530
From:   Anshuman Khandual <khandual@...ux.vnet.ibm.com>
To:     Michal Hocko <mhocko@...nel.org>,
        Anshuman Khandual <khandual@...ux.vnet.ibm.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Vlastimil Babka <vbabka@...e.cz>, linux-mm@...ck.org,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] mm, sparse: fix typo in online_mem_sections

On 09/05/2017 01:07 PM, Michal Hocko wrote:
> On Tue 05-09-17 09:28:36, Michal Hocko wrote:
>> On Tue 05-09-17 12:32:28, Anshuman Khandual wrote:
>>> On 09/04/2017 04:52 PM, Michal Hocko wrote:
>>>> From: Michal Hocko <mhocko@...e.com>
>>>>
>>>> online_mem_sections accidentally marks online only the first section in
>>>> the given range. This is a typo which hasn't been noticed because I
>>>> haven't tested large 2GB blocks previously. All users of
>>>
>>> Section sizes are normally less than 2GB. Could you please elaborate
>>> why this never got noticed before ?
>>
>> Section size is 128MB which is the default block size as well. So we
>> have one section per block. But if the amount of memory is very large
>> (64GB - see probe_memory_block_size) then we have a 2GB memory blocks
>> so multiple sections per block.
> 
> And just to clarify. Not that 64G would be too large but the original
> patch has been merged in 4.13 so nobody probably managed to hit that
> _yet_.

Got it. Section size is 16MB and block size is 256MB on most of the
POWER platforms. Hence this could have affected them as well.