linux-kernel - Re: [PATCH v1] drivers/base/node.c: Simplify unregister_memory_block_under

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Message-ID: <c203ae99-e47f-a7dd-83f0-93196125db70@redhat.com>
Date:   Fri, 19 Jul 2019 13:42:07 +0200
From:   David Hildenbrand <david@...hat.com>
To:     Michal Hocko <mhocko@...nel.org>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Stephen Rothwell <sfr@...b.auug.org.au>,
        Pavel Tatashin <pasha.tatashin@...een.com>,
        Oscar Salvador <osalvador@...e.de>
Subject: Re: [PATCH v1] drivers/base/node.c: Simplify
 unregister_memory_block_under_nodes()

On 19.07.19 13:36, Michal Hocko wrote:
> On Fri 19-07-19 11:20:43, David Hildenbrand wrote:
>> On 19.07.19 11:13, Michal Hocko wrote:
>>> On Fri 19-07-19 11:05:51, David Hildenbrand wrote:
>>>> On 19.07.19 10:42, Michal Hocko wrote:
>>>>> On Thu 18-07-19 16:22:39, David Hildenbrand wrote:
>>>>>> We don't allow to offline memory block devices that belong to multiple
>>>>>> numa nodes. Therefore, such devices can never get removed. It is
>>>>>> sufficient to process a single node when removing the memory block.
>>>>>>
>>>>>> Remember for each memory block if it belongs to no, a single, or mixed
>>>>>> nodes, so we can use that information to skip unregistering or print a
>>>>>> warning (essentially a safety net to catch BUGs).
>>>>>
>>>>> I do not really like NUMA_NO_NODE - 1 thing. This is yet another invalid
>>>>> node that is magic. Why should we even care? In other words why is this
>>>>> patch an improvement?
>>>>
>>>> Oh, and to answer that part of the question:
>>>>
>>>> We no longer have to iterate over each pfn of a memory block to be removed.
>>>
>>> Is it possible that we are overzealous when unregistering syfs files and
>>> we should simply skip the pfn walk even without this change?
>>>
>>
>> I assume you mean something like v1 without the warning/"NUMA_NO_NODE -1"?
>>
>> See what I have right now below.
> 
> Yes. I didn'g get to look closely but you caught the idea. Thanks!
> 

Will do a quick test and resent later this day, thanks for having a look!

-- 

Thanks,

David / dhildenb