linux-kernel - Re: [PATCH v1 5/5] mm/memory_hotplug: allow to specify a default online

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Message-ID: <49764c65-842d-0446-2320-31aedb7e41cb@redhat.com>
Date:   Wed, 11 Mar 2020 16:20:35 +0100
From:   David Hildenbrand <david@...hat.com>
To:     Wei Yang <richard.weiyang@...il.com>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        linuxppc-dev@...ts.ozlabs.org, linux-hyperv@...r.kernel.org,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Michal Hocko <mhocko@...nel.org>,
        Oscar Salvador <osalvador@...e.de>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Baoquan He <bhe@...hat.com>
Subject: Re: [PATCH v1 5/5] mm/memory_hotplug: allow to specify a default
 online_type

On 11.03.20 15:26, Wei Yang wrote:
> On Wed, Mar 11, 2020 at 01:30:26PM +0100, David Hildenbrand wrote:
>> For now, distributions implement advanced udev rules to essentially
>> - Don't online any hotplugged memory (s390x)
>> - Online all memory to ZONE_NORMAL (e.g., most virt environments like
>>  hyperv)
>> - Online all memory to ZONE_MOVABLE in case the zone imbalance is taken
>>  care of (e.g., bare metal, special virt environments)
>>
>> In summary: All memory is usually onlined the same way, however, the
>> kernel always has to ask userspace to come up with the same answer.
>> E.g., HyperV always waits for a memory block to get onlined before
>> continuing, otherwise it might end up adding memory faster than
>> hotplugging it, which can result in strange OOM situations.
>>
>> Let's allow to specify a default online_type, not just "online" and
>> "offline". This allows distributions to configure the default online_type
>> when booting up and be done with it.
>>
>> We can now specify "offline", "online", "online_movable" and
>> "online_kernel" via
>> - "memhp_default_state=" on the kernel cmdline
>> - /sys/devices/systemn/memory/auto_online_blocks
>> just like we are able to specify for a single memory block via
>> /sys/devices/systemn/memory/memoryX/state
>>
>> Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
>> Cc: Andrew Morton <akpm@...ux-foundation.org>
>> Cc: Michal Hocko <mhocko@...nel.org>
>> Cc: Oscar Salvador <osalvador@...e.de>
>> Cc: "Rafael J. Wysocki" <rafael@...nel.org>
>> Cc: Baoquan He <bhe@...hat.com>
>> Cc: Wei Yang <richard.weiyang@...il.com>
>> Signed-off-by: David Hildenbrand <david@...hat.com>
> 
> Ok, I got the reason to leave the change on string compare here.

Thanks for your *very fast* review! :)


-- 
Thanks,

David / dhildenb