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Message-ID: <a9ca9b75-1410-445f-9e73-2db02acff1ed@redhat.com>
Date:   Thu, 16 Nov 2023 20:23:35 +0100
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Subject: Re: [PATCH 6/8] s390/mm: implement MEM_PHYS_ONLINE MEM_PHYS_OFFLINE
 memory notifiers
Content-Language: en-US
From:   David Hildenbrand <david@redhat.com>
To:     Sumanth Korikkar <sumanthk@linux.ibm.com>
Cc:     linux-mm <linux-mm@kvack.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Oscar Salvador <osalvador@suse.de>,
        Michal Hocko <mhocko@suse.com>,
        "Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com>,
        Anshuman Khandual <anshuman.khandual@arm.com>,
        Gerald Schaefer <gerald.schaefer@linux.ibm.com>,
        Alexander Gordeev <agordeev@linux.ibm.com>,
        Heiko Carstens <hca@linux.ibm.com>,
        Vasily Gorbik <gor@linux.ibm.com>,
        linux-s390 <linux-s390@vger.kernel.org>,
        LKML <linux-kernel@vger.kernel.org>
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>>>
>>> Maybe s390x should just provide a dedicate interface to add these memory
>>> blocks instead of adding them during boot and then relying on the old way of
>>> using online/offline set them online/offline.
>>
>> Existing behavior:
>> The current 'lsmem -a' command displays both online and standby memory.
>>
>> interface changes:
>> If a new interface is introduced and standby memory is no longer listed,
>> the following consequences might occur:
>>
>> 1. Running 'lsmem -a' would only show online memory, potentially leading
>>      to user complaints.
> 
> That's why the new, clean way of doing it will require a world switch.
> If the admin wants the benefits of altmap/memmap allocation, it can be
> enabled.

BTW, thinking about it, I guess one could teach lsmem (and maybe chmem) 
to consult additional interfaces on s390x to show standby memory that's 
not added to the system yet.

-- 
Cheers,

David / dhildenb