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Subject: Re: [PATCH 02/10] mm/numa: automatically generate node migration
 order
To:     Oscar Salvador <osalvador@suse.de>, Wei Xu <weixugc@google.com>
Cc:     Dave Hansen <dave.hansen@linux.intel.com>,
        Linux MM <linux-mm@kvack.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Yang Shi <shy828301@gmail.com>,
        David Rientjes <rientjes@google.com>,
        Huang Ying <ying.huang@intel.com>,
        Dan Williams <dan.j.williams@intel.com>
References: <20210401183216.443C4443@viggo.jf.intel.com>
 <20210401183219.DC1928FA@viggo.jf.intel.com>
 <CAAPL-u8Jk-i-9-iSnU7_nb-k2ZMqdRk5c88d-M6Bi1rfv4kSLQ@mail.gmail.com>
 <20210414080849.GA20886@linux>
From:   David Hildenbrand <david@redhat.com>
Organization: Red Hat
Message-ID: <926bd5f9-bf05-2e01-26da-da3f66439d3b@redhat.com>
Date:   Wed, 14 Apr 2021 10:12:29 +0200
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On 14.04.21 10:08, Oscar Salvador wrote:
> On Fri, Apr 09, 2021 at 08:07:08PM -0700, Wei Xu wrote:
>> On Thu, Apr 1, 2021 at 11:35 AM Dave Hansen <dave.hansen@linux.intel.com> wrote:
>>> + * When Node 0 fills up, its memory should be migrated to
>>> + * Node 1.  When Node 1 fills up, it should be migrated to
>>> + * Node 2.  The migration path start on the nodes with the
>>> + * processors (since allocations default to this node) and
>>> + * fast memory, progress through medium and end with the
>>> + * slow memory:
>>> + *
>>> + *     0 -> 1 -> 2 -> stop
>>> + *     3 -> 4 -> 5 -> stop
>>> + *
>>> + * This is represented in the node_demotion[] like this:
>>> + *
>>> + *     {  1, // Node 0 migrates to 1
>>> + *        2, // Node 1 migrates to 2
>>> + *       -1, // Node 2 does not migrate
>>> + *        4, // Node 3 migrates to 4
>>> + *        5, // Node 4 migrates to 5
>>> + *       -1} // Node 5 does not migrate
>>> + */
>>
>> In this example, if we want to support multiple nodes as the demotion
>> target of a source node, we can group these nodes into three tiers
>> (classes):
>>
>> fast class:
>> 0 -> {1, 4}  // 1 is the preferred
>> 3 -> {4, 1}  // 4 is the preferred
>>
>> medium class:
>> 1 -> {2, 5}  // 2 is the preferred
>> 4 -> {5, 2}  // 5 is the preferred
>>
>> slow class:
>> 2 -> stop
>> 5 -> stop
> 
> Hi Wei Xu,
> 
> I have some questions about it
> 
> Fast class/memory are pictured as those nodes with CPUs, while Slow class/memory
> are PMEM, right?
> Then, what stands for medium class/memory?

My guest best is that fast class is something like HBM (High Bandwidth 
Memory), medium class is ordinary RAM, slow class is PMEM.

-- 
Thanks,

David / dhildenb