linux-kernel - Re: [RFC 1/8] mm: Define coherent device memory node

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Date:   Tue, 25 Oct 2016 08:47:01 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     Anshuman Khandual <khandual@...ux.vnet.ibm.com>,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org
Cc:     mhocko@...e.com, js1304@...il.com, vbabka@...e.cz, mgorman@...e.de,
        minchan@...nel.org, akpm@...ux-foundation.org,
        aneesh.kumar@...ux.vnet.ibm.com, bsingharora@...il.com
Subject: Re: [RFC 1/8] mm: Define coherent device memory node

On 10/24/2016 06:22 PM, Anshuman Khandual wrote:
> On 10/24/2016 10:39 PM, Dave Hansen wrote:
>>> +#ifdef CONFIG_COHERENT_DEVICE
>>>> +#define node_cdm(nid)          (NODE_DATA(nid)->coherent_device)
>>>> +#define set_cdm_isolation(nid) (node_cdm(nid) = 1)
>>>> +#define clr_cdm_isolation(nid) (node_cdm(nid) = 0)
>>>> +#define isolated_cdm_node(nid) (node_cdm(nid) == 1)
>>>> +#else
>>>> +#define set_cdm_isolation(nid) ()
>>>> +#define clr_cdm_isolation(nid) ()
>>>> +#define isolated_cdm_node(nid) (0)
>>>> +#endif
>> FWIW, I think adding all this "cdm" gunk in the names is probably a bad
>> thing.
>>
>> I can think of other memory types that are coherent, but
>> non-device-based that might want behavior like this.
> 
> Hmm, I was not aware about non-device-based coherent memory. Could you
> please name some of them ? If thats the case we need to change CDM to
> some thing which can accommodate both device and non device based
> coherent memory. May be like "Differentiated/special coherent memory".
> But it needs to communicate that its not system RAM. Thats the idea.

Intel has some stuff called MCDRAM.  It's described in detail here:

> https://software.intel.com/en-us/articles/mcdram-high-bandwidth-memory-on-knights-landing-analysis-methods-tools

You can also Google around for more information.

I believe Samsung has a technology called High Bandwidth Memory (HBM)
that's already a couple of generations old that sounds similar.