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

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Message-Id: <580EB3CB.5080200@linux.vnet.ibm.com>
Date:   Tue, 25 Oct 2016 06:52:19 +0530
From:   Anshuman Khandual <khandual@...ux.vnet.ibm.com>
To:     Dave Hansen <dave.hansen@...el.com>,
        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 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.