Re: [RFC 1/4] mm: create N_COHERENT_MEMORY

[Balbir Singh <bsingharora@gmail.com>]

On Thu, 2017-04-27 at 13:42 -0500, Reza Arbab wrote:
> On Wed, Apr 19, 2017 at 05:52:39PM +1000, Balbir Singh wrote:
> > In this patch we create N_COHERENT_MEMORY, which is different
> > from N_MEMORY. A node hotplugged as coherent memory will have
> > this state set. The expectation then is that this memory gets
> > onlined like regular nodes. Memory allocation from such nodes
> > occurs only when the the node is contained explicitly in the
> > mask.
> 
> Finally got around to test drive this. From what I can see, as expected,
> both kernel and userspace seem to ignore these nodes, unless you 
> allocate specifically from them. Very convenient.

Thanks for testing them!

> 
> Is "online_coherent"/MMOP_ONLINE_COHERENT the right way to trigger this?  

Now that we mark the node state at boot/hotplug time, I think we can ignore
these changes.

> That mechanism is used to specify zone, and only for a single block of 
> memory. This concept applies to the node as a whole. I think it should 
> be independent of memory onlining.
> 
> I mean, let's say online_kernel N blocks, some of them get allocated, 
> and then you online_coherent block N+1, flipping the entire node into 
> N_COHERENT_MEMORY. That doesn't seem right.
> 

Agreed, I'll remove these bits in the next posting.

Thanks for the review!
Balbir Singh.

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