Re: [PATCH v5 01/14] memory-hotplug: try to offline the memory twiceto avoid dependence

[Tang Chen]

Hi Glauber,

On 01/09/2013 11:09 PM, Glauber Costa wrote:
> > We try to make all page_cgroup allocations local to the node they are describing
> > now. If the memory is the first memory onlined in this node, we will allocate
> > it from the other node.
> >
> > For example, node1 has 4 memory blocks: 8-11, and we online it from 8 to 11
> > 1. memory block 8, page_cgroup allocations are in the other nodes
> > 2. memory block 9, page_cgroup allocations are in memory block 8
> >
> > So we should offline memory block 9 first. But we don't know in which order
> > the user online the memory block.
> >
> > I think we can modify memcg like this:
> > allocate the memory from the memory block they are describing
> >
> > I am not sure it is OK to do so.
>
> I don't see a reason why not.

I'm not sure, but if we do this, we could bring in a fragment for each
memory block (a memory section, 128MB, right?). Is this a problem when
we use large page (such as 1GB page) ?

Even if not, will these fragments make any bad effects ?

Thank. :)

> You would have to tweak a bit the lookup function for page_cgroup, but
> assuming you will always have the pfns and limits, it should be easy to do.
>
> I think the only tricky part is that today we have a single
> node_page_cgroup, and we would of course have to have one per memory
> block. My assumption is that the number of memory blocks is limited and
> likely not very big. So even a static array would do.
>
> Kamezawa, do you have any input in here?

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