On Mon, 6 Nov 2006 12:58:52 -0800 (PST)
Christoph Lameter <[email protected]> wrote:
> > OK, but if two nodes have a lot of free pages and the rest don't then
> > interleave will consume those free pages without performing any reclaim
> > from all the other nodes. Hence hostpots or imbalances.
> >
> > Whatever they are. Why does it matter?
>
> Hotspots create lots of requests going to the same numa node. The nodes
> have a limited capability to service cacheline requests and the bandwidth
> on the interlink is also limited. If too many processors request
> information from the same remote node then performance will drop.
OK.
> There are different kind of data in a NUMA system:
>
> Data that is node local is only accessed by the local processor. For node
> local data we have no such concerns since the interlink is not used. Quite
> a lot of kernel data per node or per cpu and thus is not a problem.
>
> For shared data that is known to be performance critical--and where we
> know that the data is accessed from multiple nodes--there we need to
> balance the data between multiple nodes to avoid overloads and
> to keep the system running at optimal speed. That is where interleave
> becomes important.
But doesn't this patch introduce considerable risks of the above problems
occurring? In the two-nodes-have-lots-of-free-memory scenario?
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