Re: [PATCH] GFP_THISNODE for the slab allocator

[Paul Jackson <pj@sgi.com>]

Andrew wrote:
> Why is it not sufficient to cache the most-recent zone*  in task_struct?

Because ...

pj - quoting himself:
> Just one current_allocation_zone would not be enough.  Each node that
> the cpuset allowed would require its own current_allocation_zone.  For
> example, on a big honkin NUMA box with 2 CPUs per Node, tasks running
> on CPU 32, Node 16, might be able to find free memory right on that
> Node 16.  But another task in the same cpuset running on CPU 112, Node
> 56 might have to scan past a dozen Nodes to Node 68 to find memory.

Extending the above example, the task on CPU 32 and the one on CPU
112 could be the same task, running in the same cpuset the whole time,
after being rescheduled from one CPU to another.  The task would need
not one cached most-recent zone*, but one for each node it might find
itself on.

I'm pretty sure you don't want to put MAX_NUMNODES 'struct zone'
pointers in each task struct.

-- 
                  I won't rest till it's the best ...
                  Programmer, Linux Scalability
                  Paul Jackson <pj@sgi.com> 1.925.600.0401

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