Re: NUMA node swapping V3

["Martin J. Bligh" <mbligh@aracnet.com>]

> Changes from V2: better documentation, fix missing #ifdef
> 
> In a NUMA systems single nodes may run out of memory. This may occur even
> by only reading from files which will clutter node memory with cached
> pages from the file.
> 
> However, as long as the system as a whole does have enough memory
> available, kswapd is not run at all. This means that a process allocating
> memory and running on a node that has no memory left, will get memory
> allocated from other nodes which is inefficient to handle. It would be
> better if kswapd would throw out some pages (maybe some of the cached
> pages from files that have only once been read) to reclaim memory in the
> node.
> 
> The following patch checks the memory usage after each allocation in a
> zone. If the allocation in a zone falls below a certain minimum, kswapd is
> started for that zone alone.
> 
> The minimum may be controlled through /proc/sys/vm/node_swap which is set
> to zero by default and thus is off.
> 
> If it is set for example to 100 then kswapd will be run on
> a zone/node if less than 10% of pages are available after an allocation.

I thought even the SGI people were saying this wouldn't actually help you,
due to some workload issues?

M.

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