[PATCH] powerpc: Set a smaller value for RECLAIM_DISTANCE to enable zone reclaim

[Christoph Lameter]

On Tue, 23 Feb 2010, Anton Blanchard wrote:

> zone_reclaim_mode.txt
> Now we set zone_reclaim_mode = 1. On each iteration we continue to improve,
> but even after 10 runs of stream we have > 10% remote node memory usage.

The intend of zone reclaim was never to allocate all memory from on node.
You should not expect all memory to come from the node even if zone
reclaim works.

> reclaim_4096_pages.txt
> Instead of reclaiming 32 pages at a time, we try for a much larger batch
> of 4096. The slope is much steeper but it still takes around 6 iterations
> to get almost all local node memory.

"almost all"? How much do you want?

> wait_on_busy_flag.txt
> Here we busy wait if the ZONE_RECLAIM_LOCKED flag is set. As you suggest
> we would need to check the GFP flags etc, but so far it looks the most
> promising. We only get a few percent of remote node memory on the first
> iteration and get all local node by the second.

This would significantly impact performance. Zone reclaim should reclaim
with minimal overhead. If zone reclaim is running on another processor
then the OS already takes measures against the shortage of node local
memory. The right thing to do is to take what is currently available which
may be off node memory.
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