Re: [PATCH] Optimize out pte_chain take three

William Lee Irwin III
2002-07-11T22:54:08Z

On Thu, Jul 11, 2002 at 12:54:12PM -0700, Andrew Morton wrote:
> The problem is the access pattern. It shouldn't be random-uniform.
> But what should it be? random-gaussian?
> So: map a large file, access it random-gaussian. malloc some memory,
> access it random-gaussian. Apply eviction pressure. Measure throughput.
> Optimise throughput.
> Does this not capture what the VM is supposed to do?
> What workload is rmap supposed to be good at?

I wouldn't go through the trouble of Guassian, a step distribution,
i.e. sets A and B with P(A) = p < q = P(B), and "effective detection
of the working set" is seeing how much of the working set was retained
instead of reclaimed as p -> m(A)/m(A U B) and how much determining it
cost in terms of cpu. Or that's my first impression. The distributions
P(. | A) and P(. | B) don't matter aside from the probabilities of the
whole of A and B themselves and non-uniform creates harder to analyze
things as bits of A may well be less likely than bits of B so making
P(. | A) and P(. | B) uniform sounds easiest to me.

Throughput is probably easy to disturb in unrelated ways, but (of course)
necessary to keep track of.

Cheers,
Bill