Re: Zoned CART

[Christoph Lameter <clameter@engr.sgi.com>]

Hmm. I am a bit concerned about the proliferation of counters in CART 
because these may lead to bouncing cachelines.

The paper mentions some relationships between the different values. 

If we had a counter for the number of pages resident (nr_rpages) 
(|T1|+|T2|) then that counter would gradually approach c and then no 
longer change.

Then

|T2| = nr_rpages - |T1|

Similarly if we had a counter for the number of pages on the evicted 
list (nr_evicted) then that counter would also gradually approach c and 
then stay constant. nr_evicted would only increase if nr_rpages has 
already reached c which is another good thing to avoid bouncing 
cachelines.

Then also

|B2| = nr_evicted - |B1|

Thus we could reduce the frequency of counter increments on a fully 
loaded system (where nr_rpages = c and nr_eviced = c) by 
calculating some variables:

#define nr_inactive (nr_rpages - nr_active)
#define nr_evicted_longterm (nr_evicted - nr_evicted_shortterm)

There is also a relationship between |S| and |L| since these attributes 
are only used on resident pages.

|L| = nr_rpages - |S|

So

#define nr_longterm (nr_rpages - nr_shortterm)

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