On Wed, 10 Apr 2013, Wojciech Puchar wrote:
How do your tests work? Do you examine PTEs directly to check for
superpages
or are you relying on the vm.pmap.pde sysctls?
the later.
anyway - algorithm described on list - that heuristics detects consecutive
page access doesn't really help the urgent case - RANDOM access to large
amount of memory.
The algorithm is not a heuristic based on consecutive accesses, promotion
occurs when the entire superpage's worth of memory has actually been
accessed. If I remember correctly, the performance gain from superpages
was only a few percent, so spending more time trying to decide when to use
them would make the algorithm a net wash.
You should really watch the talk I linked to if you're interested, it was
quite interesting.
sequential access will get minimal improvement.
IMHO the only way that really make sens is to add options to madvise to give
kernel information about usage.
Maybe.
-Ben Kaduk
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