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o Limit the size of the region ID map to 64KB. This gives a bitmap that is large enough to keep track of 2^19 numbers. The minimal map size is 32KB. The reason we limit the map size is that processor models may have implemented a 24-bit region ID, which would give a 2MB bitmap while the maximum number of allocations is always less than PID_MAX*5, which is less than 2^19. o Allocate all region IDs up-front. The slight downside of reserving more RIDs then a process needs (3 for ia64 native and 1 for ia32) is preferable over the call to pmap_ensure_rid() where RIDs are allocated on demand. On SMP systems this may lead to a race condition. o When allocating a region ID, don't use arc4random(). We're not interested in randomness or uniform distribution across the spectrum. We only need uniqueness. Random numbers may easily collide when the number of allocated RIDs is high, creating a possibly unbounded retry rate.
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