>>>>> "Matthew" == Matthew Dillon <[EMAIL PROTECTED]> writes:
Matthew> The primes are designed such that the page allocation Matthew> code covers *ALL* the free lists in the array, so it will Matthew> still be able to find any available free pages if its first Matthew> choice(s) are empty. Matthew> For example, prime number 3 an array size 8 will scan the Matthew> array in the following order N = (N + PRIME) & Matthew> (ARRAY_SIZE_MASK). N = (N + 3) & 7: Matthew> 0 3 6 1 4 7 2 5 ... 0 Matthew> As you can see, all the array entries are covered before Matthew> the sequence repeats. So if we want a free page in array Matthew> slot 0 but the only free pages available happen to be in Matthew> array slot 5, the above algorithm is guarenteed to find it. Matthew> Only certain prime number / power-of-2-array size Matthew> combinations have this effect, but it is very easy to write a Matthew> little program to test combinations and find the numbers best Matthew> suited to your goals. For the mathematically inclined, 3 would be a 'generator' of the group. Dave. -- ============================================================================ |David Gilbert, Velocet Communications. | Two things can only be | |Mail: [EMAIL PROTECTED] | equal if and only if they | |http://daveg.ca | are precisely opposite. | =========================================================GLO================ _______________________________________________ [EMAIL PROTECTED] mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-hackers To unsubscribe, send any mail to "[EMAIL PROTECTED]"
