a very occasional diary.

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2005-04-05

page tickets


MACH VM had (or still has if Mac OS X counts) an interesting detail in its VM scanner implementation:
osfmk/vm/vm_page.h
/*
 * Each page entered on the inactive queue obtains a ticket from a
 * particular ticket roll. Pages granted tickets from a particular
 * roll generally flow through the queue as a group. In this way when a
 * page with a ticket from a particular roll is pulled from the top of the
 * queue it is extremely likely that the pages near the top will have tickets
 * from the same or adjacent rolls. In this way the proximity to the top
 * of the queue can be loosely ascertained by determining the identity of
 * the roll the pages ticket came from.
 */
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