Messages in this thread | | | From | Nikita Danilov <> | Date | Sun, 4 Dec 2005 15:11:28 +0300 | Subject | Re: [PATCH 01/16] mm: delayed page activation |
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Wu Fengguang writes: > When a page is referenced the second time in inactive_list, mark it with > PG_activate instead of moving it into active_list immediately. The actual > moving work is delayed to vmscan time. > > This implies two essential changes: > - keeps the adjecency of pages in lru;
But this change destroys LRU ordering: at the time when shrink_list() inspects PG_activate bit, information about order in which mark_page_accessed() was called against pages is lost. E.g., suppose inactive list initially contained pages
/* head */ (P1, P2, P3) /* tail */
all of them referenced. Then mark_page_accessed(), is called against P1, P2, and P3 (in that order). With the old code active list would end up
/* head */ (P3, P2, P1) /* tail */
which corresponds to LRU. With delayed page activation, pages are moved to head of the active list in the order they are analyzed by shrink_list(), which gives
/* head */ (P1, P2, P3) /* tail */
on the active list, that is _inverse_ LRU order.
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