Re: one question about LRU mechanism

[Nikita Danilov <nikita@clusterfs.com>]

liyu@LAN writes:

[...]

 > 
 > /************************************************************/
 >         while (scan++ < nr_to_scan && !list_empty(src)) {
 >                 page = lru_to_page(src);
 >                 prefetchw_prev_lru_page(page, src, flags);
 >                                                                                                     
 >                 if (!TestClearPageLRU(page))
 >                         BUG();
 >                 list_del(&page->lru);

[...]

 > 
 > /***************************************************/
 >         while (scan++ < nr_to_scan && !list_empty(src->prev)) {

list_empty(something) and list_empty(something->prev) are equivalent for
well-formed lists.

list_empty(src) check in isolate_lru_pages() is for pathological case
when active list becomes empty. Also active and inactive lists are not
LRU, they are closer to second-chance-FIFO, it is _together_ that they
emulate LRU.

Nikita.
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