Nick Piggin writes:
> PG_lru is protected by zone->lru_lock. It does not need TestSet/TestClear
> operations.
>
> Signed-off-by: Nick Piggin <[email protected]>
>
> Index: linux-2.6/mm/vmscan.c
> ===================================================================
> --- linux-2.6.orig/mm/vmscan.c
> +++ linux-2.6/mm/vmscan.c
> @@ -775,9 +775,10 @@ int isolate_lru_page(struct page *page)
> if (PageLRU(page)) {
> struct zone *zone = page_zone(page);
> spin_lock_irq(&zone->lru_lock);
> - if (TestClearPageLRU(page)) {
> + if (PageLRU(page)) {
> ret = 1;
> get_page(page);
> + ClearPageLRU(page);
Why is that better? ClearPageLRU() is also "atomic" operation (in the
sense of using LOCK_PREFIX on x86), so it seems this change strictly
adds cycles to the hot-path when page is on LRU.
Nikita.
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