On Thu, Jan 19, 2006 at 08:48:52PM +0300, Nikita Danilov wrote:
> 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.
>
Less restrictive memory ordering requirements.
Nick
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