On Wed, Jul 16, 2014 at 01:53:55AM +0000, Zhang, Tianfei wrote: > Hi Johannes, > > May I ask you a question about refault distance? > > Is it supposed the distance of the first and second time to access the a faulted page cache is the same? In reality how about the > ratio will be the same? > > Refault Distance1 = Refault Distance2 > > On the first refault, We supposed that: > Refault Distance = A > NR_INACTIVE_FILE = B > NR_ACTIVE_FILE = C > > * fault page add to inactive list tail > The Refault Distance = A > | > * B | | C > * +--------------+ | +-------------+ > * reclaim <- | inactive | <-+-- demotion | active | <--+ > * +--------------+ +-------------+ | > * | | > * +-------------- promotion ------------------+ > > > Why we use A <= C to add faulted page to ACTIVE LIST? > > Your patch is want to solve "A workload is thrashing when its pages are frequently used > but they are evicted from the inactive list every time before another access would have > promoted them to the active list." ? > > so when a First Refault page add to INACTIVE LIST, it is a Distance B before eviction. > So I am confuse the condition on workingset_refault(). The reuse distance of a page is B + A. B + C is the available memory overall. When a page refaults, we want to compare its reuse distance to overall memory to see if it is eligible for activation (= accessed twice while in memory). That check would be A + B <= B + C. But we can simply drop B on both sides and get A <= C. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>