On Mon, Nov 25, 2013 at 03:50:11PM -0800, Andrew Morton wrote: > On Sun, 24 Nov 2013 18:38:26 -0500 Johannes Weiner <hannes@xxxxxxxxxxx> wrote: > > > ... > > > > + * Access frequency and refault distance > > + * > > + * A workload is trashing 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. > > + * > > + * In cases where the average access distance between thrashing pages > > + * is bigger than the size of memory there is nothing that can be > > + * done - the thrashing set could never fit into memory under any > > + * circumstance. > > + * > > + * However, the average access distance could be bigger than the > > + * inactive list, yet smaller than the size of memory. In this case, > > + * the set could fit into memory if it weren't for the currently > > + * active pages - which may be used more, hopefully less frequently: > > + * > > + * +-memory available to cache-+ > > + * | | > > + * +-inactive------+-active----+ > > + * a b | c d e f g h i | J K L M N | > > + * +---------------+-----------+ > > So making the inactive list smaller will worsen this problem? Only if the inactive list size is a factor in detecting repeatedly used pages. This patch series is all about removing that dependency and using non-residency information to cover that deficit a small inactive list would otherwise create. > If so, don't we have a conflict with this objective: > > > Right now we have a fixed ratio (50:50) between inactive and active > > list but we already have complaints about working sets exceeding half > > of memory being pushed out of the cache by simple streaming in the > > background. Ultimately, we want to adjust this ratio and allow for a > > much smaller inactive list. No, this IS the objective. The patches get us there by being able to detect repeated references with an arbitrary inactive list size. > > + * It is prohibitively expensive to accurately track access frequency > > + * of pages. But a reasonable approximation can be made to measure > > + * thrashing on the inactive list, after which refaulting pages can be > > + * activated optimistically to compete with the existing active pages. > > + * > > + * Approximating inactive page access frequency - Observations: > > + * > > + * 1. When a page is accesed for the first time, it is added to the > > "accessed" Whoopsa :-) Will fix that up. -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
