From: Johannes Weiner <hannes@xxxxxxxxxxx> Subject: mm: vmscan: limit the range of LRU type balancing When LRU cost only shows up on one list, we abruptly stop scanning that list altogether. That's an extreme reaction: by the time the other list starts thrashing and the pendulum swings back, we may have no recent age information on the first list anymore, and we could have significant latencies until the scanner has caught up. Soften this change in the feedback system by ensuring that no list receives less than a third of overall pressure, and only distribute the other 66% according to LRU cost. This ensures that we maintain a minimum rate of aging on the entire workingset while it's being pressured, while still allowing a generous rate of convergence when the relative sizes of the lists need to adjust. Link: http://lkml.kernel.org/r/20200520232525.798933-15-hannes@xxxxxxxxxxx Signed-off-by: Johannes Weiner <hannes@xxxxxxxxxxx> Cc: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx> Cc: Michal Hocko <mhocko@xxxxxxxx> Cc: Minchan Kim <minchan@xxxxxxxxxx> Cc: Rik van Riel <riel@xxxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- mm/vmscan.c | 22 +++++++++++++--------- 1 file changed, 13 insertions(+), 9 deletions(-) --- a/mm/vmscan.c~mm-vmscan-limit-the-range-of-lru-type-balancing +++ a/mm/vmscan.c @@ -2237,12 +2237,11 @@ static void get_scan_count(struct lruvec unsigned long *nr) { struct mem_cgroup *memcg = lruvec_memcg(lruvec); + unsigned long anon_cost, file_cost, total_cost; int swappiness = mem_cgroup_swappiness(memcg); u64 fraction[2]; u64 denominator = 0; /* gcc */ - unsigned long anon_prio, file_prio; enum scan_balance scan_balance; - unsigned long totalcost; unsigned long ap, fp; enum lru_list lru; @@ -2301,17 +2300,22 @@ static void get_scan_count(struct lruvec * the relative IO cost of bringing back a swapped out * anonymous page vs reloading a filesystem page (swappiness). * + * Although we limit that influence to ensure no list gets + * left behind completely: at least a third of the pressure is + * applied, before swappiness. + * * With swappiness at 100, anon and file have equal IO cost. */ - anon_prio = swappiness; - file_prio = 200 - anon_prio; + total_cost = sc->anon_cost + sc->file_cost; + anon_cost = total_cost + sc->anon_cost; + file_cost = total_cost + sc->file_cost; + total_cost = anon_cost + file_cost; - totalcost = sc->anon_cost + sc->file_cost; - ap = anon_prio * (totalcost + 1); - ap /= sc->anon_cost + 1; + ap = swappiness * (total_cost + 1); + ap /= anon_cost + 1; - fp = file_prio * (totalcost + 1); - fp /= sc->file_cost + 1; + fp = (200 - swappiness) * (total_cost + 1); + fp /= file_cost + 1; fraction[0] = ap; fraction[1] = fp; _
