On 08/17/2012 07:34 PM, Ying Han wrote:
On Thu, Aug 16, 2012 at 8:37 AM, Rik van Riel <riel@xxxxxxxxxx> wrote:
+ /* + * Reclaim from the top scoring lruvec until we freed enough + * pages, or its reclaim priority has halved. + */ + do { + shrink_lruvec(victim_lruvec, sc); + score = reclaim_score(memcg, victim_lruvec); + } while (sc->nr_to_reclaim > 0 && score > max_score / 2);This would violate the user expectation of soft_limit badly, especially for background reclaim where nr_to_reclaim equals to ULONG_MAX. Here we keep hitting cgroup A and potentially push it down to softlimit until the score drops to certain level. It is bad since it causes "hot" memory (under softlimit) of A being reclaimed while other cgroups has plenty of "cold" (above softlimit) to give out.
Look at the function reclaim_score(). Once a group drops below its soft limit, its score will be a factor 10000 smaller, making sure we hit the second exit condition. After that, we will pick another group.
In general, pick one cgroup to reclaim instead of round-robin is ok as long as we don't reclaim further down to the softlimit. The next question then is what's the next cgroup to reclaim if that doesn't give us enough.
Again, look at the function reclaim_score(). If there is a group above the softlimit, we pretty much guarantee we will reclaim from that group. If any reclaim will happen from another group, it will be absolutely minimal (taking recent_pressure from 0 to SWAP_CLUSTER_MAX, and then moving on to another group). -- All rights reversed -- 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>