On 05/13/2013 11:46 AM, Michal Hocko wrote: > Memcg soft reclaim has been traditionally triggered from the global > reclaim paths before calling shrink_zone. mem_cgroup_soft_limit_reclaim > then picked up a group which exceeds the soft limit the most and > reclaimed it with 0 priority to reclaim at least SWAP_CLUSTER_MAX pages. > > The infrastructure requires per-node-zone trees which hold over-limit > groups and keep them up-to-date (via memcg_check_events) which is not > cost free. Although this overhead hasn't turned out to be a bottle neck > the implementation is suboptimal because mem_cgroup_update_tree has no > idea which zones consumed memory over the limit so we could easily end > up having a group on a node-zone tree having only few pages from that > node-zone. > > This patch doesn't try to fix node-zone trees management because it > seems that integrating soft reclaim into zone shrinking sounds much > easier and more appropriate for several reasons. > First of all 0 priority reclaim was a crude hack which might lead to > big stalls if the group's LRUs are big and hard to reclaim (e.g. a lot > of dirty/writeback pages). > Soft reclaim should be applicable also to the targeted reclaim which is > awkward right now without additional hacks. > Last but not least the whole infrastructure eats quite some code. > > After this patch shrink_zone is done in 2 passes. First it tries to do the > soft reclaim if appropriate (only for global reclaim for now to keep > compatible with the original state) and fall back to ignoring soft limit > if no group is eligible to soft reclaim or nothing has been scanned > during the first pass. Only groups which are over their soft limit or > any of their parents up the hierarchy is over the limit are considered > eligible during the first pass. > > Soft limit tree which is not necessary anymore will be removed in the > follow up patch to make this patch smaller and easier to review. > > Changes since v1 > - __shrink_zone doesn't return the number of shrunk groups as nr_scanned > test covers both no groups scanned and no pages from the required zone > as pointed by Johannes > > Signed-off-by: Michal Hocko <mhocko@xxxxxxx> Patch looks fine to me Reviewed-by: Glauber Costa <glommer@xxxxxxxxxx> -- 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>