On Tue, 20 Mar 2018, Michal Hocko wrote: > > > > > Although SWAP_CLUSTER_MAX is used at the lower level, but the call > > > > > stack of try_to_free_mem_cgroup_pages is too long, increase the > > > > > nr_to_reclaim can reduce times of calling > > > > > function[do_try_to_free_pages, shrink_zones, hrink_node ] > > > > > > > > > > mem_cgroup_resize_limit > > > > > --->try_to_free_mem_cgroup_pages: .nr_to_reclaim = max(1024, > > > > > --->SWAP_CLUSTER_MAX), > > > > > ---> do_try_to_free_pages > > > > > ---> shrink_zones > > > > > --->shrink_node > > > > > ---> shrink_node_memcg > > > > > ---> shrink_list <-------loop will happen in this place > > > > [times=1024/32] > > > > > ---> shrink_page_list > > > > > > > > Can you actually measure this to be the culprit. Because we should rethink > > > > our call path if it is too complicated/deep to perform well. > > > > Adding arbitrary batch sizes doesn't sound like a good way to go to me. > > > > > > Ok, I will try > > > > > > > Looping in mem_cgroup_resize_limit(), which takes memcg_limit_mutex on > > every iteration which contends with lowering limits in other cgroups (on > > our systems, thousands), calling try_to_free_mem_cgroup_pages() with less > > than SWAP_CLUSTER_MAX is lame. > > Well, if the global lock is a bottleneck in your deployments then we > can come up with something more clever. E.g. per hierarchy locking > or even drop the lock for the reclaim altogether. If we reclaim in > SWAP_CLUSTER_MAX then the potential over-reclaim risk quite low when > multiple users are shrinking the same (sub)hierarchy. > I don't believe this to be a bottleneck if nr_pages is increased in mem_cgroup_resize_limit(). > > It would probably be best to limit the > > nr_pages to the amount that needs to be reclaimed, though, rather than > > over reclaiming. > > How do you achieve that? The charging path is not synchornized with the > shrinking one at all. > The point is to get a better guess at how many pages, up to SWAP_CLUSTER_MAX, that need to be reclaimed instead of 1. > > If you wanted to be invasive, you could change page_counter_limit() to > > return the count - limit, fix up the callers that look for -EBUSY, and > > then use max(val, SWAP_CLUSTER_MAX) as your nr_pages. > > I am not sure I understand > Have page_counter_limit() return the number of pages over limit, i.e. count - limit, since it compares the two anyway. Fix up existing callers and then clamp that value to SWAP_CLUSTER_MAX in mem_cgroup_resize_limit(). It's a more accurate guess than either 1 or 1024.
