On Mon, 19 Mar 2018, Li,Rongqing 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. It would probably be best to limit the nr_pages to the amount that needs to be reclaimed, though, rather than over reclaiming. 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.
