On Mon 19-03-18 10:00:41, Li,Rongqing wrote: > > > > -----邮件原件----- > > 发件人: Michal Hocko [mailto:mhocko@xxxxxxxxxx] > > 发送时间: 2018年3月19日 16:54 > > 收件人: Li,Rongqing <lirongqing@xxxxxxxxx> > > 抄送: linux-kernel@xxxxxxxxxxxxxxx; linux-mm@xxxxxxxxx; > > cgroups@xxxxxxxxxxxxxxx; hannes@xxxxxxxxxxx; Andrey Ryabinin > > <aryabinin@xxxxxxxxxxxxx> > > 主题: Re: [PATCH] mm/memcontrol.c: speed up to force empty a memory > > cgroup > > > > On Mon 19-03-18 16:29:30, Li RongQing wrote: > > > mem_cgroup_force_empty() tries to free only 32 (SWAP_CLUSTER_MAX) > > > pages on each iteration, if a memory cgroup has lots of page cache, it > > > will take many iterations to empty all page cache, so increase the > > > reclaimed number per iteration to speed it up. same as in > > > mem_cgroup_resize_limit() > > > > > > a simple test show: > > > > > > $dd if=aaa of=bbb bs=1k count=3886080 > > > $rm -f bbb > > > $time echo 100000000 >/cgroup/memory/test/memory.limit_in_bytes > > > > > > Before: 0m0.252s ===> after: 0m0.178s > > > > Andrey was proposing something similar [1]. My main objection was that his > > approach might lead to over-reclaim. Your approach is more conservative > > because it just increases the batch size. The size is still rather arbitrary. Same > > as SWAP_CLUSTER_MAX but that one is a commonly used unit of reclaim in > > the MM code. > > > > I would be really curious about more detailed explanation why having a > > larger batch yields to a better performance because we are doingg > > SWAP_CLUSTER_MAX batches at the lower reclaim level anyway. > > > > 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. -- Michal Hocko SUSE Labs
