On Fri 23-03-18 02:58:36, Li,Rongqing wrote: > > > > -----邮件原件----- > > 发件人: linux-kernel-owner@xxxxxxxxxxxxxxx > > [mailto:linux-kernel-owner@xxxxxxxxxxxxxxx] 代表 Li,Rongqing > > 发送时间: 2018年3月19日 18:52 > > 收件人: Michal Hocko <mhocko@xxxxxxxxxx> > > 抄送: linux-kernel@xxxxxxxxxxxxxxx; linux-mm@xxxxxxxxx; > > cgroups@xxxxxxxxxxxxxxx; hannes@xxxxxxxxxxx; Andrey Ryabinin > > <aryabinin@xxxxxxxxxxxxx> > > 主题: 答复: 答复: [PATCH] mm/memcontrol.c: speed up to force empty a > > memory cgroup > > > > > > > > > -----邮件原件----- > > > 发件人: Michal Hocko [mailto:mhocko@xxxxxxxxxx] > > > 发送时间: 2018年3月19日 18:38 > > > 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: 答复: [PATCH] mm/memcontrol.c: speed up to force empty a > > memory > > > cgroup > > > > > > 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. > > > > Ok, I will try > > > http://pasted.co/4edbcfff > > This is result from ftrace graph, it maybe prove that the deep call > path leads to low performance. Does it? Let's have a look at the condensed output: 6) | try_to_free_mem_cgroup_pages() { 6) | mem_cgroup_select_victim_node() { 6) 0.320 us | mem_cgroup_node_nr_lru_pages(); 6) 0.151 us | mem_cgroup_node_nr_lru_pages(); 6) 2.190 us | } 6) | do_try_to_free_pages() { 6) | shrink_node() { 6) | shrink_node_memcg() { 6) | shrink_inactive_list() { 6) + 23.131 us | shrink_page_list(); 6) + 33.960 us | } 6) + 39.203 us | } 6) | shrink_slab() { 6) + 72.955 us | } 6) ! 116.529 us | } 6) | shrink_node() { 6) 0.050 us | mem_cgroup_iter(); 6) 0.035 us | mem_cgroup_low(); 6) | shrink_node_memcg() { 6) 3.955 us | } 6) | shrink_slab() { 6) + 54.296 us | } 6) + 61.502 us | } 6) ! 185.020 us | } 6) ! 188.165 us | } try_to_free_mem_cgroup_pages is the full memcg reclaim path taking 188,165 us. The pure reclaim path is shrink_node and that took 116+61 = 177 us. So we have 11us spent on the way. Is this really making such a difference? How does the profile look when we do larger batches? > And when increase reclaiming page in try_to_free_mem_cgroup_pages, it > can reduce calling of shrink_slab, which save times, in my cases, page > caches occupy most memory, slab is little, but shrink_slab will be > called everytime OK, that makes more sense! shrink_slab is clearly visible here. It is more expensive than the page reclaim. This is something to look into. Thanks! -- Michal Hocko SUSE Labs
