On Fri, Sep 29, 2017 at 1:15 AM, Kirill Tkhai <ktkhai@xxxxxxxxxxxxx> wrote: > On 29.09.2017 00:02, Andrew Morton wrote: >> On Thu, 28 Sep 2017 10:48:55 +0300 Kirill Tkhai <ktkhai@xxxxxxxxxxxxx> wrote: >> >>>>> This patch aims to make super_cache_count() (and other functions, >>>>> which count LRU nr_items) more effective. >>>>> It allows list_lru_node::memcg_lrus to be RCU-accessed, and makes >>>>> __list_lru_count_one() count nr_items lockless to minimize >>>>> overhead introduced by locking operation, and to make parallel >>>>> reclaims more scalable. >>>> >>>> And... what were the effects of the patch? Did you not run the same >>>> performance tests after applying it? >>> >>> I've just detected the such high usage of shrink slab on production node. It's rather >>> difficult to make it use another kernel, than it uses, only kpatches are possible. >>> So, I haven't estimated how it acts on node's performance. >>> On test node I see, that the patch obviously removes raw_spin_lock from perf profile. >>> So, it's a little bit untested in this way. >> >> Well that's a problem. The patch increases list_lru.o text size by a >> lot (4800->5696) which will have a cost. And we don't have proof that >> any benefit is worth that cost. It shouldn't be too hard to cook up a >> synthetic test to trigger memcg slab reclaim and then run a >> before-n-after benchmark? > > Ok, then, please, ignore this for a while, I'll try to do it a little bit later. > I rebased this patch on linus tree (replacing kfree_rcu with call_rcu as there is no kvfree_rcu) and did some experiments. I think the patch is worth to be included. Setup: running a fork-bomb in a memcg of 200MiB on a 8GiB and 4 vcpu VM and recording the trace with 'perf record -g -a'. The trace without the patch: + 34.19% fb.sh [kernel.kallsyms] [k] queued_spin_lock_slowpath + 30.77% fb.sh [kernel.kallsyms] [k] _raw_spin_lock + 3.53% fb.sh [kernel.kallsyms] [k] list_lru_count_one + 2.26% fb.sh [kernel.kallsyms] [k] super_cache_count + 1.68% fb.sh [kernel.kallsyms] [k] shrink_slab + 0.59% fb.sh [kernel.kallsyms] [k] down_read_trylock + 0.48% fb.sh [kernel.kallsyms] [k] _raw_spin_unlock_irqrestore + 0.38% fb.sh [kernel.kallsyms] [k] shrink_node_memcg + 0.32% fb.sh [kernel.kallsyms] [k] queue_work_on + 0.26% fb.sh [kernel.kallsyms] [k] count_shadow_nodes With the patch: + 0.16% swapper [kernel.kallsyms] [k] default_idle + 0.13% oom_reaper [kernel.kallsyms] [k] mutex_spin_on_owner + 0.05% perf [kernel.kallsyms] [k] copy_user_generic_string + 0.05% init.real [kernel.kallsyms] [k] wait_consider_task + 0.05% kworker/0:0 [kernel.kallsyms] [k] finish_task_switch + 0.04% kworker/2:1 [kernel.kallsyms] [k] finish_task_switch + 0.04% kworker/3:1 [kernel.kallsyms] [k] finish_task_switch + 0.04% kworker/1:0 [kernel.kallsyms] [k] finish_task_switch + 0.03% binary [kernel.kallsyms] [k] copy_page Kirill, can you resend your patch with this info or do you want me send the rebased patch? -- 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>
