mm: make counting of list_lru_one::nr_items lockless
During the reclaiming slab of a memcg, shrink_slab iterates over all registered shrinkers in the system, and tries to count and consume objects related to the cgroup. In case of memory pressure, this behaves bad: I observe high system time and time spent in list_lru_count_one() for many processes on RHEL7 kernel. This patch makes list_lru_node::memcg_lrus rcu protected, that allows to skip taking spinlock in list_lru_count_one(). Shakeel Butt with the patch observes significant perf graph change. He says: ======================================================================== 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 ======================================================================== Thanks Shakeel for the testing. [ktkhai@virtuozzo.com: v2] Link: http://lkml.kernel.org/r/151203869520.3915.2587549826865799173.stgit@localhost.localdomain Link: http://lkml.kernel.org/r/150583358557.26700.8490036563698102569.stgit@localhost.localdomainSigned-off-by: NKirill Tkhai <ktkhai@virtuozzo.com> Tested-by: NShakeel Butt <shakeelb@google.com> Acked-by: NVladimir Davydov <vdavydov.dev@gmail.com> Cc: Andrey Ryabinin <aryabinin@virtuozzo.com> Cc: Michal Hocko <mhocko@kernel.org> Cc: Johannes Weiner <hannes@cmpxchg.org> Signed-off-by: NAndrew Morton <akpm@linux-foundation.org> Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
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