On Tue, 19 Sep 2017 18:06:33 +0300 Kirill Tkhai <ktk...@virtuozzo.com> wrote:
> 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 (collected via $perf record --call-graph fp -j k -a): > > 0,50% nixstatsagent [kernel.vmlinux] [k] _raw_spin_lock [k] > _raw_spin_lock > 0,26% nixstatsagent [kernel.vmlinux] [k] shrink_slab [k] > shrink_slab > 0,23% nixstatsagent [kernel.vmlinux] [k] super_cache_count [k] > super_cache_count > 0,15% nixstatsagent [kernel.vmlinux] [k] __list_lru_count_one.isra.2 [k] > _raw_spin_lock > 0,15% nixstatsagent [kernel.vmlinux] [k] list_lru_count_one [k] > __list_lru_count_one.isra.2 > > 0,94% mysqld [kernel.vmlinux] [k] _raw_spin_lock [k] > _raw_spin_lock > 0,57% mysqld [kernel.vmlinux] [k] shrink_slab [k] > shrink_slab > 0,51% mysqld [kernel.vmlinux] [k] super_cache_count [k] > super_cache_count > 0,32% mysqld [kernel.vmlinux] [k] __list_lru_count_one.isra.2 [k] > _raw_spin_lock > 0,32% mysqld [kernel.vmlinux] [k] list_lru_count_one [k] > __list_lru_count_one.isra.2 > > 0,73% sshd [kernel.vmlinux] [k] _raw_spin_lock [k] > _raw_spin_lock > 0,35% sshd [kernel.vmlinux] [k] shrink_slab [k] > shrink_slab > 0,32% sshd [kernel.vmlinux] [k] super_cache_count [k] > super_cache_count > 0,21% sshd [kernel.vmlinux] [k] __list_lru_count_one.isra.2 [k] > _raw_spin_lock > 0,21% sshd [kernel.vmlinux] [k] list_lru_count_one [k] > __list_lru_count_one.isra.2 > > 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?
