On Tue, Aug 22, 2017 at 03:29:35PM +0300, Kirill Tkhai 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
It would be nice to see how this is improved by this patch. Can you try to record the traces on the vanilla kernel with and without this patch? > > This patch aims to make super_cache_count() more effective. It > makes __list_lru_count_one() count nr_items lockless to minimize > overhead introducing by locking operation, and to make parallel > reclaims more scalable. > > The lock won't be taken on shrinker::count_objects(), > it would be taken only for the real shrink by the thread, > who realizes it. > > https://jira.sw.ru/browse/PSBM-69296 Not relevant.
