On Wed, Aug 23, 2017 at 11:00:56AM +0300, Kirill Tkhai wrote: > On 22.08.2017 22:47, Vladimir Davydov wrote: > > 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? > > Sadly, the talk is about a production node, and it's impossible to use vanila > kernel there.
I see :-( Then maybe you could try to come up with a contrived test?
