On Wed, Jul 18, 2018 at 8:27 AM Bruce Merry <bmerry@xxxxxxxxx> wrote: > > On 18 July 2018 at 16:47, Michal Hocko <mhocko@xxxxxxxxxx> wrote: > >> Thanks for looking into this. I'm not familiar with ftrace. Can you > >> give me a specific command line to run? Based on "perf record cat > >> /sys/fs/cgroup/memory/memory.stat"/"perf report", I see the following: > >> > >> 42.09% cat [kernel.kallsyms] [k] memcg_stat_show > >> 29.19% cat [kernel.kallsyms] [k] memcg_sum_events.isra.22 > >> 12.41% cat [kernel.kallsyms] [k] mem_cgroup_iter > >> 5.42% cat [kernel.kallsyms] [k] _find_next_bit > >> 4.14% cat [kernel.kallsyms] [k] css_next_descendant_pre > >> 3.44% cat [kernel.kallsyms] [k] find_next_bit > >> 2.84% cat [kernel.kallsyms] [k] mem_cgroup_node_nr_lru_pages > > > > I would just use perf record as you did. How long did the call take? > > Also is the excessive time an outlier or a more consistent thing? If the > > former does perf record show any difference? > > I didn't note the exact time for that particular run, but it's pretty > consistently 372-377ms on the machine that has that perf report. The > times differ between machines showing the symptom (anywhere from > 200-500ms), but are consistent (within a few ms) in back-to-back runs > on each machine. > > >> Ubuntu 16.04 with kernel 4.13.0-41-generic (so presumably includes > >> some Ubuntu special sauce). > > > > Do you see the same whe running with the vanilla kernel? > > We don't currently have any boxes running vanilla kernels. While I > could install a test box with a vanilla kernel, I don't know how to > reproduce the problem, what piece of our production environment is > triggering it, or even why some machines are unaffected, so if the > problem didn't re-occur on the test box I wouldn't be able to conclude > anything useful. > > Do you have suggestions on things I could try that might trigger this? > e.g. are there cases where a cgroup no longer shows up in the > filesystem but is still lingering while waiting for its refcount to > hit zero? Does every child cgroup contribute to the stat_show cost of > its parent or does it have to have some non-trivial variation from its > parent? > The memcg tree does include all zombie memcgs and these zombies does contribute to the memcg_stat_show cost. Shakeel
