On Tue 12-02-19 14:45:42, Andrew Morton wrote: [...] > From: Chris Down <chris@xxxxxxxxxxxxxx> > Subject: mm, memcg: consider subtrees in memory.events > > memory.stat and other files already consider subtrees in their output, and > we should too in order to not present an inconsistent interface. > > The current situation is fairly confusing, because people interacting with > cgroups expect hierarchical behaviour in the vein of memory.stat, > cgroup.events, and other files. For example, this causes confusion when > debugging reclaim events under low, as currently these always read "0" at > non-leaf memcg nodes, which frequently causes people to misdiagnose breach > behaviour. The same confusion applies to other counters in this file when > debugging issues. > > Aggregation is done at write time instead of at read-time since these > counters aren't hot (unlike memory.stat which is per-page, so it does it > at read time), and it makes sense to bundle this with the file > notifications. > > After this patch, events are propagated up the hierarchy: > > [root@ktst ~]# cat /sys/fs/cgroup/system.slice/memory.events > low 0 > high 0 > max 0 > oom 0 > oom_kill 0 > [root@ktst ~]# systemd-run -p MemoryMax=1 true > Running as unit: run-r251162a189fb4562b9dabfdc9b0422f5.service > [root@ktst ~]# cat /sys/fs/cgroup/system.slice/memory.events > low 0 > high 0 > max 7 > oom 1 > oom_kill 1 > > As this is a change in behaviour, this can be reverted to the old > behaviour by mounting with the `memory_localevents' flag set. However, we > use the new behaviour by default as there's a lack of evidence that there > are any current users of memory.events that would find this change > undesirable. > > Link: http://lkml.kernel.org/r/20190208224419.GA24772@xxxxxxxxxxxxxx > Signed-off-by: Chris Down <chris@xxxxxxxxxxxxxx> > Acked-by: Johannes Weiner <hannes@xxxxxxxxxxx> > Cc: Michal Hocko <mhocko@xxxxxxxxxx> > Cc: Tejun Heo <tj@xxxxxxxxxx> > Cc: Roman Gushchin <guro@xxxxxx> > Cc: Dennis Zhou <dennis@xxxxxxxxxx> > Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> FTR: As I've already said here [1] I can live with this change as long as there is a larger consensus among cgroup v2 users. So let's give this some more time before merging to see whether there is such a consensus. [1] http://lkml.kernel.org/r/20190201102515.GK11599@xxxxxxxxxxxxxx > --- > > Documentation/admin-guide/cgroup-v2.rst | 9 +++++++++ > include/linux/cgroup-defs.h | 5 +++++ > include/linux/memcontrol.h | 10 ++++++++-- > kernel/cgroup/cgroup.c | 16 ++++++++++++++-- > 4 files changed, 36 insertions(+), 4 deletions(-) > > --- a/Documentation/admin-guide/cgroup-v2.rst~mm-consider-subtrees-in-memoryevents > +++ a/Documentation/admin-guide/cgroup-v2.rst > @@ -177,6 +177,15 @@ cgroup v2 currently supports the followi > ignored on non-init namespace mounts. Please refer to the > Delegation section for details. > > + memory_localevents > + > + Only populate memory.events with data for the current cgroup, > + and not any subtrees. This is legacy behaviour, the default > + behaviour without this option is to include subtree counts. > + This option is system wide and can only be set on mount or > + modified through remount from the init namespace. The mount > + option is ignored on non-init namespace mounts. > + > > Organizing Processes and Threads > -------------------------------- > --- a/include/linux/cgroup-defs.h~mm-consider-subtrees-in-memoryevents > +++ a/include/linux/cgroup-defs.h > @@ -83,6 +83,11 @@ enum { > * Enable cpuset controller in v1 cgroup to use v2 behavior. > */ > CGRP_ROOT_CPUSET_V2_MODE = (1 << 4), > + > + /* > + * Enable legacy local memory.events. > + */ > + CGRP_ROOT_MEMORY_LOCAL_EVENTS = (1 << 5), > }; > > /* cftype->flags */ > --- a/include/linux/memcontrol.h~mm-consider-subtrees-in-memoryevents > +++ a/include/linux/memcontrol.h > @@ -789,8 +789,14 @@ static inline void count_memcg_event_mm( > static inline void memcg_memory_event(struct mem_cgroup *memcg, > enum memcg_memory_event event) > { > - atomic_long_inc(&memcg->memory_events[event]); > - cgroup_file_notify(&memcg->events_file); > + do { > + atomic_long_inc(&memcg->memory_events[event]); > + cgroup_file_notify(&memcg->events_file); > + > + if (cgrp_dfl_root.flags & CGRP_ROOT_MEMORY_LOCAL_EVENTS) > + break; > + } while ((memcg = parent_mem_cgroup(memcg)) && > + !mem_cgroup_is_root(memcg)); > } > > static inline void memcg_memory_event_mm(struct mm_struct *mm, > --- a/kernel/cgroup/cgroup.c~mm-consider-subtrees-in-memoryevents > +++ a/kernel/cgroup/cgroup.c > @@ -1775,11 +1775,13 @@ int cgroup_show_path(struct seq_file *sf > > enum cgroup2_param { > Opt_nsdelegate, > + Opt_memory_localevents, > nr__cgroup2_params > }; > > static const struct fs_parameter_spec cgroup2_param_specs[] = { > - fsparam_flag ("nsdelegate", Opt_nsdelegate), > + fsparam_flag("nsdelegate", Opt_nsdelegate), > + fsparam_flag("memory_localevents", Opt_memory_localevents), > {} > }; > > @@ -1802,6 +1804,9 @@ static int cgroup2_parse_param(struct fs > case Opt_nsdelegate: > ctx->flags |= CGRP_ROOT_NS_DELEGATE; > return 0; > + case Opt_memory_localevents: > + ctx->flags |= CGRP_ROOT_MEMORY_LOCAL_EVENTS; > + return 0; > } > return -EINVAL; > } > @@ -1813,6 +1818,11 @@ static void apply_cgroup_root_flags(unsi > cgrp_dfl_root.flags |= CGRP_ROOT_NS_DELEGATE; > else > cgrp_dfl_root.flags &= ~CGRP_ROOT_NS_DELEGATE; > + > + if (root_flags & CGRP_ROOT_MEMORY_LOCAL_EVENTS) > + cgrp_dfl_root.flags |= CGRP_ROOT_MEMORY_LOCAL_EVENTS; > + else > + cgrp_dfl_root.flags &= ~CGRP_ROOT_MEMORY_LOCAL_EVENTS; > } > } > > @@ -1820,6 +1830,8 @@ static int cgroup_show_options(struct se > { > if (cgrp_dfl_root.flags & CGRP_ROOT_NS_DELEGATE) > seq_puts(seq, ",nsdelegate"); > + if (cgrp_dfl_root.flags & CGRP_ROOT_MEMORY_LOCAL_EVENTS) > + seq_puts(seq, ",memory_localevents"); > return 0; > } > > @@ -6207,7 +6219,7 @@ static struct kobj_attribute cgroup_dele > static ssize_t features_show(struct kobject *kobj, struct kobj_attribute *attr, > char *buf) > { > - return snprintf(buf, PAGE_SIZE, "nsdelegate\n"); > + return snprintf(buf, PAGE_SIZE, "nsdelegate\nmemory_localevents\n"); > } > static struct kobj_attribute cgroup_features_attr = __ATTR_RO(features); > > _ > > Patches currently in -mm which might be from chris@xxxxxxxxxxxxxx are > > mm-create-mem_cgroup_from_seq.patch > mm-extract-memcg-maxable-seq_file-logic-to-seq_show_memcg_tunable.patch > mm-proportional-memorylowmin-reclaim.patch > mm-proportional-memorylowmin-reclaim-fix.patch > mm-memcontrol-expose-thp-events-on-a-per-memcg-basis.patch > mm-memcontrol-expose-thp-events-on-a-per-memcg-basis-fix-2.patch > mm-make-memoryemin-the-baseline-for-utilisation-determination.patch > mm-rename-ambiguously-named-memorystat-counters-and-functions.patch > mm-consider-subtrees-in-memoryevents.patch -- Michal Hocko SUSE Labs
