| Message ID | 20220217094802.3644569-3-bigeasy@linutronix.de (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | mm/memcg: Address PREEMPT_RT problems instead of disabling it. | expand |
On Thu, Feb 17, 2022 at 1:48 AM Sebastian Andrzej Siewior <bigeasy@linutronix.de> wrote: > > During the integration of PREEMPT_RT support, the code flow around > memcg_check_events() resulted in `twisted code'. Moving the code around > and avoiding then would then lead to an additional local-irq-save > section within memcg_check_events(). While looking better, it adds a > local-irq-save section to code flow which is usually within an > local-irq-off block on non-PREEMPT_RT configurations. > > The threshold event handler is a deprecated memcg v1 feature. Instead of > trying to get it to work under PREEMPT_RT just disable it. There should > be no users on PREEMPT_RT. From that perspective it makes even less > sense to get it to work under PREEMPT_RT while having zero users. > > Make memory.soft_limit_in_bytes and cgroup.event_control return > -EOPNOTSUPP on PREEMPT_RT. Make an empty memcg_check_events() and > memcg_write_event_control() which return only -EOPNOTSUPP on PREEMPT_RT. > Document that the two knobs are disabled on PREEMPT_RT. > > Suggested-by: Michal Hocko <mhocko@kernel.org> > Suggested-by: Michal Koutný <mkoutny@suse.com> > Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de> > Acked-by: Roman Gushchin <guro@fb.com> > Acked-by: Johannes Weiner <hannes@cmpxchg.org> Reviewed-by: Shakeel Butt <shakeelb@google.com>
On Thu 17-02-22 10:47:59, Sebastian Andrzej Siewior wrote: > During the integration of PREEMPT_RT support, the code flow around > memcg_check_events() resulted in `twisted code'. Moving the code around > and avoiding then would then lead to an additional local-irq-save > section within memcg_check_events(). While looking better, it adds a > local-irq-save section to code flow which is usually within an > local-irq-off block on non-PREEMPT_RT configurations. > > The threshold event handler is a deprecated memcg v1 feature. Instead of > trying to get it to work under PREEMPT_RT just disable it. There should > be no users on PREEMPT_RT. From that perspective it makes even less > sense to get it to work under PREEMPT_RT while having zero users. > > Make memory.soft_limit_in_bytes and cgroup.event_control return > -EOPNOTSUPP on PREEMPT_RT. Make an empty memcg_check_events() and > memcg_write_event_control() which return only -EOPNOTSUPP on PREEMPT_RT. > Document that the two knobs are disabled on PREEMPT_RT. > > Suggested-by: Michal Hocko <mhocko@kernel.org> > Suggested-by: Michal Koutný <mkoutny@suse.com> > Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de> > Acked-by: Roman Gushchin <guro@fb.com> > Acked-by: Johannes Weiner <hannes@cmpxchg.org> Acked-by: Michal Hocko <mhocko@suse.com> Thanks! > --- > Documentation/admin-guide/cgroup-v1/memory.rst | 2 ++ > mm/memcontrol.c | 14 ++++++++++++-- > 2 files changed, 14 insertions(+), 2 deletions(-) > > diff --git a/Documentation/admin-guide/cgroup-v1/memory.rst b/Documentation/admin-guide/cgroup-v1/memory.rst > index faac50149a222..2cc502a75ef64 100644 > --- a/Documentation/admin-guide/cgroup-v1/memory.rst > +++ b/Documentation/admin-guide/cgroup-v1/memory.rst > @@ -64,6 +64,7 @@ Brief summary of control files. > threads > cgroup.procs show list of processes > cgroup.event_control an interface for event_fd() > + This knob is not available on CONFIG_PREEMPT_RT systems. > memory.usage_in_bytes show current usage for memory > (See 5.5 for details) > memory.memsw.usage_in_bytes show current usage for memory+Swap > @@ -75,6 +76,7 @@ Brief summary of control files. > memory.max_usage_in_bytes show max memory usage recorded > memory.memsw.max_usage_in_bytes show max memory+Swap usage recorded > memory.soft_limit_in_bytes set/show soft limit of memory usage > + This knob is not available on CONFIG_PREEMPT_RT systems. > memory.stat show various statistics > memory.use_hierarchy set/show hierarchical account enabled > This knob is deprecated and shouldn't be > diff --git a/mm/memcontrol.c b/mm/memcontrol.c > index 8ab2dc75e70ec..0b5117ed2ae08 100644 > --- a/mm/memcontrol.c > +++ b/mm/memcontrol.c > @@ -859,6 +859,9 @@ static bool mem_cgroup_event_ratelimit(struct mem_cgroup *memcg, > */ > static void memcg_check_events(struct mem_cgroup *memcg, int nid) > { > + if (IS_ENABLED(CONFIG_PREEMPT_RT)) > + return; > + > /* threshold event is triggered in finer grain than soft limit */ > if (unlikely(mem_cgroup_event_ratelimit(memcg, > MEM_CGROUP_TARGET_THRESH))) { > @@ -3731,8 +3734,12 @@ static ssize_t mem_cgroup_write(struct kernfs_open_file *of, > } > break; > case RES_SOFT_LIMIT: > - memcg->soft_limit = nr_pages; > - ret = 0; > + if (IS_ENABLED(CONFIG_PREEMPT_RT)) { > + ret = -EOPNOTSUPP; > + } else { > + memcg->soft_limit = nr_pages; > + ret = 0; > + } > break; > } > return ret ?: nbytes; > @@ -4708,6 +4715,9 @@ static ssize_t memcg_write_event_control(struct kernfs_open_file *of, > char *endp; > int ret; > > + if (IS_ENABLED(CONFIG_PREEMPT_RT)) > + return -EOPNOTSUPP; > + > buf = strstrip(buf); > > efd = simple_strtoul(buf, &endp, 10); > -- > 2.34.1
diff --git a/Documentation/admin-guide/cgroup-v1/memory.rst b/Documentation/admin-guide/cgroup-v1/memory.rst index faac50149a222..2cc502a75ef64 100644 --- a/Documentation/admin-guide/cgroup-v1/memory.rst +++ b/Documentation/admin-guide/cgroup-v1/memory.rst @@ -64,6 +64,7 @@ Brief summary of control files. threads cgroup.procs show list of processes cgroup.event_control an interface for event_fd() + This knob is not available on CONFIG_PREEMPT_RT systems. memory.usage_in_bytes show current usage for memory (See 5.5 for details) memory.memsw.usage_in_bytes show current usage for memory+Swap @@ -75,6 +76,7 @@ Brief summary of control files. memory.max_usage_in_bytes show max memory usage recorded memory.memsw.max_usage_in_bytes show max memory+Swap usage recorded memory.soft_limit_in_bytes set/show soft limit of memory usage + This knob is not available on CONFIG_PREEMPT_RT systems. memory.stat show various statistics memory.use_hierarchy set/show hierarchical account enabled This knob is deprecated and shouldn't be diff --git a/mm/memcontrol.c b/mm/memcontrol.c index 8ab2dc75e70ec..0b5117ed2ae08 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -859,6 +859,9 @@ static bool mem_cgroup_event_ratelimit(struct mem_cgroup *memcg, */ static void memcg_check_events(struct mem_cgroup *memcg, int nid) { + if (IS_ENABLED(CONFIG_PREEMPT_RT)) + return; + /* threshold event is triggered in finer grain than soft limit */ if (unlikely(mem_cgroup_event_ratelimit(memcg, MEM_CGROUP_TARGET_THRESH))) { @@ -3731,8 +3734,12 @@ static ssize_t mem_cgroup_write(struct kernfs_open_file *of, } break; case RES_SOFT_LIMIT: - memcg->soft_limit = nr_pages; - ret = 0; + if (IS_ENABLED(CONFIG_PREEMPT_RT)) { + ret = -EOPNOTSUPP; + } else { + memcg->soft_limit = nr_pages; + ret = 0; + } break; } return ret ?: nbytes; @@ -4708,6 +4715,9 @@ static ssize_t memcg_write_event_control(struct kernfs_open_file *of, char *endp; int ret; + if (IS_ENABLED(CONFIG_PREEMPT_RT)) + return -EOPNOTSUPP; + buf = strstrip(buf); efd = simple_strtoul(buf, &endp, 10);