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mm/memcg: disable threshold event handlers on PREEMPT_RT

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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.

Link: https://lkml.kernel.org/r/20220226204144.1008339-3-bigeasy@linutronix.de
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>
Acked-by: Michal Hocko <mhocko@suse.com>
Cc: kernel test robot <oliver.sang@intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vladimir Davydov <vdavydov.dev@gmail.com>
Cc: Waiman Long <longman@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Sebastian Andrzej Siewior 2022-03-22 14:40:38 -07:00 committed by Linus Torvalds
parent fead2b8697
commit 2343e88d23
2 changed files with 14 additions and 2 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
Documentation/admin-guide/cgroup-v1/memory.rst
View File

@ -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

14
mm/memcontrol.c
View File

@ -858,6 +858,9 @@ 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);