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memcg: add tracing for memcg stat updates

PATCH Applied Shakeel Butt 3 participants 3 messages Oct 15, 2024 – Oct 16, 2024

Subsystems (4)
Memory management Tracing cgroup memcg
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Shakeel Butt

author maintainer
#0 lore raw

PATCH v2 1/1 memcg: add tracing for memcg stat updates

The memcg stats are maintained in rstat infrastructure which provides very fast updates side and reasonable read side. However memcg added plethora of stats and made the read side, which is cgroup rstat flush, very slow. To solve that, threshold was added in the memcg stats read side i.e. no need to flush the stats if updates are within the threshold.

This threshold based improvement worked for sometime but more stats were added to memcg and also the read codepath was getting triggered in the performance sensitive paths which made threshold based ratelimiting ineffective. We need more visibility into the hot and cold stats i.e. stats with a lot of updates. Let's add trace to get that visibility.

Signed-off-by Shakeel Butt <[email protected]>
Acked-by Roman Gushchin <[email protected]>
Reviewed-by Yosry Ahmed <[email protected]>
Cc Michal Hocko <[email protected]>
Cc Johannes Weiner <[email protected]>
Cc Muchun Song <[email protected]>
Cc JP Kobryn <[email protected]>
Cc Steven Rostedt (Google) <[email protected]>
Cc Andrew Morton <[email protected]>

---
Changes since v1:
- Used unsigned long type for memcg_rstat_events (Yosry)
- Kept the Acks and Reviews tag

 include/trace/events/memcg.h | 81 ++++++++++++++++++++++++++++++++++++
 mm/memcontrol.c              | 13 +++++-
 2 files changed, 92 insertions(+), 2 deletions(-)
 create mode 100644 include/trace/events/memcg.h
include/trace/events/memcg.h new file +81 -0
new file mode 100644
index 000000000000..8667e57816d2
@@ -0,0 +1,81 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#undef TRACE_SYSTEM
+#define TRACE_SYSTEM memcg
+
+#if !defined(_TRACE_MEMCG_H) || defined(TRACE_HEADER_MULTI_READ)
+#define _TRACE_MEMCG_H
+
+#include <linux/memcontrol.h>
+#include <linux/tracepoint.h>
+
+
+DECLARE_EVENT_CLASS(memcg_rstat_stats,
+
+	TP_PROTO(struct mem_cgroup *memcg, int item, int val),
+
+	TP_ARGS(memcg, item, val),
+
+	TP_STRUCT__entry(
+		__field(u64, id)
+		__field(int, item)
+		__field(int, val)
+	),
+
+	TP_fast_assign(
+		__entry->id = cgroup_id(memcg->css.cgroup);
+		__entry->item = item;
+		__entry->val = val;
+	),
+
+	TP_printk("memcg_id=%llu item=%d val=%d",
+		  __entry->id, __entry->item, __entry->val)
+);
+
+DEFINE_EVENT(memcg_rstat_stats, mod_memcg_state,
+
+	TP_PROTO(struct mem_cgroup *memcg, int item, int val),
+
+	TP_ARGS(memcg, item, val)
+);
+
+DEFINE_EVENT(memcg_rstat_stats, mod_memcg_lruvec_state,
+
+	TP_PROTO(struct mem_cgroup *memcg, int item, int val),
+
+	TP_ARGS(memcg, item, val)
+);
+
+DECLARE_EVENT_CLASS(memcg_rstat_events,
+
+	TP_PROTO(struct mem_cgroup *memcg, int item, unsigned long val),
+
+	TP_ARGS(memcg, item, val),
+
+	TP_STRUCT__entry(
+		__field(u64, id)
+		__field(int, item)
+		__field(unsigned long, val)
+	),
+
+	TP_fast_assign(
+		__entry->id = cgroup_id(memcg->css.cgroup);
+		__entry->item = item;
+		__entry->val = val;
+	),
+
+	TP_printk("memcg_id=%llu item=%d val=%lu",
+		  __entry->id, __entry->item, __entry->val)
+);
+
+DEFINE_EVENT(memcg_rstat_events, count_memcg_events,
+
+	TP_PROTO(struct mem_cgroup *memcg, int item, unsigned long val),
+
+	TP_ARGS(memcg, item, val)
+);
+
+
+#endif /* _TRACE_MEMCG_H */
+
+/* This part must be outside protection */
+#include <trace/define_trace.h>
mm/memcontrol.c +11 -2
index c098fd7f5c5e..17af08367c68 100644
@@ -71,6 +71,10 @@
 
 #include <linux/uaccess.h>
 
+#define CREATE_TRACE_POINTS
+#include <trace/events/memcg.h>
+#undef CREATE_TRACE_POINTS
+
 #include <trace/events/vmscan.h>
 
 struct cgroup_subsys memory_cgrp_subsys __read_mostly;

@@ -682,7 +686,9 @@ void __mod_memcg_state(struct mem_cgroup *memcg, enum memcg_stat_item idx,
 		return;
 
 	__this_cpu_add(memcg->vmstats_percpu->state[i], val);
-	memcg_rstat_updated(memcg, memcg_state_val_in_pages(idx, val));
+	val = memcg_state_val_in_pages(idx, val);
+	memcg_rstat_updated(memcg, val);
+	trace_mod_memcg_state(memcg, idx, val);
 }
 
 /* idx can be of type enum memcg_stat_item or node_stat_item. */

@@ -741,7 +747,9 @@ static void __mod_memcg_lruvec_state(struct lruvec *lruvec,
 	/* Update lruvec */
 	__this_cpu_add(pn->lruvec_stats_percpu->state[i], val);
 
-	memcg_rstat_updated(memcg, memcg_state_val_in_pages(idx, val));
+	val = memcg_state_val_in_pages(idx, val);
+	memcg_rstat_updated(memcg, val);
+	trace_mod_memcg_lruvec_state(memcg, idx, val);
 	memcg_stats_unlock();
 }
 

@@ -832,6 +840,7 @@ void __count_memcg_events(struct mem_cgroup *memcg, enum vm_event_item idx,
 	memcg_stats_lock();
 	__this_cpu_add(memcg->vmstats_percpu->events[i], count);
 	memcg_rstat_updated(memcg, count);
+	trace_count_memcg_events(memcg, idx, count);
 	memcg_stats_unlock();
 }
Signature · 1 line
2.43.5
maintainer Acked-by on v2 1/1
#1 lore raw
Quoted 12 lines · Shakeel Butt

The memcg stats are maintained in rstat infrastructure which provides very fast updates side and reasonable read side. However memcg added plethora of stats and made the read side, which is cgroup rstat flush, very slow. To solve that, threshold was added in the memcg stats read side i.e. no need to flush the stats if updates are within the threshold.

This threshold based improvement worked for sometime but more stats were added to memcg and also the read codepath was getting triggered in the performance sensitive paths which made threshold based ratelimiting ineffective. We need more visibility into the hot and cold stats i.e. stats with a lot of updates. Let's add trace to get that visibility.

Quoted 9 lines
Signed-off-by Shakeel Butt <[email protected]>
Acked-by Roman Gushchin <[email protected]>
Reviewed-by Yosry Ahmed <[email protected]>
Cc Michal Hocko <[email protected]>
Cc Johannes Weiner <[email protected]>
Cc Muchun Song <[email protected]>
Cc JP Kobryn <[email protected]>
Cc Steven Rostedt (Google) <[email protected]>
Cc Andrew Morton <[email protected]>
Acked-by Johannes Weiner <[email protected]>
Reviewed-by on v2 1/1
#2 lore raw
In reply to Shakeel Butt
Quoted 13 lines · Shakeel Butt

The memcg stats are maintained in rstat infrastructure which provides very fast updates side and reasonable read side. However memcg added plethora of stats and made the read side, which is cgroup rstat flush, very slow. To solve that, threshold was added in the memcg stats read side i.e. no need to flush the stats if updates are within the threshold.

This threshold based improvement worked for sometime but more stats were added to memcg and also the read codepath was getting triggered in the performance sensitive paths which made threshold based ratelimiting ineffective. We need more visibility into the hot and cold stats i.e. stats with a lot of updates. Let's add trace to get that visibility.

Quoted 9 lines
Signed-off-by Shakeel Butt <[email protected]>
Acked-by Roman Gushchin <[email protected]>
Reviewed-by Yosry Ahmed <[email protected]>
Cc Michal Hocko <[email protected]>
Cc Johannes Weiner <[email protected]>
Cc Muchun Song <[email protected]>
Cc JP Kobryn <[email protected]>
Cc Steven Rostedt (Google) <[email protected]>
Cc Andrew Morton <[email protected]>
Reviewed-by T.J. Mercier <[email protected]>