diff mbox series

[v5,1/3] memcg: increase the valid index range for memcg stats

Message ID 20240724203322.2765486-2-pasha.tatashin@soleen.com (mailing list archive)
State New
Headers show
Series Kernel stack usage histogram | expand

Commit Message

Pasha Tatashin July 24, 2024, 8:33 p.m. UTC 
From: Shakeel Butt <shakeel.butt@linux.dev>

At the moment the valid index for the indirection tables for memcg stats
and events is < S8_MAX. These indirection tables are used in performance
critical codepaths. With the latest addition to the vm_events, the
NR_VM_EVENT_ITEMS has gone over S8_MAX. One way to resolve is to
increase the entry size of the indirection table from int8_t to int16_t
but this will increase the potential number of cachelines needed to
access the indirection table.

This patch took a different approach and make the valid index < U8_MAX.
In this way the size of the indirection tables will remain same and we
only need to invalid index check from less than 0 to equal to U8_MAX.
In this approach we have also removed a subtraction from the performance
critical codepaths.

Signed-off-by: Shakeel Butt <shakeel.butt@linux.dev>
Co-developed-by: Pasha Tatashin <pasha.tatashin@soleen.com>
Signed-off-by: Pasha Tatashin <pasha.tatashin@soleen.com>
---
 mm/memcontrol.c | 50 +++++++++++++++++++++++++++----------------------
 1 file changed, 28 insertions(+), 22 deletions(-)

Comments

Yosry Ahmed July 24, 2024, 11:17 p.m. UTC | #1 
On Wed, Jul 24, 2024 at 1:33 PM Pasha Tatashin
<pasha.tatashin@soleen.com> wrote:
>
> From: Shakeel Butt <shakeel.butt@linux.dev>
>
> At the moment the valid index for the indirection tables for memcg stats
> and events is < S8_MAX. These indirection tables are used in performance
> critical codepaths. With the latest addition to the vm_events, the
> NR_VM_EVENT_ITEMS has gone over S8_MAX. One way to resolve is to
> increase the entry size of the indirection table from int8_t to int16_t
> but this will increase the potential number of cachelines needed to
> access the indirection table.
>
> This patch took a different approach and make the valid index < U8_MAX.
> In this way the size of the indirection tables will remain same and we
> only need to invalid index check from less than 0 to equal to U8_MAX.
> In this approach we have also removed a subtraction from the performance
> critical codepaths.
>
> Signed-off-by: Shakeel Butt <shakeel.butt@linux.dev>
> Co-developed-by: Pasha Tatashin <pasha.tatashin@soleen.com>
> Signed-off-by: Pasha Tatashin <pasha.tatashin@soleen.com>
> ---
>  mm/memcontrol.c | 50 +++++++++++++++++++++++++++----------------------
>  1 file changed, 28 insertions(+), 22 deletions(-)
>
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index 960371788687..2fdeece7f1f8 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -320,24 +320,27 @@ static const unsigned int memcg_stat_items[] = {
>  #define NR_MEMCG_NODE_STAT_ITEMS ARRAY_SIZE(memcg_node_stat_items)
>  #define MEMCG_VMSTAT_SIZE (NR_MEMCG_NODE_STAT_ITEMS + \
>                            ARRAY_SIZE(memcg_stat_items))
> -static int8_t mem_cgroup_stats_index[MEMCG_NR_STAT] __read_mostly;
> +#define IS_INVALID(index) ((index) == U8_MAX)

The use of this macro extends well into this file, should we use a
more specific name (e.g. IS_VALID_STATS_IDX())?
Pasha Tatashin July 25, 2024, 2:25 p.m. UTC | #2 
> >  #define NR_MEMCG_NODE_STAT_ITEMS ARRAY_SIZE(memcg_node_stat_items)
> >  #define MEMCG_VMSTAT_SIZE (NR_MEMCG_NODE_STAT_ITEMS + \
> >                            ARRAY_SIZE(memcg_stat_items))
> > -static int8_t mem_cgroup_stats_index[MEMCG_NR_STAT] __read_mostly;
> > +#define IS_INVALID(index) ((index) == U8_MAX)
>
> The use of this macro extends well into this file, should we use a
> more specific name (e.g. IS_VALID_STATS_IDX())?

I will redefine it like this:
#define BAD_STAT_IDX(index) ((u32)(index) >= U8_MAX)

1. A descriptive yet short name.
2. Check if the index is equal or larger than U8_MAX, which feels safer.

Pasha
diff mbox series

Patch

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 960371788687..2fdeece7f1f8 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -320,24 +320,27 @@  static const unsigned int memcg_stat_items[] = {
 #define NR_MEMCG_NODE_STAT_ITEMS ARRAY_SIZE(memcg_node_stat_items)
 #define MEMCG_VMSTAT_SIZE (NR_MEMCG_NODE_STAT_ITEMS + \
 			   ARRAY_SIZE(memcg_stat_items))
-static int8_t mem_cgroup_stats_index[MEMCG_NR_STAT] __read_mostly;
+#define IS_INVALID(index) ((index) == U8_MAX)
+static u8 mem_cgroup_stats_index[MEMCG_NR_STAT] __read_mostly;
 
 static void init_memcg_stats(void)
 {
-	int8_t i, j = 0;
+	u8 i, j = 0;
 
-	BUILD_BUG_ON(MEMCG_NR_STAT >= S8_MAX);
+	BUILD_BUG_ON(MEMCG_NR_STAT >= U8_MAX);
 
-	for (i = 0; i < NR_MEMCG_NODE_STAT_ITEMS; ++i)
-		mem_cgroup_stats_index[memcg_node_stat_items[i]] = ++j;
+	memset(mem_cgroup_stats_index, U8_MAX, sizeof(mem_cgroup_stats_index));
 
-	for (i = 0; i < ARRAY_SIZE(memcg_stat_items); ++i)
-		mem_cgroup_stats_index[memcg_stat_items[i]] = ++j;
+	for (i = 0; i < NR_MEMCG_NODE_STAT_ITEMS; ++i, ++j)
+		mem_cgroup_stats_index[memcg_node_stat_items[i]] = j;
+
+	for (i = 0; i < ARRAY_SIZE(memcg_stat_items); ++i, ++j)
+		mem_cgroup_stats_index[memcg_stat_items[i]] = j;
 }
 
 static inline int memcg_stats_index(int idx)
 {
-	return mem_cgroup_stats_index[idx] - 1;
+	return mem_cgroup_stats_index[idx];
 }
 
 struct lruvec_stats_percpu {
@@ -369,7 +372,7 @@  unsigned long lruvec_page_state(struct lruvec *lruvec, enum node_stat_item idx)
 		return node_page_state(lruvec_pgdat(lruvec), idx);
 
 	i = memcg_stats_index(idx);
-	if (WARN_ONCE(i < 0, "%s: missing stat item %d\n", __func__, idx))
+	if (WARN_ONCE(IS_INVALID(i), "%s: missing stat item %d\n", __func__, idx))
 		return 0;
 
 	pn = container_of(lruvec, struct mem_cgroup_per_node, lruvec);
@@ -392,7 +395,7 @@  unsigned long lruvec_page_state_local(struct lruvec *lruvec,
 		return node_page_state(lruvec_pgdat(lruvec), idx);
 
 	i = memcg_stats_index(idx);
-	if (WARN_ONCE(i < 0, "%s: missing stat item %d\n", __func__, idx))
+	if (WARN_ONCE(IS_INVALID(i), "%s: missing stat item %d\n", __func__, idx))
 		return 0;
 
 	pn = container_of(lruvec, struct mem_cgroup_per_node, lruvec);
@@ -435,21 +438,24 @@  static const unsigned int memcg_vm_event_stat[] = {
 };
 
 #define NR_MEMCG_EVENTS ARRAY_SIZE(memcg_vm_event_stat)
-static int8_t mem_cgroup_events_index[NR_VM_EVENT_ITEMS] __read_mostly;
+static u8 mem_cgroup_events_index[NR_VM_EVENT_ITEMS] __read_mostly;
 
 static void init_memcg_events(void)
 {
-	int8_t i;
+	u8 i;
+
+	BUILD_BUG_ON(NR_VM_EVENT_ITEMS >= U8_MAX);
 
-	BUILD_BUG_ON(NR_VM_EVENT_ITEMS >= S8_MAX);
+	memset(mem_cgroup_events_index, U8_MAX,
+	       sizeof(mem_cgroup_events_index));
 
 	for (i = 0; i < NR_MEMCG_EVENTS; ++i)
-		mem_cgroup_events_index[memcg_vm_event_stat[i]] = i + 1;
+		mem_cgroup_events_index[memcg_vm_event_stat[i]] = i;
 }
 
 static inline int memcg_events_index(enum vm_event_item idx)
 {
-	return mem_cgroup_events_index[idx] - 1;
+	return mem_cgroup_events_index[idx];
 }
 
 struct memcg_vmstats_percpu {
@@ -621,7 +627,7 @@  unsigned long memcg_page_state(struct mem_cgroup *memcg, int idx)
 	long x;
 	int i = memcg_stats_index(idx);
 
-	if (WARN_ONCE(i < 0, "%s: missing stat item %d\n", __func__, idx))
+	if (WARN_ONCE(IS_INVALID(i), "%s: missing stat item %d\n", __func__, idx))
 		return 0;
 
 	x = READ_ONCE(memcg->vmstats->state[i]);
@@ -662,7 +668,7 @@  void __mod_memcg_state(struct mem_cgroup *memcg, enum memcg_stat_item idx,
 	if (mem_cgroup_disabled())
 		return;
 
-	if (WARN_ONCE(i < 0, "%s: missing stat item %d\n", __func__, idx))
+	if (WARN_ONCE(IS_INVALID(i), "%s: missing stat item %d\n", __func__, idx))
 		return;
 
 	__this_cpu_add(memcg->vmstats_percpu->state[i], val);
@@ -675,7 +681,7 @@  unsigned long memcg_page_state_local(struct mem_cgroup *memcg, int idx)
 	long x;
 	int i = memcg_stats_index(idx);
 
-	if (WARN_ONCE(i < 0, "%s: missing stat item %d\n", __func__, idx))
+	if (WARN_ONCE(IS_INVALID(i), "%s: missing stat item %d\n", __func__, idx))
 		return 0;
 
 	x = READ_ONCE(memcg->vmstats->state_local[i]);
@@ -694,7 +700,7 @@  static void __mod_memcg_lruvec_state(struct lruvec *lruvec,
 	struct mem_cgroup *memcg;
 	int i = memcg_stats_index(idx);
 
-	if (WARN_ONCE(i < 0, "%s: missing stat item %d\n", __func__, idx))
+	if (WARN_ONCE(IS_INVALID(i), "%s: missing stat item %d\n", __func__, idx))
 		return;
 
 	pn = container_of(lruvec, struct mem_cgroup_per_node, lruvec);
@@ -810,7 +816,7 @@  void __count_memcg_events(struct mem_cgroup *memcg, enum vm_event_item idx,
 	if (mem_cgroup_disabled())
 		return;
 
-	if (WARN_ONCE(i < 0, "%s: missing stat item %d\n", __func__, idx))
+	if (WARN_ONCE(IS_INVALID(i), "%s: missing stat item %d\n", __func__, idx))
 		return;
 
 	memcg_stats_lock();
@@ -823,7 +829,7 @@  unsigned long memcg_events(struct mem_cgroup *memcg, int event)
 {
 	int i = memcg_events_index(event);
 
-	if (WARN_ONCE(i < 0, "%s: missing stat item %d\n", __func__, event))
+	if (WARN_ONCE(IS_INVALID(i), "%s: missing stat item %d\n", __func__, event))
 		return 0;
 
 	return READ_ONCE(memcg->vmstats->events[i]);
@@ -833,7 +839,7 @@  unsigned long memcg_events_local(struct mem_cgroup *memcg, int event)
 {
 	int i = memcg_events_index(event);
 
-	if (WARN_ONCE(i < 0, "%s: missing stat item %d\n", __func__, event))
+	if (WARN_ONCE(IS_INVALID(i), "%s: missing stat item %d\n", __func__, event))
 		return 0;
 
 	return READ_ONCE(memcg->vmstats->events_local[i]);