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Subject[PATCH v3 1/2] pcpcntr: add group allocation/free
Date
Allocations and frees are globally serialized on the pcpu lock (and the
CPU hotplug lock if enabled, which is the case on Debian).

At least one frequent consumer allocates 4 back-to-back counters (and
frees them in the same manner), exacerbating the problem.

While this does not fully remedy scalability issues, it is a step
towards that goal and provides immediate relief.

Signed-off-by: Mateusz Guzik <mjguzik@gmail.com>
---
include/linux/percpu_counter.h | 39 ++++++++++++++++++----
lib/percpu_counter.c | 61 +++++++++++++++++++++++-----------
2 files changed, 74 insertions(+), 26 deletions(-)

diff --git a/include/linux/percpu_counter.h b/include/linux/percpu_counter.h
index 75b73c83bc9d..f1e7c987e3d3 100644
--- a/include/linux/percpu_counter.h
+++ b/include/linux/percpu_counter.h
@@ -30,17 +30,27 @@ struct percpu_counter {

extern int percpu_counter_batch;

-int __percpu_counter_init(struct percpu_counter *fbc, s64 amount, gfp_t gfp,
- struct lock_class_key *key);
+int __percpu_counter_init_many(struct percpu_counter *fbc, s64 amount, gfp_t gfp,
+ u32 nr_counters, struct lock_class_key *key);

-#define percpu_counter_init(fbc, value, gfp) \
+#define percpu_counter_init_many(fbc, value, gfp, nr_counters) \
({ \
static struct lock_class_key __key; \
\
- __percpu_counter_init(fbc, value, gfp, &__key); \
+ __percpu_counter_init_many(fbc, value, gfp, nr_counters,\
+ &__key); \
})

-void percpu_counter_destroy(struct percpu_counter *fbc);
+
+#define percpu_counter_init(fbc, value, gfp) \
+ percpu_counter_init_many(fbc, value, gfp, 1)
+
+void percpu_counter_destroy_many(struct percpu_counter *fbc, u32 nr_counters);
+static inline void percpu_counter_destroy(struct percpu_counter *fbc)
+{
+ percpu_counter_destroy_many(fbc, 1);
+}
+
void percpu_counter_set(struct percpu_counter *fbc, s64 amount);
void percpu_counter_add_batch(struct percpu_counter *fbc, s64 amount,
s32 batch);
@@ -116,11 +126,26 @@ struct percpu_counter {
s64 count;
};

+static inline int percpu_counter_init_many(struct percpu_counter *fbc, s64 amount,
+ gfp_t gfp, u32 nr_counters)
+{
+ u32 i;
+
+ for (i = 0; i < nr_counters; i++)
+ fbc[i].count = amount;
+
+ return 0;
+}
+
static inline int percpu_counter_init(struct percpu_counter *fbc, s64 amount,
gfp_t gfp)
{
- fbc->count = amount;
- return 0;
+ return percpu_counter_init_many(fbc, amount, gfp, 1);
+}
+
+static inline void percpu_counter_destroy_many(struct percpu_counter *fbc,
+ u32 nr_counters)
+{
}

static inline void percpu_counter_destroy(struct percpu_counter *fbc)
diff --git a/lib/percpu_counter.c b/lib/percpu_counter.c
index 5004463c4f9f..9338b27f1cdd 100644
--- a/lib/percpu_counter.c
+++ b/lib/percpu_counter.c
@@ -151,48 +151,71 @@ s64 __percpu_counter_sum(struct percpu_counter *fbc)
}
EXPORT_SYMBOL(__percpu_counter_sum);

-int __percpu_counter_init(struct percpu_counter *fbc, s64 amount, gfp_t gfp,
- struct lock_class_key *key)
+int __percpu_counter_init_many(struct percpu_counter *fbc, s64 amount, gfp_t gfp,
+ u32 nr_counters, struct lock_class_key *key)
{
unsigned long flags __maybe_unused;
-
- raw_spin_lock_init(&fbc->lock);
- lockdep_set_class(&fbc->lock, key);
- fbc->count = amount;
- fbc->counters = alloc_percpu_gfp(s32, gfp);
- if (!fbc->counters)
+ size_t counter_size;
+ s32 __percpu *counters;
+ u32 i;
+
+ counter_size = ALIGN(sizeof(*counters), __alignof__(*counters));
+ counters = __alloc_percpu_gfp(nr_counters * counter_size,
+ __alignof__(*counters), gfp);
+ if (!counters) {
+ fbc[0].counters = NULL;
return -ENOMEM;
+ }

- debug_percpu_counter_activate(fbc);
+ for (i = 0; i < nr_counters; i++) {
+ raw_spin_lock_init(&fbc[i].lock);
+ lockdep_set_class(&fbc[i].lock, key);
+#ifdef CONFIG_HOTPLUG_CPU
+ INIT_LIST_HEAD(&fbc[i].list);
+#endif
+ fbc[i].count = amount;
+ fbc[i].counters = (void *)counters + (i * counter_size);
+
+ debug_percpu_counter_activate(&fbc[i]);
+ }

#ifdef CONFIG_HOTPLUG_CPU
- INIT_LIST_HEAD(&fbc->list);
spin_lock_irqsave(&percpu_counters_lock, flags);
- list_add(&fbc->list, &percpu_counters);
+ for (i = 0; i < nr_counters; i++)
+ list_add(&fbc[i].list, &percpu_counters);
spin_unlock_irqrestore(&percpu_counters_lock, flags);
#endif
return 0;
}
-EXPORT_SYMBOL(__percpu_counter_init);
+EXPORT_SYMBOL(__percpu_counter_init_many);

-void percpu_counter_destroy(struct percpu_counter *fbc)
+void percpu_counter_destroy_many(struct percpu_counter *fbc, u32 nr_counters)
{
unsigned long flags __maybe_unused;
+ u32 i;
+
+ if (WARN_ON_ONCE(!fbc))
+ return;

- if (!fbc->counters)
+ if (!fbc[0].counters)
return;

- debug_percpu_counter_deactivate(fbc);
+ for (i = 0; i < nr_counters; i++)
+ debug_percpu_counter_deactivate(&fbc[i]);

#ifdef CONFIG_HOTPLUG_CPU
spin_lock_irqsave(&percpu_counters_lock, flags);
- list_del(&fbc->list);
+ for (i = 0; i < nr_counters; i++)
+ list_del(&fbc[i].list);
spin_unlock_irqrestore(&percpu_counters_lock, flags);
#endif
- free_percpu(fbc->counters);
- fbc->counters = NULL;
+
+ free_percpu(fbc[0].counters);
+
+ for (i = 0; i < nr_counters; i++)
+ fbc[i].counters = NULL;
}
-EXPORT_SYMBOL(percpu_counter_destroy);
+EXPORT_SYMBOL(percpu_counter_destroy_many);

int percpu_counter_batch __read_mostly = 32;
EXPORT_SYMBOL(percpu_counter_batch);
--
2.41.0
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