mirror of
https://github.com/torvalds/linux.git
synced 2024-12-05 10:32:35 +00:00
1431996bf9
Though tmpfs does not need it, percpu_counter_limited_add() can be twice as useful if it works sensibly with negative amounts (subs) - typically decrements towards a limit of 0 or nearby: as suggested by Dave Chinner. And in the course of that reworking, skip the percpu counter sum if it is already obvious that the limit would be passed: as suggested by Tim Chen. Extend the comment above __percpu_counter_limited_add(), defining the behaviour with positive and negative amounts, allowing negative limits, but not bothering about overflow beyond S64_MAX. Link: https://lkml.kernel.org/r/8f86083b-c452-95d4-365b-f16a2e4ebcd4@google.com Signed-off-by: Hugh Dickins <hughd@google.com> Cc: Axel Rasmussen <axelrasmussen@google.com> Cc: Carlos Maiolino <cem@kernel.org> Cc: Christian Brauner <brauner@kernel.org> Cc: Chuck Lever <chuck.lever@oracle.com> Cc: Darrick J. Wong <djwong@kernel.org> Cc: Dave Chinner <dchinner@redhat.com> Cc: Jan Kara <jack@suse.cz> Cc: Johannes Weiner <hannes@cmpxchg.org> Cc: Matthew Wilcox (Oracle) <willy@infradead.org> Cc: Tim Chen <tim.c.chen@intel.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
374 lines
9.7 KiB
C
374 lines
9.7 KiB
C
// SPDX-License-Identifier: GPL-2.0
|
|
/*
|
|
* Fast batching percpu counters.
|
|
*/
|
|
|
|
#include <linux/percpu_counter.h>
|
|
#include <linux/mutex.h>
|
|
#include <linux/init.h>
|
|
#include <linux/cpu.h>
|
|
#include <linux/module.h>
|
|
#include <linux/debugobjects.h>
|
|
|
|
#ifdef CONFIG_HOTPLUG_CPU
|
|
static LIST_HEAD(percpu_counters);
|
|
static DEFINE_SPINLOCK(percpu_counters_lock);
|
|
#endif
|
|
|
|
#ifdef CONFIG_DEBUG_OBJECTS_PERCPU_COUNTER
|
|
|
|
static const struct debug_obj_descr percpu_counter_debug_descr;
|
|
|
|
static bool percpu_counter_fixup_free(void *addr, enum debug_obj_state state)
|
|
{
|
|
struct percpu_counter *fbc = addr;
|
|
|
|
switch (state) {
|
|
case ODEBUG_STATE_ACTIVE:
|
|
percpu_counter_destroy(fbc);
|
|
debug_object_free(fbc, &percpu_counter_debug_descr);
|
|
return true;
|
|
default:
|
|
return false;
|
|
}
|
|
}
|
|
|
|
static const struct debug_obj_descr percpu_counter_debug_descr = {
|
|
.name = "percpu_counter",
|
|
.fixup_free = percpu_counter_fixup_free,
|
|
};
|
|
|
|
static inline void debug_percpu_counter_activate(struct percpu_counter *fbc)
|
|
{
|
|
debug_object_init(fbc, &percpu_counter_debug_descr);
|
|
debug_object_activate(fbc, &percpu_counter_debug_descr);
|
|
}
|
|
|
|
static inline void debug_percpu_counter_deactivate(struct percpu_counter *fbc)
|
|
{
|
|
debug_object_deactivate(fbc, &percpu_counter_debug_descr);
|
|
debug_object_free(fbc, &percpu_counter_debug_descr);
|
|
}
|
|
|
|
#else /* CONFIG_DEBUG_OBJECTS_PERCPU_COUNTER */
|
|
static inline void debug_percpu_counter_activate(struct percpu_counter *fbc)
|
|
{ }
|
|
static inline void debug_percpu_counter_deactivate(struct percpu_counter *fbc)
|
|
{ }
|
|
#endif /* CONFIG_DEBUG_OBJECTS_PERCPU_COUNTER */
|
|
|
|
void percpu_counter_set(struct percpu_counter *fbc, s64 amount)
|
|
{
|
|
int cpu;
|
|
unsigned long flags;
|
|
|
|
raw_spin_lock_irqsave(&fbc->lock, flags);
|
|
for_each_possible_cpu(cpu) {
|
|
s32 *pcount = per_cpu_ptr(fbc->counters, cpu);
|
|
*pcount = 0;
|
|
}
|
|
fbc->count = amount;
|
|
raw_spin_unlock_irqrestore(&fbc->lock, flags);
|
|
}
|
|
EXPORT_SYMBOL(percpu_counter_set);
|
|
|
|
/*
|
|
* local_irq_save() is needed to make the function irq safe:
|
|
* - The slow path would be ok as protected by an irq-safe spinlock.
|
|
* - this_cpu_add would be ok as it is irq-safe by definition.
|
|
* But:
|
|
* The decision slow path/fast path and the actual update must be atomic, too.
|
|
* Otherwise a call in process context could check the current values and
|
|
* decide that the fast path can be used. If now an interrupt occurs before
|
|
* the this_cpu_add(), and the interrupt updates this_cpu(*fbc->counters),
|
|
* then the this_cpu_add() that is executed after the interrupt has completed
|
|
* can produce values larger than "batch" or even overflows.
|
|
*/
|
|
void percpu_counter_add_batch(struct percpu_counter *fbc, s64 amount, s32 batch)
|
|
{
|
|
s64 count;
|
|
unsigned long flags;
|
|
|
|
local_irq_save(flags);
|
|
count = __this_cpu_read(*fbc->counters) + amount;
|
|
if (abs(count) >= batch) {
|
|
raw_spin_lock(&fbc->lock);
|
|
fbc->count += count;
|
|
__this_cpu_sub(*fbc->counters, count - amount);
|
|
raw_spin_unlock(&fbc->lock);
|
|
} else {
|
|
this_cpu_add(*fbc->counters, amount);
|
|
}
|
|
local_irq_restore(flags);
|
|
}
|
|
EXPORT_SYMBOL(percpu_counter_add_batch);
|
|
|
|
/*
|
|
* For percpu_counter with a big batch, the devication of its count could
|
|
* be big, and there is requirement to reduce the deviation, like when the
|
|
* counter's batch could be runtime decreased to get a better accuracy,
|
|
* which can be achieved by running this sync function on each CPU.
|
|
*/
|
|
void percpu_counter_sync(struct percpu_counter *fbc)
|
|
{
|
|
unsigned long flags;
|
|
s64 count;
|
|
|
|
raw_spin_lock_irqsave(&fbc->lock, flags);
|
|
count = __this_cpu_read(*fbc->counters);
|
|
fbc->count += count;
|
|
__this_cpu_sub(*fbc->counters, count);
|
|
raw_spin_unlock_irqrestore(&fbc->lock, flags);
|
|
}
|
|
EXPORT_SYMBOL(percpu_counter_sync);
|
|
|
|
/*
|
|
* Add up all the per-cpu counts, return the result. This is a more accurate
|
|
* but much slower version of percpu_counter_read_positive().
|
|
*
|
|
* We use the cpu mask of (cpu_online_mask | cpu_dying_mask) to capture sums
|
|
* from CPUs that are in the process of being taken offline. Dying cpus have
|
|
* been removed from the online mask, but may not have had the hotplug dead
|
|
* notifier called to fold the percpu count back into the global counter sum.
|
|
* By including dying CPUs in the iteration mask, we avoid this race condition
|
|
* so __percpu_counter_sum() just does the right thing when CPUs are being taken
|
|
* offline.
|
|
*/
|
|
s64 __percpu_counter_sum(struct percpu_counter *fbc)
|
|
{
|
|
s64 ret;
|
|
int cpu;
|
|
unsigned long flags;
|
|
|
|
raw_spin_lock_irqsave(&fbc->lock, flags);
|
|
ret = fbc->count;
|
|
for_each_cpu_or(cpu, cpu_online_mask, cpu_dying_mask) {
|
|
s32 *pcount = per_cpu_ptr(fbc->counters, cpu);
|
|
ret += *pcount;
|
|
}
|
|
raw_spin_unlock_irqrestore(&fbc->lock, flags);
|
|
return ret;
|
|
}
|
|
EXPORT_SYMBOL(__percpu_counter_sum);
|
|
|
|
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;
|
|
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;
|
|
}
|
|
|
|
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
|
|
spin_lock_irqsave(&percpu_counters_lock, flags);
|
|
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_many);
|
|
|
|
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[0].counters)
|
|
return;
|
|
|
|
for (i = 0; i < nr_counters; i++)
|
|
debug_percpu_counter_deactivate(&fbc[i]);
|
|
|
|
#ifdef CONFIG_HOTPLUG_CPU
|
|
spin_lock_irqsave(&percpu_counters_lock, flags);
|
|
for (i = 0; i < nr_counters; i++)
|
|
list_del(&fbc[i].list);
|
|
spin_unlock_irqrestore(&percpu_counters_lock, flags);
|
|
#endif
|
|
|
|
free_percpu(fbc[0].counters);
|
|
|
|
for (i = 0; i < nr_counters; i++)
|
|
fbc[i].counters = NULL;
|
|
}
|
|
EXPORT_SYMBOL(percpu_counter_destroy_many);
|
|
|
|
int percpu_counter_batch __read_mostly = 32;
|
|
EXPORT_SYMBOL(percpu_counter_batch);
|
|
|
|
static int compute_batch_value(unsigned int cpu)
|
|
{
|
|
int nr = num_online_cpus();
|
|
|
|
percpu_counter_batch = max(32, nr*2);
|
|
return 0;
|
|
}
|
|
|
|
static int percpu_counter_cpu_dead(unsigned int cpu)
|
|
{
|
|
#ifdef CONFIG_HOTPLUG_CPU
|
|
struct percpu_counter *fbc;
|
|
|
|
compute_batch_value(cpu);
|
|
|
|
spin_lock_irq(&percpu_counters_lock);
|
|
list_for_each_entry(fbc, &percpu_counters, list) {
|
|
s32 *pcount;
|
|
|
|
raw_spin_lock(&fbc->lock);
|
|
pcount = per_cpu_ptr(fbc->counters, cpu);
|
|
fbc->count += *pcount;
|
|
*pcount = 0;
|
|
raw_spin_unlock(&fbc->lock);
|
|
}
|
|
spin_unlock_irq(&percpu_counters_lock);
|
|
#endif
|
|
return 0;
|
|
}
|
|
|
|
/*
|
|
* Compare counter against given value.
|
|
* Return 1 if greater, 0 if equal and -1 if less
|
|
*/
|
|
int __percpu_counter_compare(struct percpu_counter *fbc, s64 rhs, s32 batch)
|
|
{
|
|
s64 count;
|
|
|
|
count = percpu_counter_read(fbc);
|
|
/* Check to see if rough count will be sufficient for comparison */
|
|
if (abs(count - rhs) > (batch * num_online_cpus())) {
|
|
if (count > rhs)
|
|
return 1;
|
|
else
|
|
return -1;
|
|
}
|
|
/* Need to use precise count */
|
|
count = percpu_counter_sum(fbc);
|
|
if (count > rhs)
|
|
return 1;
|
|
else if (count < rhs)
|
|
return -1;
|
|
else
|
|
return 0;
|
|
}
|
|
EXPORT_SYMBOL(__percpu_counter_compare);
|
|
|
|
/*
|
|
* Compare counter, and add amount if total is: less than or equal to limit if
|
|
* amount is positive, or greater than or equal to limit if amount is negative.
|
|
* Return true if amount is added, or false if total would be beyond the limit.
|
|
*
|
|
* Negative limit is allowed, but unusual.
|
|
* When negative amounts (subs) are given to percpu_counter_limited_add(),
|
|
* the limit would most naturally be 0 - but other limits are also allowed.
|
|
*
|
|
* Overflow beyond S64_MAX is not allowed for: counter, limit and amount
|
|
* are all assumed to be sane (far from S64_MIN and S64_MAX).
|
|
*/
|
|
bool __percpu_counter_limited_add(struct percpu_counter *fbc,
|
|
s64 limit, s64 amount, s32 batch)
|
|
{
|
|
s64 count;
|
|
s64 unknown;
|
|
unsigned long flags;
|
|
bool good = false;
|
|
|
|
if (amount == 0)
|
|
return true;
|
|
|
|
local_irq_save(flags);
|
|
unknown = batch * num_online_cpus();
|
|
count = __this_cpu_read(*fbc->counters);
|
|
|
|
/* Skip taking the lock when safe */
|
|
if (abs(count + amount) <= batch &&
|
|
((amount > 0 && fbc->count + unknown <= limit) ||
|
|
(amount < 0 && fbc->count - unknown >= limit))) {
|
|
this_cpu_add(*fbc->counters, amount);
|
|
local_irq_restore(flags);
|
|
return true;
|
|
}
|
|
|
|
raw_spin_lock(&fbc->lock);
|
|
count = fbc->count + amount;
|
|
|
|
/* Skip percpu_counter_sum() when safe */
|
|
if (amount > 0) {
|
|
if (count - unknown > limit)
|
|
goto out;
|
|
if (count + unknown <= limit)
|
|
good = true;
|
|
} else {
|
|
if (count + unknown < limit)
|
|
goto out;
|
|
if (count - unknown >= limit)
|
|
good = true;
|
|
}
|
|
|
|
if (!good) {
|
|
s32 *pcount;
|
|
int cpu;
|
|
|
|
for_each_cpu_or(cpu, cpu_online_mask, cpu_dying_mask) {
|
|
pcount = per_cpu_ptr(fbc->counters, cpu);
|
|
count += *pcount;
|
|
}
|
|
if (amount > 0) {
|
|
if (count > limit)
|
|
goto out;
|
|
} else {
|
|
if (count < limit)
|
|
goto out;
|
|
}
|
|
good = true;
|
|
}
|
|
|
|
count = __this_cpu_read(*fbc->counters);
|
|
fbc->count += count + amount;
|
|
__this_cpu_sub(*fbc->counters, count);
|
|
out:
|
|
raw_spin_unlock(&fbc->lock);
|
|
local_irq_restore(flags);
|
|
return good;
|
|
}
|
|
|
|
static int __init percpu_counter_startup(void)
|
|
{
|
|
int ret;
|
|
|
|
ret = cpuhp_setup_state(CPUHP_AP_ONLINE_DYN, "lib/percpu_cnt:online",
|
|
compute_batch_value, NULL);
|
|
WARN_ON(ret < 0);
|
|
ret = cpuhp_setup_state_nocalls(CPUHP_PERCPU_CNT_DEAD,
|
|
"lib/percpu_cnt:dead", NULL,
|
|
percpu_counter_cpu_dead);
|
|
WARN_ON(ret < 0);
|
|
return 0;
|
|
}
|
|
module_init(percpu_counter_startup);
|