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debugobjects: Track object usage to avoid premature freeing of objects

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The freelist is freed at a constant rate independent of the actual usage
requirements. That's bad in scenarios where usage comes in bursts. The end
of a burst puts the objects on the free list and freeing proceeds even when
the next burst which requires objects started again.

Keep track of the usage with a exponentially wheighted moving average and
take that into account in the worker function which frees objects from the
free list.

This further reduces the kmem_cache allocation/free rate for a full kernel
compile:

   	    kmem_cache_alloc()	kmem_cache_free()
Baseline:   225k		173k
Usage:	    170k		117k

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Zhen Lei <thunder.leizhen@huawei.com>
Link: https://lore.kernel.org/all/87bjznhme2.ffs@tglx
This commit is contained in:
Thomas Gleixner 2024-10-13 20:45:57 +02:00
parent 13f9ca7239
commit ff8d523cc4
1 changed files with 40 additions and 5 deletions
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45
lib/debugobjects.c
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@ -13,6 +13,7 @@
#include <linux/hash.h>
#include <linux/kmemleak.h>
#include <linux/sched.h>
#include <linux/sched/loadavg.h>
#include <linux/sched/task_stack.h>
#include <linux/seq_file.h>
#include <linux/slab.h>
@ -86,6 +87,7 @@ static struct obj_pool pool_to_free = {
static HLIST_HEAD(pool_boot);
static unsigned long avg_usage;
static bool obj_freeing;
static int __data_racy debug_objects_maxchain __read_mostly;
@ -427,11 +429,31 @@ static struct debug_obj *lookup_object(void *addr, struct debug_bucket *b)
return NULL;
}
static void calc_usage(void)
{
static DEFINE_RAW_SPINLOCK(avg_lock);
static unsigned long avg_period;
unsigned long cur, now = jiffies;
if (!time_after_eq(now, READ_ONCE(avg_period)))
return;
if (!raw_spin_trylock(&avg_lock))
return;
WRITE_ONCE(avg_period, now + msecs_to_jiffies(10));
cur = READ_ONCE(pool_global.stats.cur_used) * ODEBUG_FREE_WORK_MAX;
WRITE_ONCE(avg_usage, calc_load(avg_usage, EXP_5, cur));
raw_spin_unlock(&avg_lock);
}
static struct debug_obj *alloc_object(void *addr, struct debug_bucket *b,
const struct debug_obj_descr *descr)
{
struct debug_obj *obj;
calc_usage();
if (static_branch_likely(&obj_cache_enabled))
obj = pcpu_alloc();
else
@ -450,14 +472,26 @@ static struct debug_obj *alloc_object(void *addr, struct debug_bucket *b,
/* workqueue function to free objects. */
static void free_obj_work(struct work_struct *work)
{
bool free = true;
static unsigned long last_use_avg;
unsigned long cur_used, last_used, delta;
unsigned int max_free = 0;
WRITE_ONCE(obj_freeing, false);
/* Rate limit freeing based on current use average */
cur_used = READ_ONCE(avg_usage);
last_used = last_use_avg;
last_use_avg = cur_used;
if (!pool_count(&pool_to_free))
return;
for (unsigned int cnt = 0; cnt < ODEBUG_FREE_WORK_MAX; cnt++) {
if (cur_used <= last_used) {
delta = (last_used - cur_used) / ODEBUG_FREE_WORK_MAX;
max_free = min(delta, ODEBUG_FREE_WORK_MAX);
}
for (int cnt = 0; cnt < ODEBUG_FREE_WORK_MAX; cnt++) {
HLIST_HEAD(tofree);
/* Acquire and drop the lock for each batch */
@ -468,9 +502,10 @@ static void free_obj_work(struct work_struct *work)
/* Refill the global pool if possible */
if (pool_move_batch(&pool_global, &pool_to_free)) {
/* Don't free as there seems to be demand */
free = false;
} else if (free) {
max_free = 0;
} else if (max_free) {
pool_pop_batch(&tofree, &pool_to_free);
max_free--;
} else {
return;
}
@ -1110,7 +1145,7 @@ static int debug_stats_show(struct seq_file *m, void *v)
for_each_possible_cpu(cpu)
pcp_free += per_cpu(pool_pcpu.cnt, cpu);
pool_used = data_race(pool_global.stats.cur_used);
pool_used = READ_ONCE(pool_global.stats.cur_used);
pcp_free = min(pool_used, pcp_free);
pool_used -= pcp_free;