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debugobjects: Add percpu free pools

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When a multi-threaded workload does a lot of small memory object
allocations and deallocations, it may cause the allocation and freeing of
many debug objects. This will make the global pool_lock a bottleneck in the
performance of the workload.  Since interrupts are disabled when acquiring
the pool_lock, it may even cause hard lockups to happen.

To reduce contention of the global pool_lock, add a percpu debug object
free pool that can be used to buffer some of the debug object allocation
and freeing requests without acquiring the pool_lock.  Each CPU will now
have a percpu free pool that can hold up to a maximum of 64 debug
objects. Allocation and freeing requests will go to the percpu free pool
first. If that fails, the pool_lock will be taken and the global free pool
will be used.

The presence or absence of obj_cache is used as a marker to see if the
percpu cache should be used.

Signed-off-by: Waiman Long <longman@redhat.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Yang Shi <yang.shi@linux.alibaba.com>
Cc: "Joel Fernandes (Google)" <joel@joelfernandes.org>
Cc: Qian Cai <cai@gmx.us>
Cc: Zhong Jiang <zhongjiang@huawei.com>
Link: https://lkml.kernel.org/r/20190520141450.7575-2-longman@redhat.com
This commit is contained in:
Waiman Long 2019-05-20 10:14:46 -04:00 committed by Thomas Gleixner
parent fecb0d95cd
commit d86998b17a
1 changed files with 91 additions and 24 deletions
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115
lib/debugobjects.c
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@ -25,6 +25,7 @@
#define ODEBUG_POOL_SIZE 1024
#define ODEBUG_POOL_MIN_LEVEL 256
#define ODEBUG_POOL_PERCPU_SIZE 64
#define ODEBUG_CHUNK_SHIFT PAGE_SHIFT
#define ODEBUG_CHUNK_SIZE (1 << ODEBUG_CHUNK_SHIFT)
@ -35,6 +36,17 @@ struct debug_bucket {
raw_spinlock_t lock;
};
/*
* Debug object percpu free list
* Access is protected by disabling irq
*/
struct debug_percpu_free {
struct hlist_head free_objs;
int obj_free;
};
static DEFINE_PER_CPU(struct debug_percpu_free, percpu_obj_pool);
static struct debug_bucket obj_hash[ODEBUG_HASH_SIZE];
static struct debug_obj obj_static_pool[ODEBUG_POOL_SIZE] __initdata;
@ -44,13 +56,19 @@ static DEFINE_RAW_SPINLOCK(pool_lock);
static HLIST_HEAD(obj_pool);
static HLIST_HEAD(obj_to_free);
/*
* Because of the presence of percpu free pools, obj_pool_free will
* under-count those in the percpu free pools. Similarly, obj_pool_used
* will over-count those in the percpu free pools. Adjustments will be
* made at debug_stats_show(). Both obj_pool_min_free and obj_pool_max_used
* can be off.
*/
static int obj_pool_min_free = ODEBUG_POOL_SIZE;
static int obj_pool_free = ODEBUG_POOL_SIZE;
static int obj_pool_used;
static int obj_pool_max_used;
/* The number of objs on the global free list */
static int obj_nr_tofree;
static struct kmem_cache *obj_cache;
static int debug_objects_maxchain __read_mostly;
static int __maybe_unused debug_objects_maxchecked __read_mostly;
@ -63,6 +81,7 @@ static int debug_objects_pool_size __read_mostly
static int debug_objects_pool_min_level __read_mostly
= ODEBUG_POOL_MIN_LEVEL;
static struct debug_obj_descr *descr_test __read_mostly;
static struct kmem_cache *obj_cache __read_mostly;
/*
* Track numbers of kmem_cache_alloc()/free() calls done.
@ -162,6 +181,21 @@ static struct debug_obj *lookup_object(void *addr, struct debug_bucket *b)
return NULL;
}
/*
* Allocate a new object from the hlist
*/
static struct debug_obj *__alloc_object(struct hlist_head *list)
{
struct debug_obj *obj = NULL;
if (list->first) {
obj = hlist_entry(list->first, typeof(*obj), node);
hlist_del(&obj->node);
}
return obj;
}
/*
* Allocate a new object. If the pool is empty, switch off the debugger.
* Must be called with interrupts disabled.
@ -169,20 +203,21 @@ static struct debug_obj *lookup_object(void *addr, struct debug_bucket *b)
static struct debug_obj *
alloc_object(void *addr, struct debug_bucket *b, struct debug_obj_descr *descr)
{
struct debug_obj *obj = NULL;
struct debug_percpu_free *percpu_pool;
struct debug_obj *obj;
if (likely(obj_cache)) {
percpu_pool = this_cpu_ptr(&percpu_obj_pool);
obj = __alloc_object(&percpu_pool->free_objs);
if (obj) {
percpu_pool->obj_free--;
goto init_obj;
}
}
raw_spin_lock(&pool_lock);
if (obj_pool.first) {
obj = hlist_entry(obj_pool.first, typeof(*obj), node);
obj->object = addr;
obj->descr = descr;
obj->state = ODEBUG_STATE_NONE;
obj->astate = 0;
hlist_del(&obj->node);
hlist_add_head(&obj->node, &b->list);
obj = __alloc_object(&obj_pool);
if (obj) {
obj_pool_used++;
if (obj_pool_used > obj_pool_max_used)
obj_pool_max_used = obj_pool_used;
@ -193,6 +228,14 @@ alloc_object(void *addr, struct debug_bucket *b, struct debug_obj_descr *descr)
}
raw_spin_unlock(&pool_lock);
init_obj:
if (obj) {
obj->object = addr;
obj->descr = descr;
obj->state = ODEBUG_STATE_NONE;
obj->astate = 0;
hlist_add_head(&obj->node, &b->list);
}
return obj;
}
@ -247,8 +290,21 @@ static bool __free_object(struct debug_obj *obj)
{
unsigned long flags;
bool work;
struct debug_percpu_free *percpu_pool;
raw_spin_lock_irqsave(&pool_lock, flags);
local_irq_save(flags);
/*
* Try to free it into the percpu pool first.
*/
percpu_pool = this_cpu_ptr(&percpu_obj_pool);
if (obj_cache && percpu_pool->obj_free < ODEBUG_POOL_PERCPU_SIZE) {
hlist_add_head(&obj->node, &percpu_pool->free_objs);
percpu_pool->obj_free++;
local_irq_restore(flags);
return false;
}
raw_spin_lock(&pool_lock);
work = (obj_pool_free > debug_objects_pool_size) && obj_cache;
obj_pool_used--;
@ -259,7 +315,8 @@ static bool __free_object(struct debug_obj *obj)
obj_pool_free++;
hlist_add_head(&obj->node, &obj_pool);
}
raw_spin_unlock_irqrestore(&pool_lock, flags);
raw_spin_unlock(&pool_lock);
local_irq_restore(flags);
return work;
}
@ -822,13 +879,19 @@ void debug_check_no_obj_freed(const void *address, unsigned long size)
static int debug_stats_show(struct seq_file *m, void *v)
{
int cpu, obj_percpu_free = 0;
for_each_possible_cpu(cpu)
obj_percpu_free += per_cpu(percpu_obj_pool.obj_free, cpu);
seq_printf(m, "max_chain :%d\n", debug_objects_maxchain);
seq_printf(m, "max_checked :%d\n", debug_objects_maxchecked);
seq_printf(m, "warnings :%d\n", debug_objects_warnings);
seq_printf(m, "fixups :%d\n", debug_objects_fixups);
seq_printf(m, "pool_free :%d\n", obj_pool_free);
seq_printf(m, "pool_free :%d\n", obj_pool_free + obj_percpu_free);
seq_printf(m, "pool_pcp_free :%d\n", obj_percpu_free);
seq_printf(m, "pool_min_free :%d\n", obj_pool_min_free);
seq_printf(m, "pool_used :%d\n", obj_pool_used);
seq_printf(m, "pool_used :%d\n", obj_pool_used - obj_percpu_free);
seq_printf(m, "pool_max_used :%d\n", obj_pool_max_used);
seq_printf(m, "on_free_list :%d\n", obj_nr_tofree);
seq_printf(m, "objs_allocated:%d\n", debug_objects_allocated);
@ -1165,9 +1228,20 @@ free:
*/
void __init debug_objects_mem_init(void)
{
int cpu;
if (!debug_objects_enabled)
return;
/*
* Initialize the percpu object pools
*
* Initialization is not strictly necessary, but was done for
* completeness.
*/
for_each_possible_cpu(cpu)
INIT_HLIST_HEAD(&per_cpu(percpu_obj_pool.free_objs, cpu));
obj_cache = kmem_cache_create("debug_objects_cache",
sizeof (struct debug_obj), 0,
SLAB_DEBUG_OBJECTS | SLAB_NOLEAKTRACE,
@ -1179,11 +1253,4 @@ void __init debug_objects_mem_init(void)
pr_warn("out of memory.\n");
} else
debug_objects_selftest();
/*
* Increase the thresholds for allocating and freeing objects
* according to the number of possible CPUs available in the system.
*/
debug_objects_pool_size += num_possible_cpus() * 32;
debug_objects_pool_min_level += num_possible_cpus() * 4;
}