From: Waiman Long longman@redhat.com
[ Upstream commit d86998b17a01050c0232231fa481e65ef8171ca6 ]
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 Stable-dep-of: 63a759694eed ("debugobject: Prevent init race with static objects") Signed-off-by: Sasha Levin sashal@kernel.org --- lib/debugobjects.c | 115 +++++++++++++++++++++++++++++++++++---------- 1 file changed, 91 insertions(+), 24 deletions(-)
diff --git a/lib/debugobjects.c b/lib/debugobjects.c index 14afeeb7d6ef5..6e2baf9e9eb27 100644 --- a/lib/debugobjects.c +++ b/lib/debugobjects.c @@ -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; - - 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); + struct debug_percpu_free *percpu_pool; + struct debug_obj *obj;
- hlist_add_head(&obj->node, &b->list); + 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); + 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); @@ -1177,9 +1240,20 @@ static int __init debug_objects_replace_static_objects(void) */ 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, @@ -1191,11 +1265,4 @@ 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; }