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bpf: Batch call_rcu callbacks instead of SLAB_TYPESAFE_BY_RCU.

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SLAB_TYPESAFE_BY_RCU makes kmem_caches non mergeable and slows down
kmem_cache_destroy. All bpf_mem_cache are safe to share across different maps
and programs. Convert SLAB_TYPESAFE_BY_RCU to batched call_rcu. This change
solves the memory consumption issue, avoids kmem_cache_destroy latency and
keeps bpf hash map performance the same.

Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Acked-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20220902211058.60789-10-alexei.starovoitov@gmail.com
This commit is contained in:
Alexei Starovoitov 2022-09-02 14:10:51 -07:00 committed by Daniel Borkmann
parent 7c266178aa
commit 8d5a8011b3
2 changed files with 66 additions and 4 deletions
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65
kernel/bpf/memalloc.c
View File

@ -101,6 +101,11 @@ struct bpf_mem_cache {
/* count of objects in free_llist */
int free_cnt;
int low_watermark, high_watermark, batch;
struct rcu_head rcu;
struct llist_head free_by_rcu;
struct llist_head waiting_for_gp;
atomic_t call_rcu_in_progress;
};
struct bpf_mem_caches {
@ -194,6 +199,45 @@ static void free_one(struct bpf_mem_cache *c, void *obj)
kfree(obj);
}
static void __free_rcu(struct rcu_head *head)
{
struct bpf_mem_cache *c = container_of(head, struct bpf_mem_cache, rcu);
struct llist_node *llnode = llist_del_all(&c->waiting_for_gp);
struct llist_node *pos, *t;
llist_for_each_safe(pos, t, llnode)
free_one(c, pos);
atomic_set(&c->call_rcu_in_progress, 0);
}
static void enque_to_free(struct bpf_mem_cache *c, void *obj)
{
struct llist_node *llnode = obj;
/* bpf_mem_cache is a per-cpu object. Freeing happens in irq_work.
* Nothing races to add to free_by_rcu list.
*/
__llist_add(llnode, &c->free_by_rcu);
}
static void do_call_rcu(struct bpf_mem_cache *c)
{
struct llist_node *llnode, *t;
if (atomic_xchg(&c->call_rcu_in_progress, 1))
return;
WARN_ON_ONCE(!llist_empty(&c->waiting_for_gp));
llist_for_each_safe(llnode, t, __llist_del_all(&c->free_by_rcu))
/* There is no concurrent __llist_add(waiting_for_gp) access.
* It doesn't race with llist_del_all either.
* But there could be two concurrent llist_del_all(waiting_for_gp):
* from __free_rcu() and from drain_mem_cache().
*/
__llist_add(llnode, &c->waiting_for_gp);
call_rcu(&c->rcu, __free_rcu);
}
static void free_bulk(struct bpf_mem_cache *c)
{
struct llist_node *llnode, *t;
@ -212,12 +256,13 @@ static void free_bulk(struct bpf_mem_cache *c)
local_dec(&c->active);
if (IS_ENABLED(CONFIG_PREEMPT_RT))
local_irq_restore(flags);
free_one(c, llnode);
enque_to_free(c, llnode);
} while (cnt > (c->high_watermark + c->low_watermark) / 2);
/* and drain free_llist_extra */
llist_for_each_safe(llnode, t, llist_del_all(&c->free_llist_extra))
free_one(c, llnode);
enque_to_free(c, llnode);
do_call_rcu(c);
}
static void bpf_mem_refill(struct irq_work *work)
@ -303,7 +348,7 @@ int bpf_mem_alloc_init(struct bpf_mem_alloc *ma, int size)
return -ENOMEM;
size += LLIST_NODE_SZ; /* room for llist_node */
snprintf(buf, sizeof(buf), "bpf-%u", size);
kmem_cache = kmem_cache_create(buf, size, 8, SLAB_TYPESAFE_BY_RCU, NULL);
kmem_cache = kmem_cache_create(buf, size, 8, 0, NULL);
if (!kmem_cache) {
free_percpu(pc);
return -ENOMEM;
@ -345,6 +390,15 @@ static void drain_mem_cache(struct bpf_mem_cache *c)
{
struct llist_node *llnode, *t;
/* The caller has done rcu_barrier() and no progs are using this
* bpf_mem_cache, but htab_map_free() called bpf_mem_cache_free() for
* all remaining elements and they can be in free_by_rcu or in
* waiting_for_gp lists, so drain those lists now.
*/
llist_for_each_safe(llnode, t, __llist_del_all(&c->free_by_rcu))
free_one(c, llnode);
llist_for_each_safe(llnode, t, llist_del_all(&c->waiting_for_gp))
free_one(c, llnode);
llist_for_each_safe(llnode, t, llist_del_all(&c->free_llist))
free_one(c, llnode);
llist_for_each_safe(llnode, t, llist_del_all(&c->free_llist_extra))
@ -366,6 +420,10 @@ void bpf_mem_alloc_destroy(struct bpf_mem_alloc *ma)
kmem_cache_destroy(c->kmem_cache);
if (c->objcg)
obj_cgroup_put(c->objcg);
/* c->waiting_for_gp list was drained, but __free_rcu might
* still execute. Wait for it now before we free 'c'.
*/
rcu_barrier();
free_percpu(ma->cache);
ma->cache = NULL;
}
@ -379,6 +437,7 @@ void bpf_mem_alloc_destroy(struct bpf_mem_alloc *ma)
}
if (c->objcg)
obj_cgroup_put(c->objcg);
rcu_barrier();
free_percpu(ma->caches);
ma->caches = NULL;
}

5
kernel/bpf/syscall.c
View File

@ -638,7 +638,10 @@ static void __bpf_map_put(struct bpf_map *map, bool do_idr_lock)
bpf_map_free_id(map, do_idr_lock);
btf_put(map->btf);
INIT_WORK(&map->work, bpf_map_free_deferred);
schedule_work(&map->work);
/* Avoid spawning kworkers, since they all might contend
* for the same mutex like slab_mutex.
*/
queue_work(system_unbound_wq, &map->work);
}
}