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bpf: Optimize rcu_barrier usage between hash map and bpf_mem_alloc.

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User space might be creating and destroying a lot of hash maps. Synchronous
rcu_barrier-s in a destruction path of hash map delay freeing of hash buckets
and other map memory and may cause artificial OOM situation under stress.
Optimize rcu_barrier usage between bpf hash map and bpf_mem_alloc:
- remove rcu_barrier from hash map, since htab doesn't use call_rcu
  directly and there are no callback to wait for.
- bpf_mem_alloc has call_rcu_in_progress flag that indicates pending callbacks.
  Use it to avoid barriers in fast path.
- When barriers are needed copy bpf_mem_alloc into temp structure
  and wait for rcu barrier-s in the worker to let the rest of
  hash map freeing to proceed.

Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20220902211058.60789-17-alexei.starovoitov@gmail.com
This commit is contained in:
Alexei Starovoitov 2022-09-02 14:10:58 -07:00 • committed by Daniel Borkmann
parent bfc03c15be
commit 9f2c6e96c6
3 changed files with 69 additions and 19 deletions
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2
include/linux/bpf_mem_alloc.h
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@ -3,6 +3,7 @@
#ifndef _BPF_MEM_ALLOC_H
#define _BPF_MEM_ALLOC_H
#include <linux/compiler_types.h>
#include <linux/workqueue.h>
struct bpf_mem_cache;
struct bpf_mem_caches;
@ -10,6 +11,7 @@ struct bpf_mem_caches;
struct bpf_mem_alloc {
struct bpf_mem_caches __percpu *caches;
struct bpf_mem_cache __percpu *cache;
struct work_struct work;
};
int bpf_mem_alloc_init(struct bpf_mem_alloc *ma, int size, bool percpu);