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bpf: Reuse freed element in free_by_rcu during allocation

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When there are batched freeing operations on a specific CPU, part of
the freed elements ((high_watermark - lower_watermark) / 2 + 1) will be
indirectly moved into waiting_for_gp list through free_by_rcu list.
After call_rcu_in_progress becomes false again, the remaining elements
in free_by_rcu list will be moved to waiting_for_gp list by the next
invocation of free_bulk(). However if the expiration of RCU tasks trace
grace period is relatively slow, none element in free_by_rcu list will
be moved.

So instead of invoking __alloc_percpu_gfp() or kmalloc_node() to
allocate a new object, in alloc_bulk() just check whether or not there is
freed element in free_by_rcu list and reuse it if available.

Acked-by: Yonghong Song <yhs@fb.com>
Signed-off-by: Hou Tao <houtao1@huawei.com>
Link: https://lore.kernel.org/r/20221209010947.3130477-2-houtao@huaweicloud.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
This commit is contained in:
Hou Tao 2022-12-09 09:09:46 +08:00 committed by Alexei Starovoitov
parent e60db051a4
commit 0893d6007d
1 changed files with 18 additions and 3 deletions
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21
kernel/bpf/memalloc.c
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@ -171,9 +171,24 @@ static void alloc_bulk(struct bpf_mem_cache *c, int cnt, int node)
memcg = get_memcg(c);
old_memcg = set_active_memcg(memcg);
for (i = 0; i < cnt; i++) {
obj = __alloc(c, node);
if (!obj)
break;
/*
* free_by_rcu is only manipulated by irq work refill_work().
* IRQ works on the same CPU are called sequentially, so it is
* safe to use __llist_del_first() here. If alloc_bulk() is
* invoked by the initial prefill, there will be no running
* refill_work(), so __llist_del_first() is fine as well.
*
* In most cases, objects on free_by_rcu are from the same CPU.
* If some objects come from other CPUs, it doesn't incur any
* harm because NUMA_NO_NODE means the preference for current
* numa node and it is not a guarantee.
*/
obj = __llist_del_first(&c->free_by_rcu);
if (!obj) {
obj = __alloc(c, node);
if (!obj)
break;
}
if (IS_ENABLED(CONFIG_PREEMPT_RT))
/* In RT irq_work runs in per-cpu kthread, so disable
* interrupts to avoid preemption and interrupts and