Commit 7c7982cb authored by Martin KaFai Lau's avatar Martin KaFai Lau Committed by Alexei Starovoitov
Browse files

bpf: sk_storage: Prefer to get a free cache_idx 



The cache_idx is currently picked by RR.  There is chance that
the same cache_idx will be picked by multiple sk_storage_maps while
other cache_idx is still unused.  e.g. It could happen when the
sk_storage_map is recreated during the restart of the user
space process.

This patch tracks the usage count for each cache_idx.  There is
16 of them now (defined in BPF_SK_STORAGE_CACHE_SIZE).
It will try to pick the free cache_idx.  If none was found,
it would pick one with the minimal usage count.

Signed-off-by: default avatarMartin KaFai Lau <kafai@fb.com>
Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
Acked-by: default avatarJohn Fastabend <john.fastabend@gmail.com>
Link: https://lore.kernel.org/bpf/20200617174226.2301909-1-kafai@fb.com
parent 7bd3a33a

net/core/bpf_sk_storage.c

+37 −4
Original line number Diff line number Diff line
@@ -11,8 +11,6 @@ 
#include <uapi/linux/sock_diag.h>

#include <uapi/linux/btf.h>



static atomic_t cache_idx;



#define SK_STORAGE_CREATE_FLAG_MASK					\

	(BPF_F_NO_PREALLOC | BPF_F_CLONE)
@@ -81,6 +79,9 @@ struct bpf_sk_storage_elem { 
#define SDATA(_SELEM) (&(_SELEM)->sdata)

#define BPF_SK_STORAGE_CACHE_SIZE	16



static DEFINE_SPINLOCK(cache_idx_lock);

static u64 cache_idx_usage_counts[BPF_SK_STORAGE_CACHE_SIZE];



struct bpf_sk_storage {

	struct bpf_sk_storage_data __rcu *cache[BPF_SK_STORAGE_CACHE_SIZE];

	struct hlist_head list;	/* List of bpf_sk_storage_elem */
@@ -512,6 +513,37 @@ static int sk_storage_delete(struct sock *sk, struct bpf_map *map) 
	return 0;

}



static u16 cache_idx_get(void)

{

	u64 min_usage = U64_MAX;

	u16 i, res = 0;



	spin_lock(&cache_idx_lock);



	for (i = 0; i < BPF_SK_STORAGE_CACHE_SIZE; i++) {

		if (cache_idx_usage_counts[i] < min_usage) {

			min_usage = cache_idx_usage_counts[i];

			res = i;



			/* Found a free cache_idx */

			if (!min_usage)

				break;

		}

	}

	cache_idx_usage_counts[res]++;



	spin_unlock(&cache_idx_lock);



	return res;

}



static void cache_idx_free(u16 idx)

{

	spin_lock(&cache_idx_lock);

	cache_idx_usage_counts[idx]--;

	spin_unlock(&cache_idx_lock);

}



/* Called by __sk_destruct() & bpf_sk_storage_clone() */

void bpf_sk_storage_free(struct sock *sk)

{
@@ -560,6 +592,8 @@ static void bpf_sk_storage_map_free(struct bpf_map *map) 


	smap = (struct bpf_sk_storage_map *)map;



	cache_idx_free(smap->cache_idx);



	/* Note that this map might be concurrently cloned from

	 * bpf_sk_storage_clone. Wait for any existing bpf_sk_storage_clone

	 * RCU read section to finish before proceeding. New RCU
@@ -673,8 +707,7 @@ static struct bpf_map *bpf_sk_storage_map_alloc(union bpf_attr *attr) 
	}



	smap->elem_size = sizeof(struct bpf_sk_storage_elem) + attr->value_size;

	smap->cache_idx = (unsigned int)atomic_inc_return(&cache_idx) %

		BPF_SK_STORAGE_CACHE_SIZE;

	smap->cache_idx = cache_idx_get();



	return &smap->map;

}

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