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Date: Sat, 9 Jan 2016 18:06:15 +0800
From: Ming Lei <tom.leiming@...il.com>
To: Martin KaFai Lau <kafai@...com>
Cc: Network Development <netdev@...r.kernel.org>,
Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
FB Kernel Team <kernel-team@...com>,
Alexei Starovoitov <alexei.starovoitov@...il.com>
Subject: Re: [PATCH net-next 2/4] bpf: bpf_htab: Add BPF_MAP_TYPE_PERCPU_HASH
On Fri, Jan 8, 2016 at 6:35 AM, Martin KaFai Lau <kafai@...com> wrote:
> This patch adds BPFMAP_TYPE_PERCPU_HASH map type and its
> htab_map_ops implementation.
>
> Signed-off-by: Martin KaFai Lau <kafai@...com>
> ---
> include/uapi/linux/bpf.h | 1 +
> kernel/bpf/hashtab.c | 201 ++++++++++++++++++++++++++++++++++++++++++++++-
> 2 files changed, 201 insertions(+), 1 deletion(-)
>
> diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
> index 8bed7f1..e4f8060 100644
> --- a/include/uapi/linux/bpf.h
> +++ b/include/uapi/linux/bpf.h
> @@ -81,6 +81,7 @@ enum bpf_map_type {
> BPF_MAP_TYPE_ARRAY,
> BPF_MAP_TYPE_PROG_ARRAY,
> BPF_MAP_TYPE_PERF_EVENT_ARRAY,
> + BPF_MAP_TYPE_PERCPU_HASH,
> };
>
> enum bpf_prog_type {
> diff --git a/kernel/bpf/hashtab.c b/kernel/bpf/hashtab.c
> index d55df8c..63f2945 100644
> --- a/kernel/bpf/hashtab.c
> +++ b/kernel/bpf/hashtab.c
> @@ -278,7 +278,7 @@ find_first_elem:
> }
>
> static struct htab_elem_common *htab_elem_common_alloc(struct bpf_htab *htab,
> - void *key)
> + void *key)
better to not introduce the above change.
> {
> struct htab_elem_common *l;
>
> @@ -451,9 +451,208 @@ static struct bpf_map_type_list htab_type __read_mostly = {
> .type = BPF_MAP_TYPE_HASH,
> };
>
> +/* each htab_percpu_elem is struct htab_percpu_elem + key */
> +struct htab_percpu_elem {
> + struct htab_elem_common common;
> + void * __percpu value;
> + char key[0] __aligned(8);
> +};
> +
> +static struct htab_percpu_elem *htab_percpu_elem(struct htab_elem_common *l)
> +{
> + return (struct htab_percpu_elem *)l;
> +}
> +
> +static void htab_percpu_elem_free(struct htab_percpu_elem *l)
> +{
> + free_percpu(l->value);
> + kfree(l);
> +}
> +
> +static void htab_percpu_elem_rcu_free(struct rcu_head *head)
> +{
> + struct htab_elem_common *l = container_of(head,
> + struct htab_elem_common,
> + rcu);
> +
> + htab_percpu_elem_free(htab_percpu_elem(l));
> +}
> +
> +static void htab_percpu_map_flush(struct bpf_htab *htab)
> +{
> + int i;
> +
> + for (i = 0; i < htab->n_buckets; i++) {
> + struct hlist_head *head = select_bucket(htab, i);
> + struct hlist_node *n;
> + struct htab_elem_common *l;
> +
> + hlist_for_each_entry_safe(l, n, head, hash_node) {
> + hlist_del_rcu(&l->hash_node);
> + atomic_dec(&htab->count);
> + htab_percpu_elem_free(htab_percpu_elem(l));
> + }
> + }
> +}
The above helper should have been saved by introduce percpu_map
flag in bpf_htab.
> +
> +/* Called from syscall */
> +static struct bpf_map *htab_percpu_map_alloc(union bpf_attr *attr)
> +{
> + u32 elem_size = sizeof(struct htab_percpu_elem) +
> + round_up(attr->key_size, 8);
> + u32 elem_value_size = elem_size +
> + num_possible_cpus() * attr->value_size;
> +
> + return __htab_map_alloc(attr, elem_size, elem_value_size,
> + offsetof(struct htab_percpu_elem, key),
> + htab_percpu_map_flush);
> +}
> +
> +/* Called from syscall or from eBPF program */
> +static int htab_percpu_map_delete_elem(struct bpf_map *map, void *key)
> +{
> + struct bpf_htab *htab = container_of(map, struct bpf_htab, map);
> + struct htab_elem_common *l;
> + struct hlist_head *head;
> + unsigned long flags;
> + u32 hash, key_size;
> + struct bucket *b;
> + int ret = -ENOENT;
> +
> + WARN_ON_ONCE(!rcu_read_lock_held());
> +
> + key_size = map->key_size;
> +
> + hash = htab_map_hash(key, key_size);
> + b = __select_bucket(htab, hash);
> + head = &b->head;
> +
> + raw_spin_lock_irqsave(&b->lock, flags);
> +
> + l = lookup_elem_raw(htab, head, hash, key);
> +
> + if (l) {
> + hlist_del_rcu(&l->hash_node);
> + atomic_dec(&htab->count);
> + call_rcu(&l->rcu, htab_percpu_elem_rcu_free);
> + ret = 0;
> + }
> +
> + raw_spin_unlock_irqrestore(&b->lock, flags);
> + return ret;
> +}
> +
> +/* Called from syscall or eBPF program */
> +static void *htab_percpu_map_lookup_elem(struct bpf_map *map, void *key)
> +{
> + struct bpf_htab *htab = container_of(map, struct bpf_htab, map);
> + struct htab_elem_common *l;
> +
> + l = __htab_map_lookup_elem(htab, key);
> + if (l) {
> + void *value = per_cpu_ptr(htab_percpu_elem(l)->value,
> + smp_processor_id());
> + return value;
> + }
> +
> + return NULL;
> +
> +}
> +
> +/* Called from syscall or from eBPF program */
> +static int htab_percpu_map_update_elem(struct bpf_map *map, void *key,
> + void *value, u64 map_flags)
> +{
> + struct bpf_htab *htab = container_of(map, struct bpf_htab, map);
> + struct htab_percpu_elem *l_new, *l_old;
> + struct hlist_head *head;
> + struct bucket *b;
> + unsigned long flags;
> + int ret;
> +
> + if (map_flags > BPF_EXIST)
> + /* unknown flags */
> + return -EINVAL;
> +
> + WARN_ON_ONCE(!rcu_read_lock_held());
> +
> + /* allocate new element outside of lock */
> + l_new = htab_percpu_elem(htab_elem_common_alloc(htab, key));
> + if (!l_new)
> + return -ENOMEM;
> +
> + l_new->value = __alloc_percpu_gfp(htab->map.value_size, 8,
> + GFP_ATOMIC | __GFP_NOWARN);
Looks not good to introduce another memory allocation in eBPF prog,
it is a bit heavy to run, and it is in my TODO list to remove allocation of
htab_elem in eBPF prog.
> + if (!l_new->value) {
> + htab_percpu_elem_free(l_new);
> + return -ENOMEM;
> + }
> +
> + memcpy(raw_cpu_ptr(l_new->value), value, map->value_size);
> +
> + b = __select_bucket(htab, l_new->common.hash);
> + head = &b->head;
> +
> + /* bpf_map_update_elem() can be called in_irq() */
> + raw_spin_lock_irqsave(&b->lock, flags);
> +
> + l_old = htab_percpu_elem(lookup_elem_raw(htab, head, l_new->common.hash,
> + key));
> +
> + if (!l_old && unlikely(atomic_read(&htab->count) >= map->max_entries)) {
> + /* if elem with this 'key' doesn't exist and we've reached
> + * max_entries limit, fail insertion of new elem
> + */
> + ret = -E2BIG;
> + goto err;
> + }
> +
> + if (l_old && map_flags == BPF_NOEXIST) {
> + /* elem already exists */
> + ret = -EEXIST;
> + goto err;
> + }
> +
> + if (!l_old && map_flags == BPF_EXIST) {
> + /* elem doesn't exist, cannot update it */
> + ret = -ENOENT;
> + goto err;
> + }
> +
> + if (l_old) {
> + memcpy(this_cpu_ptr(l_old->value), value, map->value_size);
> + } else {
> + hlist_add_head_rcu(&l_new->common.hash_node, head);
> + atomic_inc(&htab->count);
> + }
> +
> + raw_spin_unlock_irqrestore(&b->lock, flags);
> +
> + return 0;
> +err:
> + raw_spin_unlock_irqrestore(&b->lock, flags);
> + htab_percpu_elem_free(l_new);
> + return ret;
> +}
It isn't good to introduce so much code duplication.
> +
> +static const struct bpf_map_ops htab_percpu_ops = {
> + .map_alloc = htab_percpu_map_alloc,
> + .map_free = htab_map_free,
> + .map_get_next_key = htab_map_get_next_key,
> + .map_lookup_elem = htab_percpu_map_lookup_elem,
> + .map_update_elem = htab_percpu_map_update_elem,
> + .map_delete_elem = htab_percpu_map_delete_elem,
> +};
> +
> +static struct bpf_map_type_list htab_percpu_type __read_mostly = {
> + .ops = &htab_percpu_ops,
> + .type = BPF_MAP_TYPE_PERCPU_HASH,
> +};
> +
> static int __init register_htab_map(void)
> {
> bpf_register_map_type(&htab_type);
> + bpf_register_map_type(&htab_percpu_type);
> return 0;
> }
> late_initcall(register_htab_map);
> --
> 2.5.1
>
--
Ming Lei
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