Re: [bpf-next V5 PATCH 10/15] xdp: rhashtable with allocator ID to pointer mapping

Alexander Duyck
2018-03-23T16:56:52Z

On Fri, Mar 23, 2018 at 5:18 AM, Jesper Dangaard Brouer
<brouer@redhat.com> wrote:
> Use the IDA infrastructure for getting a cyclic increasing ID number,
> that is used for keeping track of each registered allocator per
> RX-queue xdp_rxq_info. Instead of using the IDR infrastructure, which
> uses a radix tree, use a dynamic rhashtable, for creating ID to
> pointer lookup table, because this is faster.
>
> The problem that is being solved here is that, the xdp_rxq_info
> pointer (stored in xdp_buff) cannot be used directly, as the
> guaranteed lifetime is too short. The info is needed on a
> (potentially) remote CPU during DMA-TX completion time . In an
> xdp_frame the xdp_mem_info is stored, when it got converted from an
> xdp_buff, which is sufficient for the simple page refcnt based recycle
> schemes.
>
> For more advanced allocators there is a need to store a pointer to the
> registered allocator. Thus, there is a need to guard the lifetime or
> validity of the allocator pointer, which is done through this
> rhashtable ID map to pointer. The removal and validity of of the
> allocator and helper struct xdp_mem_allocator is guarded by RCU. The
> allocator will be created by the driver, and registered with
> xdp_rxq_info_reg_mem_model().
>
> It is up-to debate who is responsible for freeing the allocator
> pointer or invoking the allocator destructor function. In any case,
> this must happen via RCU freeing.
>
> Use the IDA infrastructure for getting a cyclic increasing ID number,
> that is used for keeping track of each registered allocator per
> RX-queue xdp_rxq_info.
>
> V4: Per req of Jason Wang
> - Use xdp_rxq_info_reg_mem_model() in all drivers implementing
> XDP_REDIRECT, even-though it's not strictly necessary when
> allocator==NULL for type MEM_TYPE_PAGE_SHARED (given it's zero).
>
> Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>
> ---
> drivers/net/ethernet/intel/ixgbe/ixgbe_main.c | 9 +
> drivers/net/tun.c | 6 +
> drivers/net/virtio_net.c | 7 +
> include/net/xdp.h | 15 --
> net/core/xdp.c | 230 ++++++++++++++++++++++++-
> 5 files changed, 248 insertions(+), 19 deletions(-)
>
> diff --git a/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c b/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c
> index 45520eb503ee..ff069597fccf 100644
> --- a/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c
> +++ b/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c
> @@ -6360,7 +6360,7 @@ int ixgbe_setup_rx_resources(struct ixgbe_adapter *adapter,
> struct device *dev = rx_ring->dev;
> int orig_node = dev_to_node(dev);
> int ring_node = -1;
> - int size;
> + int size, err;
>
> size = sizeof(struct ixgbe_rx_buffer) * rx_ring->count;
>
> @@ -6397,6 +6397,13 @@ int ixgbe_setup_rx_resources(struct ixgbe_adapter *adapter,
> rx_ring->queue_index) < 0)
> goto err;
>
> + err = xdp_rxq_info_reg_mem_model(&rx_ring->xdp_rxq,
> + MEM_TYPE_PAGE_SHARED, NULL);
> + if (err) {
> + xdp_rxq_info_unreg(&rx_ring->xdp_rxq);
> + goto err;
> + }
> +
> rx_ring->xdp_prog = adapter->xdp_prog;
>
> return 0;
> diff --git a/drivers/net/tun.c b/drivers/net/tun.c
> index 6750980d9f30..81fddf9cc58f 100644
> --- a/drivers/net/tun.c
> +++ b/drivers/net/tun.c
> @@ -846,6 +846,12 @@ static int tun_attach(struct tun_struct *tun, struct file *file,
> tun->dev, tfile->queue_index);
> if (err < 0)
> goto out;
> + err = xdp_rxq_info_reg_mem_model(&tfile->xdp_rxq,
> + MEM_TYPE_PAGE_SHARED, NULL);
> + if (err < 0) {
> + xdp_rxq_info_unreg(&tfile->xdp_rxq);
> + goto out;
> + }
> err = 0;
> }
>
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index 6c4220450506..48c86accd3b8 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -1312,6 +1312,13 @@ static int virtnet_open(struct net_device *dev)
> if (err < 0)
> return err;
>
> + err = xdp_rxq_info_reg_mem_model(&vi->rq[i].xdp_rxq,
> + MEM_TYPE_PAGE_SHARED, NULL);
> + if (err < 0) {
> + xdp_rxq_info_unreg(&vi->rq[i].xdp_rxq);
> + return err;
> + }
> +
> virtnet_napi_enable(vi->rq[i].vq, &vi->rq[i].napi);
> virtnet_napi_tx_enable(vi, vi->sq[i].vq, &vi->sq[i].napi);
> }
> diff --git a/include/net/xdp.h b/include/net/xdp.h
> index bc0cb97e20dc..859aa9b737fe 100644
> --- a/include/net/xdp.h
> +++ b/include/net/xdp.h
> @@ -41,7 +41,7 @@ enum mem_type {
>
> struct xdp_mem_info {
> u32 type; /* enum mem_type, but known size type */
> - /* u32 id; will be added later in this patchset */
> + u32 id;
> };
>
> struct xdp_rxq_info {
> @@ -100,18 +100,7 @@ struct xdp_frame *convert_to_xdp_frame(struct xdp_buff *xdp)
> return xdp_frame;
> }
>
> -static inline
> -void xdp_return_frame(void *data, struct xdp_mem_info *mem)
> -{
> - if (mem->type == MEM_TYPE_PAGE_SHARED)
> - page_frag_free(data);
> -
> - if (mem->type == MEM_TYPE_PAGE_ORDER0) {
> - struct page *page = virt_to_page(data); /* Assumes order0 page*/
> -
> - put_page(page);
> - }
> -}
> +void xdp_return_frame(void *data, struct xdp_mem_info *mem);
>
> int xdp_rxq_info_reg(struct xdp_rxq_info *xdp_rxq,
> struct net_device *dev, u32 queue_index);
> diff --git a/net/core/xdp.c b/net/core/xdp.c
> index 9eee0c431126..06a5b39491ad 100644
> --- a/net/core/xdp.c
> +++ b/net/core/xdp.c
> @@ -5,6 +5,9 @@
> */
> #include <linux/types.h>
> #include <linux/mm.h>
> +#include <linux/slab.h>
> +#include <linux/idr.h>
> +#include <linux/rhashtable.h>
>
> #include <net/xdp.h>
>
> @@ -13,6 +16,99 @@
> #define REG_STATE_UNREGISTERED 0x2
> #define REG_STATE_UNUSED 0x3
>
> +DEFINE_IDA(mem_id_pool);
> +static DEFINE_MUTEX(mem_id_lock);
> +#define MEM_ID_MAX 0xFFFE
> +#define MEM_ID_MIN 1
> +static int mem_id_next = MEM_ID_MIN;
> +
> +static bool mem_id_init; /* false */
> +static struct rhashtable *mem_id_ht;
> +
> +struct xdp_mem_allocator {
> + struct xdp_mem_info mem;
> + void *allocator;
> + struct rhash_head node;
> + struct rcu_head rcu;
> +};
> +
> +static u32 xdp_mem_id_hashfn(const void *data, u32 len, u32 seed)
> +{
> + const u32 *k = data;
> + const u32 key = *k;
> +
> + BUILD_BUG_ON(FIELD_SIZEOF(struct xdp_mem_allocator, mem.id)
> + != sizeof(u32));
> +
> + /* Use cyclic increasing ID as direct hash key, see rht_bucket_index */
> + return key << RHT_HASH_RESERVED_SPACE;
> +}
> +
> +static int xdp_mem_id_cmp(struct rhashtable_compare_arg *arg,
> + const void *ptr)
> +{
> + const struct xdp_mem_allocator *xa = ptr;
> + u32 mem_id = *(u32 *)arg->key;
> +
> + return xa->mem.id != mem_id;
> +}
> +
> +static const struct rhashtable_params mem_id_rht_params = {
> + .nelem_hint = 64,
> + .head_offset = offsetof(struct xdp_mem_allocator, node),
> + .key_offset = offsetof(struct xdp_mem_allocator, mem.id),
> + .key_len = FIELD_SIZEOF(struct xdp_mem_allocator, mem.id),
> + .max_size = MEM_ID_MAX,
> + .min_size = 8,
> + .automatic_shrinking = true,
> + .hashfn = xdp_mem_id_hashfn,
> + .obj_cmpfn = xdp_mem_id_cmp,
> +};
> +
> +void __xdp_mem_allocator_rcu_free(struct rcu_head *rcu)
> +{
> + struct xdp_mem_allocator *xa;
> +
> + xa = container_of(rcu, struct xdp_mem_allocator, rcu);
> +
> + /* Allow this ID to be reused */
> + ida_simple_remove(&mem_id_pool, xa->mem.id);
> +
> + /* TODO: Depending on allocator type/pointer free resources */
> +
> + /* Poison memory */
> + xa->mem.id = 0xFFFF;
> + xa->mem.type = 0xF0F0;
> + xa->allocator = (void *)0xDEAD9001;
> +
> + kfree(xa);
> +}
> +
> +void __xdp_rxq_info_unreg_mem_model(struct xdp_rxq_info *xdp_rxq)
> +{
> + struct xdp_mem_allocator *xa;
> + int id = xdp_rxq->mem.id;
> + int err;
> +
> + if (id == 0)
> + return;
> +
> + mutex_lock(&mem_id_lock);
> +
> + xa = rhashtable_lookup(mem_id_ht, &id, mem_id_rht_params);
> + if (!xa) {
> + mutex_unlock(&mem_id_lock);
> + return;
> + }
> +
> + err = rhashtable_remove_fast(mem_id_ht, &xa->node, mem_id_rht_params);
> + WARN_ON(err);
> +
> + call_rcu(&xa->rcu, __xdp_mem_allocator_rcu_free);
> +
> + mutex_unlock(&mem_id_lock);
> +}
> +
> void xdp_rxq_info_unreg(struct xdp_rxq_info *xdp_rxq)
> {
> /* Simplify driver cleanup code paths, allow unreg "unused" */
> @@ -21,8 +117,14 @@ void xdp_rxq_info_unreg(struct xdp_rxq_info *xdp_rxq)
>
> WARN(!(xdp_rxq->reg_state == REG_STATE_REGISTERED), "Driver BUG");
>
> + __xdp_rxq_info_unreg_mem_model(xdp_rxq);
> +
> xdp_rxq->reg_state = REG_STATE_UNREGISTERED;
> xdp_rxq->dev = NULL;
> +
> + /* Reset mem info to defaults */
> + xdp_rxq->mem.id = 0;
> + xdp_rxq->mem.type = 0;
> }
> EXPORT_SYMBOL_GPL(xdp_rxq_info_unreg);
>
> @@ -72,20 +174,138 @@ bool xdp_rxq_info_is_reg(struct xdp_rxq_info *xdp_rxq)
> }
> EXPORT_SYMBOL_GPL(xdp_rxq_info_is_reg);
>
> +int __mem_id_init_hash_table(void)
> +{
> + struct rhashtable *rht;
> + int ret;
> +
> + if (unlikely(mem_id_init))
> + return 0;
> +
> + rht = kzalloc(sizeof(*rht), GFP_KERNEL);
> + if (!rht)
> + return -ENOMEM;
> +
> + ret = rhashtable_init(rht, &mem_id_rht_params);
> + if (ret < 0) {
> + kfree(rht);
> + return ret;
> + }
> + mem_id_ht = rht;
> + smp_mb(); /* mutex lock should provide enough pairing */
> + mem_id_init = true;
> +
> + return 0;
> +}
> +
> +/* Allocate a cyclic ID that maps to allocator pointer.
> + * See: https://www.kernel.org/doc/html/latest/core-api/idr.html
> + *
> + * Caller must lock mem_id_lock.
> + */
> +static int __mem_id_cyclic_get(gfp_t gfp)
> +{
> + int retries = 1;
> + int id;
> +
> +again:
> + id = ida_simple_get(&mem_id_pool, mem_id_next, MEM_ID_MAX, gfp);
> + if (id < 0) {
> + if (id == -ENOSPC) {
> + /* Cyclic allocator, reset next id */
> + if (retries--) {
> + mem_id_next = MEM_ID_MIN;
> + goto again;
> + }
> + }
> + return id; /* errno */
> + }
> + mem_id_next = id + 1;
> +
> + return id;
> +}
> +
> int xdp_rxq_info_reg_mem_model(struct xdp_rxq_info *xdp_rxq,
> enum mem_type type, void *allocator)
> {
> + struct xdp_mem_allocator *xdp_alloc;
> + gfp_t gfp = GFP_KERNEL;
> + int id, errno, ret;
> + void *ptr;
> +
> + if (xdp_rxq->reg_state != REG_STATE_REGISTERED) {
> + WARN(1, "Missing register, driver bug");
> + return -EFAULT;
> + }
> +
> if (type >= MEM_TYPE_MAX)
> return -EINVAL;
>
> xdp_rxq->mem.type = type;
>
> - if (allocator)
> - return -EOPNOTSUPP;
> + if (!allocator)
> + return 0;
> +
> + /* Delay init of rhashtable to save memory if feature isn't used */
> + if (!mem_id_init) {
> + mutex_lock(&mem_id_lock);
> + ret = __mem_id_init_hash_table();
> + mutex_unlock(&mem_id_lock);
> + if (ret < 0) {
> + WARN_ON(1);
> + return ret;
> + }
> + }
> +
> + xdp_alloc = kzalloc(sizeof(*xdp_alloc), gfp);
> + if (!xdp_alloc)
> + return -ENOMEM;
> +
> + mutex_lock(&mem_id_lock);
> + id = __mem_id_cyclic_get(gfp);
> + if (id < 0) {
> + errno = id;
> + goto err;
> + }
> + xdp_rxq->mem.id = id;
> + xdp_alloc->mem = xdp_rxq->mem;
> + xdp_alloc->allocator = allocator;
> +
> + /* Insert allocator into ID lookup table */
> + ptr = rhashtable_insert_slow(mem_id_ht, &id, &xdp_alloc->node);
> + if (IS_ERR(ptr)) {
> + errno = PTR_ERR(ptr);
> + goto err;
> + }
> +
> + mutex_unlock(&mem_id_lock);
>
> - /* TODO: Allocate an ID that maps to allocator pointer
> - * See: https://www.kernel.org/doc/html/latest/core-api/idr.html
> - */
> return 0;
> +err:
> + mutex_unlock(&mem_id_lock);
> + kfree(xdp_alloc);
> + return errno;
> }
> EXPORT_SYMBOL_GPL(xdp_rxq_info_reg_mem_model);
> +
> +void xdp_return_frame(void *data, struct xdp_mem_info *mem)
> +{
> + struct xdp_mem_allocator *xa;
> +
> + rcu_read_lock();
> + if (mem->id)
> + xa = rhashtable_lookup(mem_id_ht, &mem->id, mem_id_rht_params);
> + rcu_read_unlock();
> +
> + if (mem->type == MEM_TYPE_PAGE_SHARED) {
> + page_frag_free(data);
> + return;
> + }
> +
> + if (mem->type == MEM_TYPE_PAGE_ORDER0) {
> + struct page *page = virt_to_page(data); /* Assumes order0 page*/
> +
> + put_page(page);
> + }
> +}
> +EXPORT_SYMBOL_GPL(xdp_return_frame);
>

I'm not sure what the point is of getting the xa value if it is not
going to be used. Also I would assume there are types that won't even
need the hash table lookup. I would prefer to see this bit held off on
until you have something that actually needs it.