netdev - [PATCH net-next 0/2] net: use kmem_cache_free_bulk in kfree_skb

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Date:   Thu, 05 Jan 2023 16:42:37 +0100
From:   Jesper Dangaard Brouer <brouer@...hat.com>
To:     netdev@...r.kernel.org
Cc:     Jesper Dangaard Brouer <brouer@...hat.com>,
        Jakub Kicinski <kuba@...nel.org>,
        "David S. Miller" <davem@...emloft.net>, edumazet@...gle.com,
        pabeni@...hat.com
Subject: [PATCH net-next 0/2] net: use kmem_cache_free_bulk in kfree_skb_list

The kfree_skb_list function walks SKB (via skb->next) and frees them
individually to the SLUB/SLAB allocator (kmem_cache). It is more
efficient to bulk free them via the kmem_cache_free_bulk API.

Netstack NAPI fastpath already uses kmem_cache bulk alloc and free
APIs for SKBs.

The kfree_skb_list call got an interesting optimization in commit
520ac30f4551 ("net_sched: drop packets after root qdisc lock is
released") that can create a list of SKBs "to_free" e.g. when qdisc
enqueue fails or deliberately chooses to drop . It isn't a normal data
fastpath, but the situation will likely occur when system/qdisc are
under heavy workloads, thus it makes sense to use a faster API for
freeing the SKBs.

E.g. the (often distro default) qdisc fq_codel will drop batches of
packets from fattest elephant flow, default capped at 64 packets (but
adjustable via tc argument drop_batch).

---

Jesper Dangaard Brouer (2):
      net: fix call location in kfree_skb_list_reason
      net: kfree_skb_list use kmem_cache_free_bulk

 net/core/skbuff.c | 67 +++++++++++++++++++++++++++++++++++++++--------
 1 file changed, 56 insertions(+), 11 deletions(-)

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