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tcp: avoid order-1 allocations on wifi and tx path
Marc Merlin reported many order-1 allocations failures in TX path on its wireless setup, that dont make any sense with MTU=1500 network, and non SG capable hardware. After investigation, it turns out TCP uses sk_stream_alloc_skb() and used as a convention skb_tailroom(skb) to know how many bytes of data payload could be put in this skb (for non SG capable devices) Note : these skb used kmalloc-4096 (MTU=1500 + MAX_HEADER + sizeof(struct skb_shared_info) being above 2048) Later, mac80211 layer need to add some bytes at the tail of skb (IEEE80211_ENCRYPT_TAILROOM = 18 bytes) and since no more tailroom is available has to call pskb_expand_head() and request order-1 allocations. This patch changes sk_stream_alloc_skb() so that only sk->sk_prot->max_header bytes of headroom are reserved, and use a new skb field, avail_size to hold the data payload limit. This way, order-0 allocations done by TCP stack can leave more than 2 KB of tailroom and no more allocation is performed in mac80211 layer (or any layer needing some tailroom) avail_size is unioned with mark/dropcount, since mark will be set later in IP stack for output packets. Therefore, skb size is unchanged. Reported-by: Marc MERLIN <marc@merlins.org> Tested-by: Marc MERLIN <marc@merlins.org> Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com> Signed-off-by: David S. Miller <davem@davemloft.net>
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parent
87151b8689
commit
a21d45726a
3 changed files with 18 additions and 5 deletions
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@ -481,6 +481,7 @@ struct sk_buff {
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union {
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__u32 mark;
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__u32 dropcount;
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__u32 avail_size;
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};
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sk_buff_data_t transport_header;
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@ -1365,6 +1366,18 @@ static inline int skb_tailroom(const struct sk_buff *skb)
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return skb_is_nonlinear(skb) ? 0 : skb->end - skb->tail;
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}
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/**
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* skb_availroom - bytes at buffer end
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* @skb: buffer to check
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*
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* Return the number of bytes of free space at the tail of an sk_buff
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* allocated by sk_stream_alloc()
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*/
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static inline int skb_availroom(const struct sk_buff *skb)
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{
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return skb_is_nonlinear(skb) ? 0 : skb->avail_size - skb->len;
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}
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/**
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* skb_reserve - adjust headroom
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* @skb: buffer to alter
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@ -701,11 +701,12 @@ struct sk_buff *sk_stream_alloc_skb(struct sock *sk, int size, gfp_t gfp)
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skb = alloc_skb_fclone(size + sk->sk_prot->max_header, gfp);
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if (skb) {
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if (sk_wmem_schedule(sk, skb->truesize)) {
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skb_reserve(skb, sk->sk_prot->max_header);
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/*
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* Make sure that we have exactly size bytes
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* available to the caller, no more, no less.
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*/
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skb_reserve(skb, skb_tailroom(skb) - size);
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skb->avail_size = size;
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return skb;
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}
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__kfree_skb(skb);
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@ -995,10 +996,9 @@ int tcp_sendmsg(struct kiocb *iocb, struct sock *sk, struct msghdr *msg,
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copy = seglen;
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/* Where to copy to? */
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if (skb_tailroom(skb) > 0) {
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if (skb_availroom(skb) > 0) {
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/* We have some space in skb head. Superb! */
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if (copy > skb_tailroom(skb))
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copy = skb_tailroom(skb);
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copy = min_t(int, copy, skb_availroom(skb));
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err = skb_add_data_nocache(sk, skb, from, copy);
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if (err)
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goto do_fault;
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@ -2060,7 +2060,7 @@ static void tcp_retrans_try_collapse(struct sock *sk, struct sk_buff *to,
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/* Punt if not enough space exists in the first SKB for
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* the data in the second
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*/
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if (skb->len > skb_tailroom(to))
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if (skb->len > skb_availroom(to))
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break;
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if (after(TCP_SKB_CB(skb)->end_seq, tcp_wnd_end(tp)))
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