a21d45726a
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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