From: Eric Dumazet <eric.dumazet@xxxxxxxxx> Date: Wed, 11 Apr 2012 08:30:48 +0200 > 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@xxxxxxxxxxx> > Tested-by: Marc MERLIN <marc@xxxxxxxxxxx> > Signed-off-by: Eric Dumazet <eric.dumazet@xxxxxxxxx> Applied and queued up for -stable, thanks Eric. -- To unsubscribe from this list: send the line "unsubscribe linux-wireless" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
