From a21d45726acacc963d8baddf74607d9b74e2b723 Mon Sep 17 00:00:00 2001 From: Eric Dumazet Date: Tue, 10 Apr 2012 20:30:48 +0000 Subject: 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 Tested-by: Marc MERLIN Signed-off-by: Eric Dumazet Signed-off-by: David S. Miller --- include/linux/skbuff.h | 13 +++++++++++++ 1 file changed, 13 insertions(+) (limited to 'include/linux/skbuff.h') diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h index 33370271b8b..70a3f8d4911 100644 --- a/include/linux/skbuff.h +++ b/include/linux/skbuff.h @@ -481,6 +481,7 @@ struct sk_buff { union { __u32 mark; __u32 dropcount; + __u32 avail_size; }; sk_buff_data_t transport_header; @@ -1365,6 +1366,18 @@ static inline int skb_tailroom(const struct sk_buff *skb) return skb_is_nonlinear(skb) ? 0 : skb->end - skb->tail; } +/** + * skb_availroom - bytes at buffer end + * @skb: buffer to check + * + * Return the number of bytes of free space at the tail of an sk_buff + * allocated by sk_stream_alloc() + */ +static inline int skb_availroom(const struct sk_buff *skb) +{ + return skb_is_nonlinear(skb) ? 0 : skb->avail_size - skb->len; +} + /** * skb_reserve - adjust headroom * @skb: buffer to alter -- cgit v1.2.3-70-g09d2