Messages in this thread Patch in this message | | | Date | Wed, 09 May 2012 06:51:44 +0100 | From | Ben Hutchings <> | Subject | [ 075/167] [PATCH 15/26] tcp: avoid order-1 allocations on wifi and tx path |
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3.2-stable review patch. If anyone has any objections, please let me know.
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From: Eric Dumazet <eric.dumazet@gmail.com>
[ This combines upstream commit a21d45726acacc963d8baddf74607d9b74e2b723 and the follow-on bug fix commit 22b4a4f22da4b39c6f7f679fd35f3d35c91bf851 ]
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> [bwh: Correct commit hash for follow-on bug fix] Signed-off-by: Ben Hutchings <ben@decadent.org.uk> --- include/linux/skbuff.h | 13 +++++++++++++ net/ipv4/tcp.c | 8 ++++---- net/ipv4/tcp_output.c | 3 ++- 3 files changed, 19 insertions(+), 5 deletions(-)
diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h index 6cf8b53..e689b47 100644 --- a/include/linux/skbuff.h +++ b/include/linux/skbuff.h @@ -458,6 +458,7 @@ struct sk_buff { union { __u32 mark; __u32 dropcount; + __u32 avail_size; }; __u16 vlan_tci; @@ -1326,6 +1327,18 @@ static inline int skb_tailroom(const struct sk_buff *skb) } /** + * 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 * @len: bytes to move diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c index 36611ab..7904db4 100644 --- a/net/ipv4/tcp.c +++ b/net/ipv4/tcp.c @@ -701,11 +701,12 @@ struct sk_buff *sk_stream_alloc_skb(struct sock *sk, int size, gfp_t gfp) skb = alloc_skb_fclone(size + sk->sk_prot->max_header, gfp); if (skb) { if (sk_wmem_schedule(sk, skb->truesize)) { + skb_reserve(skb, sk->sk_prot->max_header); /* * Make sure that we have exactly size bytes * available to the caller, no more, no less. */ - skb_reserve(skb, skb_tailroom(skb) - size); + skb->avail_size = size; return skb; } __kfree_skb(skb); @@ -995,10 +996,9 @@ new_segment: copy = seglen; /* Where to copy to? */ - if (skb_tailroom(skb) > 0) { + if (skb_availroom(skb) > 0) { /* We have some space in skb head. Superb! */ - if (copy > skb_tailroom(skb)) - copy = skb_tailroom(skb); + copy = min_t(int, copy, skb_availroom(skb)); err = skb_add_data_nocache(sk, skb, from, copy); if (err) goto do_fault; diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c index 7413437..c51dd5b 100644 --- a/net/ipv4/tcp_output.c +++ b/net/ipv4/tcp_output.c @@ -1096,6 +1096,7 @@ static void __pskb_trim_head(struct sk_buff *skb, int len) eat = min_t(int, len, skb_headlen(skb)); if (eat) { __skb_pull(skb, eat); + skb->avail_size -= eat; len -= eat; if (!len) return; @@ -2060,7 +2061,7 @@ static void tcp_retrans_try_collapse(struct sock *sk, struct sk_buff *to, /* Punt if not enough space exists in the first SKB for * the data in the second */ - if (skb->len > skb_tailroom(to)) + if (skb->len > skb_availroom(to)) break; if (after(TCP_SKB_CB(skb)->end_seq, tcp_wnd_end(tp))) -- 1.7.10
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