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authorEric Dumazet <eric.dumazet@gmail.com>2012-04-24 23:01:22 -0400
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2012-04-27 10:17:06 -0700
commit0df29c4a2857ed43ff23689423144aaf4f4101bc (patch)
treee60e1c81cd20818bf597201f7c51585592ce13eb
parent1cf9d571c6e48f15608203fc76fa29c617459e0c (diff)
tcp: avoid order-1 allocations on wifi and tx path
[ This combines upstream commit a21d45726acacc963d8baddf74607d9b74e2b723 and the follow-on bug fix commit a21d45726acacc963d8baddf74607d9b74e2b723 ] 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> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
-rw-r--r--include/linux/skbuff.h13
-rw-r--r--net/ipv4/tcp.c8
-rw-r--r--net/ipv4/tcp_output.c3
3 files changed, 19 insertions, 5 deletions
diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index ae86adee3746..42854cee6fc1 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -468,6 +468,7 @@ struct sk_buff {
union {
__u32 mark;
__u32 dropcount;
+ __u32 avail_size;
};
__u16 vlan_tci;
@@ -1338,6 +1339,18 @@ 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 86014bbd3e34..8c8502119161 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -699,11 +699,12 @@ 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);
@@ -993,10 +994,9 @@ 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 4ff3b6dc74fc..e2c6722f7170 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)))