[PATCH 2/2] tcp: cleanup tcp_try_coalesce

Alexander Duyck
2012-05-03T03:38:47Z

This change is mostly meant to help improve the readability of
tcp_try_coalesce. I had a few issues since there were several points when
the code would test for a conditional, fail, then succeed on another
conditional take some action, and then follow a goto back into the previous
conditional. I just tore all of that apart and made the whole thing one
linear flow with a single goto.

Also there were multiple ways of computing the delta, the one for head_frag
made the least amount of sense to me since we were only dropping the
sk_buff so I have updated the logic for the stolen head case so that delta
is only truesize - sizeof(skb_buff), and for the case where we are dropping
the head as well it is truesize - SKB_TRUESIZE(skb_end_pointer - head).
This way we can also account for the head_frag with headlen == 0.

Signed-off-by: Alexander Duyck <alexander.h.duyck@intel.com>
Cc: Eric Dumazet <edumazet@google.com>
Cc: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
---

net/ipv4/tcp_input.c | 80 +++++++++++++++++++++++++++-----------------------
1 files changed, 43 insertions(+), 37 deletions(-)

diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index c6f78e2..23bc3ff 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -4548,62 +4548,68 @@ static bool tcp_try_coalesce(struct sock *sk,
int i, delta, len = from->len;

*fragstolen = false;
+
if (tcp_hdr(from)->fin || skb_cloned(to))
return false;
+
if (len <= skb_tailroom(to)) {
BUG_ON(skb_copy_bits(from, 0, skb_put(to, len), len));
-merge:
- NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPRCVCOALESCE);
- TCP_SKB_CB(to)->end_seq = TCP_SKB_CB(from)->end_seq;
- TCP_SKB_CB(to)->ack_seq = TCP_SKB_CB(from)->ack_seq;
- return true;
+ goto merge;
}

if (skb_has_frag_list(to) || skb_has_frag_list(from))
return false;

- if (skb_headlen(from) == 0 &&
- (skb_shinfo(to)->nr_frags +
- skb_shinfo(from)->nr_frags <= MAX_SKB_FRAGS)) {
- WARN_ON_ONCE(from->head_frag);
- delta = from->truesize - ksize(from->head) -
- SKB_DATA_ALIGN(sizeof(struct sk_buff));
-
- WARN_ON_ONCE(delta < len);
-copyfrags:
- memcpy(skb_shinfo(to)->frags + skb_shinfo(to)->nr_frags,
- skb_shinfo(from)->frags,
- skb_shinfo(from)->nr_frags * sizeof(skb_frag_t));
- skb_shinfo(to)->nr_frags += skb_shinfo(from)->nr_frags;
-
- if (skb_cloned(from))
- for (i = 0; i < skb_shinfo(from)->nr_frags; i++)
- skb_frag_ref(from, i);
- else
- skb_shinfo(from)->nr_frags = 0;
-
- to->truesize += delta;
- atomic_add(delta, &sk->sk_rmem_alloc);
- sk_mem_charge(sk, delta);
- to->len += len;
- to->data_len += len;
- goto merge;
- }
- if (from->head_frag && !skb_cloned(from)) {
+ if (skb_headlen(from) != 0) {
struct page *page;
unsigned int offset;

- if (skb_shinfo(to)->nr_frags + skb_shinfo(from)->nr_frags >= MAX_SKB_FRAGS)
+ if (skb_shinfo(to)->nr_frags +
+ skb_shinfo(from)->nr_frags >= MAX_SKB_FRAGS)
+ return false;
+
+ if (!from->head_frag || skb_cloned(from))
return false;
+
+ delta = from->truesize - sizeof(struct sk_buff);
+
page = virt_to_head_page(from->head);
offset = from->data - (unsigned char *)page_address(page);
+
skb_fill_page_desc(to, skb_shinfo(to)->nr_frags,
page, offset, skb_headlen(from));
*fragstolen = true;
- delta = len; /* we dont know real truesize... */
- goto copyfrags;
+ } else {
+ if (skb_shinfo(to)->nr_frags +
+ skb_shinfo(from)->nr_frags > MAX_SKB_FRAGS)
+ return false;
+
+ delta = from->truesize -
+ SKB_TRUESIZE(skb_end_pointer(from) - from->head);
}
- return false;
+
+ memcpy(skb_shinfo(to)->frags + skb_shinfo(to)->nr_frags,
+ skb_shinfo(from)->frags,
+ skb_shinfo(from)->nr_frags * sizeof(skb_frag_t));
+ skb_shinfo(to)->nr_frags += skb_shinfo(from)->nr_frags;
+
+ if (!skb_cloned(from))
+ skb_shinfo(from)->nr_frags = 0;
+
+ for (i = 0; i < skb_shinfo(from)->nr_frags; i++)
+ skb_frag_ref(from, i);
+
+ to->truesize += delta;
+ atomic_add(delta, &sk->sk_rmem_alloc);
+ sk_mem_charge(sk, delta);
+ to->len += len;
+ to->data_len += len;
+
+merge:
+ NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPRCVCOALESCE);
+ TCP_SKB_CB(to)->end_seq = TCP_SKB_CB(from)->end_seq;
+ TCP_SKB_CB(to)->ack_seq = TCP_SKB_CB(from)->ack_seq;
+ return true;
}

static void kfree_skb_partial(struct sk_buff *skb, bool head_stolen)