[PATCH net-next resubmit] skbuff: optimize the pull_pages code in __pskb_pull_tail()

In the pull_pages code block, if the first frag size > eat,
we can end the loop in advance to avoid extra copy.

Signed-off-by: Lin Zhang <redacted>
---
 net/core/skbuff.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index f990eb8..c00a1df 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c

@@ -1720,6 +1720,10 @@ void *__pskb_pull_tail(struct sk_buff *skb, int delta)
 				skb_shinfo(skb)->frags[k].page_offset += eat;
 				skb_frag_size_sub(&skb_shinfo(skb)->frags[k], eat);
 				eat = 0;
+				if (!i) {
+					k = skb_shinfo(skb)->nr_frags;
+					break;
+				}
 			}
 			k++;
 		}

On Mon, 2017-07-17 at 10:22 +0800, Lin Zhang wrote:

quoted

In the pull_pages code block, if the first frag size > eat,
we can end the loop in advance to avoid extra copy.

Signed-off-by: Lin Zhang <redacted>
---
 net/core/skbuff.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index f990eb8..c00a1df 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c

@@ -1720,6 +1720,10 @@ void *__pskb_pull_tail(struct sk_buff *skb, int delta)
                              skb_shinfo(skb)->frags[k].page_offset += eat;
                              skb_frag_size_sub(&skb_shinfo(skb)->frags[k], eat);
                              eat = 0;
+                             if (!i) {
+                                     k = skb_shinfo(skb)->nr_frags;
+                                     break;
+                             }
                      }
                      k++;
              }

-CC lkml  (no need to spam lkml for netdev patches )

Why even reading skb_shinfo(skb)->nr_frags to write it again ?

I would use something like :

diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index 8b11341ed69ad97d34dd3e9b73c8c44ef7c452ff..a562b0e61afa3faf7abdd7f9209ae9096310fb7d 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c

@@ -1719,13 +1719,15 @@ void *__pskb_pull_tail(struct sk_buff *skb, int delta)
                        if (eat) {
                                skb_shinfo(skb)->frags[k].page_offset += eat;
                                skb_frag_size_sub(&skb_shinfo(skb)->frags[k], eat);
+                               if (!i)
+                                       goto end;
                                eat = 0;
                        }
                        k++;
                }
        }
        skb_shinfo(skb)->nr_frags = k;
-
+end:
        skb->tail     += delta;
        skb->data_len -= delta;