net: speedup skb_splice_bits()

Commit 35f3d14db (pipe: add support for shrinking and growing pipes)
added a slowdown for splice(socket -> pipe), as we might grow the spd
used in skb_splice_bits() for each skb we process in splice() syscall.

Its not needed since skb lengths are capped. The default on-stack arrays
are more than enough.

Use MAX_SKB_FRAGS instead of PIPE_DEF_BUFFERS to describe the reasonable
limit per skb.

Add coalescing support to help splicing of GRO skbs built from linear
skbs (linked into frag_list)

Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Tom Herbert <therbert@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index bf257de95d2682b99abf7f95544f0062405473b3..dfb304066f227fb835e4dabde7c6e4ecf010511a 100644 (file)
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -1581,11 +1581,20 @@ new_page:
        memcpy(page_address(p) + off, page_address(page) + *offset, *len);
        sk->sk_sndmsg_off += *len;
        *offset = off;
-       get_page(p);
 
        return p;
 }
 
+static bool spd_can_coalesce(const struct splice_pipe_desc *spd,
+                            struct page *page,
+                            unsigned int offset)
+{
+       return  spd->nr_pages &&
+               spd->pages[spd->nr_pages - 1] == page &&
+               (spd->partial[spd->nr_pages - 1].offset +
+                spd->partial[spd->nr_pages - 1].len == offset);
+}
+
 /*
  * Fill page/offset/length into spd, if it can hold more pages.
  */
@@ -1595,16 +1604,19 @@ static inline int spd_fill_page(struct splice_pipe_desc *spd,
                                struct sk_buff *skb, int linear,
                                struct sock *sk)
 {
-       if (unlikely(spd->nr_pages == pipe->buffers))
+       if (unlikely(spd->nr_pages == MAX_SKB_FRAGS))
                return 1;
 
        if (linear) {
                page = linear_to_page(page, len, &offset, skb, sk);
                if (!page)
                        return 1;
-       } else
-               get_page(page);
-
+       }
+       if (spd_can_coalesce(spd, page, offset)) {
+               spd->partial[spd->nr_pages - 1].len += *len;
+               return 0;
+       }
+       get_page(page);
        spd->pages[spd->nr_pages] = page;
        spd->partial[spd->nr_pages].len = *len;
        spd->partial[spd->nr_pages].offset = offset;
@@ -1710,8 +1722,8 @@ int skb_splice_bits(struct sk_buff *skb, unsigned int offset,
                    struct pipe_inode_info *pipe, unsigned int tlen,
                    unsigned int flags)
 {
-       struct partial_page partial[PIPE_DEF_BUFFERS];
-       struct page *pages[PIPE_DEF_BUFFERS];
+       struct partial_page partial[MAX_SKB_FRAGS];
+       struct page *pages[MAX_SKB_FRAGS];
        struct splice_pipe_desc spd = {
                .pages = pages,
                .partial = partial,
@@ -1723,9 +1735,6 @@ int skb_splice_bits(struct sk_buff *skb, unsigned int offset,
        struct sock *sk = skb->sk;
        int ret = 0;
 
-       if (splice_grow_spd(pipe, &spd))
-               return -ENOMEM;
-
        /*
         * __skb_splice_bits() only fails if the output has no room left,
         * so no point in going over the frag_list for the error case.
@@ -1761,7 +1770,6 @@ done:
                lock_sock(sk);
        }
 
-       splice_shrink_spd(pipe, &spd);
        return ret;
 }