From: Arjun Roy arjunroy@google.com
[ Upstream commit 7fba5309efe24e4f0284ef4b8663cdf401035e72 ]
Refactor skb frag fast-forwarding for tcp receive zerocopy. This is part of a patch set that introduces short-circuited hybrid copies for small receive operations, which results in roughly 33% fewer syscalls for small RPC scenarios.
skb_advance_to_frag(), given a skb and an offset into the skb, iterates from the first frag for the skb until we're at the frag specified by the offset. Assuming the offset provided refers to how many bytes in the skb are already read, the returned frag points to the next frag we may read from, while offset_frag is set to the number of bytes from this frag that we have already read.
If frag is not null and offset_frag is equal to 0, then we may be able to map this frag's page into the process address space with vm_insert_page(). However, if offset_frag is not equal to 0, then we cannot do so.
Signed-off-by: Arjun Roy arjunroy@google.com Signed-off-by: Eric Dumazet edumazet@google.com Signed-off-by: Soheil Hassas Yeganeh soheil@google.com Signed-off-by: Jakub Kicinski kuba@kernel.org Signed-off-by: Sasha Levin sashal@kernel.org --- net/ipv4/tcp.c | 35 ++++++++++++++++++++++++++--------- 1 file changed, 26 insertions(+), 9 deletions(-)
diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c index ba6e4c6db3b0a..b3721cff45023 100644 --- a/net/ipv4/tcp.c +++ b/net/ipv4/tcp.c @@ -1746,6 +1746,28 @@ int tcp_mmap(struct file *file, struct socket *sock, } EXPORT_SYMBOL(tcp_mmap);
+static skb_frag_t *skb_advance_to_frag(struct sk_buff *skb, u32 offset_skb, + u32 *offset_frag) +{ + skb_frag_t *frag; + + offset_skb -= skb_headlen(skb); + if ((int)offset_skb < 0 || skb_has_frag_list(skb)) + return NULL; + + frag = skb_shinfo(skb)->frags; + while (offset_skb) { + if (skb_frag_size(frag) > offset_skb) { + *offset_frag = offset_skb; + return frag; + } + offset_skb -= skb_frag_size(frag); + ++frag; + } + *offset_frag = 0; + return frag; +} + static int tcp_copy_straggler_data(struct tcp_zerocopy_receive *zc, struct sk_buff *skb, u32 copylen, u32 *offset, u32 *seq) @@ -1872,6 +1894,8 @@ static int tcp_zerocopy_receive(struct sock *sk, curr_addr = address; while (length + PAGE_SIZE <= zc->length) { if (zc->recv_skip_hint < PAGE_SIZE) { + u32 offset_frag; + /* If we're here, finish the current batch. */ if (pg_idx) { ret = tcp_zerocopy_vm_insert_batch(vma, pages, @@ -1892,16 +1916,9 @@ static int tcp_zerocopy_receive(struct sock *sk, skb = tcp_recv_skb(sk, seq, &offset); } zc->recv_skip_hint = skb->len - offset; - offset -= skb_headlen(skb); - if ((int)offset < 0 || skb_has_frag_list(skb)) + frags = skb_advance_to_frag(skb, offset, &offset_frag); + if (!frags || offset_frag) break; - frags = skb_shinfo(skb)->frags; - while (offset) { - if (skb_frag_size(frags) > offset) - goto out; - offset -= skb_frag_size(frags); - frags++; - } } if (skb_frag_size(frags) != PAGE_SIZE || skb_frag_off(frags)) { int remaining = zc->recv_skip_hint;