Re: [PATCH] tcp: splice as many packets as possible at once

David Miller
2009-01-14T00:37:23Z

From: Evgeniy Polyakov <zbr@ioremap.net>
Date: Wed, 14 Jan 2009 03:22:52 +0300

> On Tue, Jan 13, 2009 at 04:16:25PM -0800, David Miller (davem@davemloft.net) wrote:
> > I wish there were some way we could make this code grab and release a
> > reference to the SKB data area (I mean skb_shinfo(skb)->dataref) to
> > accomplish it's goals.
>
> Ugh... Clone without cloninig, but by increasing the dataref. Getting
> that splice only needs that skb to track the head of the original, this
> may really work.

Here is something I scrambled together, it is largely based upon
Jarek's patch:

diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index 5110b35..05126da 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -70,12 +70,17 @@
static struct kmem_cache *skbuff_head_cache __read_mostly;
static struct kmem_cache *skbuff_fclone_cache __read_mostly;

+static void skb_release_data(struct sk_buff *skb);
+
static void sock_pipe_buf_release(struct pipe_inode_info *pipe,
struct pipe_buffer *buf)
{
struct sk_buff *skb = (struct sk_buff *) buf->private;

- kfree_skb(skb);
+ if (skb)
+ skb_release_data(skb);
+ else
+ put_page(buf->page);
}

static void sock_pipe_buf_get(struct pipe_inode_info *pipe,
@@ -83,7 +88,10 @@ static void sock_pipe_buf_get(struct pipe_inode_info *pipe,
{
struct sk_buff *skb = (struct sk_buff *) buf->private;

- skb_get(skb);
+ if (skb)
+ atomic_inc(&skb_shinfo(skb)->dataref);
+ else
+ get_page(buf->page);
}

static int sock_pipe_buf_steal(struct pipe_inode_info *pipe,
@@ -1336,7 +1344,10 @@ static void sock_spd_release(struct splice_pipe_desc *spd, unsigned int i)
{
struct sk_buff *skb = (struct sk_buff *) spd->partial[i].private;

- kfree_skb(skb);
+ if (skb)
+ skb_release_data(skb);
+ else
+ put_page(spd->pages[i]);
}

/*
@@ -1344,7 +1355,7 @@ static void sock_spd_release(struct splice_pipe_desc *spd, unsigned int i)
*/
static inline int spd_fill_page(struct splice_pipe_desc *spd, struct page *page,
unsigned int len, unsigned int offset,
- struct sk_buff *skb)
+ struct sk_buff *skb, int linear)
{
if (unlikely(spd->nr_pages == PIPE_BUFFERS))
return 1;
@@ -1352,8 +1363,15 @@ static inline int spd_fill_page(struct splice_pipe_desc *spd, struct page *page,
spd->pages[spd->nr_pages] = page;
spd->partial[spd->nr_pages].len = len;
spd->partial[spd->nr_pages].offset = offset;
- spd->partial[spd->nr_pages].private = (unsigned long) skb_get(skb);
+ spd->partial[spd->nr_pages].private =
+ (unsigned long) (linear ? skb : NULL);
spd->nr_pages++;
+
+ if (linear)
+ atomic_inc(&skb_shinfo(skb)->dataref);
+ else
+ get_page(page);
+
return 0;
}

@@ -1369,7 +1387,7 @@ static inline void __segment_seek(struct page **page, unsigned int *poff,
static inline int __splice_segment(struct page *page, unsigned int poff,
unsigned int plen, unsigned int *off,
unsigned int *len, struct sk_buff *skb,
- struct splice_pipe_desc *spd)
+ struct splice_pipe_desc *spd, int linear)
{
if (!*len)
return 1;
@@ -1392,7 +1410,7 @@ static inline int __splice_segment(struct page *page, unsigned int poff,
/* the linear region may spread across several pages */
flen = min_t(unsigned int, flen, PAGE_SIZE - poff);

- if (spd_fill_page(spd, page, flen, poff, skb))
+ if (spd_fill_page(spd, page, flen, poff, skb, linear))
return 1;

__segment_seek(&page, &poff, &plen, flen);
@@ -1419,7 +1437,7 @@ static int __skb_splice_bits(struct sk_buff *skb, unsigned int *offset,
if (__splice_segment(virt_to_page(skb->data),
(unsigned long) skb->data & (PAGE_SIZE - 1),
skb_headlen(skb),
- offset, len, skb, spd))
+ offset, len, skb, spd, 1))
return 1;

/*
@@ -1429,7 +1447,7 @@ static int __skb_splice_bits(struct sk_buff *skb, unsigned int *offset,
const skb_frag_t *f = &skb_shinfo(skb)->frags[seg];

if (__splice_segment(f->page, f->page_offset, f->size,
- offset, len, skb, spd))
+ offset, len, skb, spd, 0))
return 1;
}