net: allow skb->head to be a page fragment

skb->head is currently allocated from kmalloc(). This is convenient but
has the drawback the data cannot be converted to a page fragment if
needed.

We have three spots were it hurts :

1) GRO aggregation

 When a linear skb must be appended to another skb, GRO uses the
frag_list fallback, very inefficient since we keep all struct sk_buff
around. So drivers enabling GRO but delivering linear skbs to network
stack aren't enabling full GRO power.

2) splice(socket -> pipe).

 We must copy the linear part to a page fragment.
 This kind of defeats splice() purpose (zero copy claim)

3) TCP coalescing.

 Recently introduced, this permits to group several contiguous segments
into a single skb. This shortens queue lengths and save kernel memory,
and greatly reduce probabilities of TCP collapses. This coalescing
doesnt work on linear skbs (or we would need to copy data, this would be
too slow)

Given all these issues, the following patch introduces the possibility
of having skb->head be a fragment in itself. We use a new skb flag,
skb->head_frag to carry this information.

build_skb() is changed to accept a frag_size argument. Drivers willing
to provide a page fragment instead of kmalloc() data will set a non zero
value, set to the fragment size.

Then, on situations we need to convert the skb head to a frag in itself,
we can check if skb->head_frag is set and avoid the copies or various
fallbacks we have.

This means drivers currently using frags could be updated to avoid the
current skb->head allocation and reduce their memory footprint (aka skb
truesize). (thats 512 or 1024 bytes saved per skb). This also makes
bpf/netfilter faster since the 'first frag' will be part of skb linear
part, no need to copy data.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Ilpo Järvinen <ilpo.jarvinen@helsinki.fi>
Cc: Herbert Xu <herbert@gondor.apana.org.au>
Cc: Maciej Żenczykowski <maze@google.com>
Cc: Neal Cardwell <ncardwell@google.com>
Cc: Tom Herbert <therbert@google.com>
Cc: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Cc: Ben Hutchings <bhutchings@solarflare.com>
Cc: Matt Carlson <mcarlson@broadcom.com>
Cc: Michael Chan <mchan@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/drivers/net/ethernet/broadcom/bnx2.c b/drivers/net/ethernet/broadcom/bnx2.c
index ab55979b37564b779ebefd60ff30ec664566b693..ac7b74488531be6f59ee885c23386b01eabd60f5 100644 (file)
--- a/drivers/net/ethernet/broadcom/bnx2.c
+++ b/drivers/net/ethernet/broadcom/bnx2.c
@@ -3006,7 +3006,7 @@ error:
 
        dma_unmap_single(&bp->pdev->dev, dma_addr, bp->rx_buf_use_size,
                         PCI_DMA_FROMDEVICE);
-       skb = build_skb(data);
+       skb = build_skb(data, 0);
        if (!skb) {
                kfree(data);
                goto error;

diff --git a/drivers/net/ethernet/broadcom/bnx2x/bnx2x_cmn.c b/drivers/net/ethernet/broadcom/bnx2x/bnx2x_cmn.c
index afa6cbb6b193faa091b44c433ba2519d408eeb0c..be0e90382d9eeadc8fd5b8d7ebc5da81869c6380 100644 (file)
--- a/drivers/net/ethernet/broadcom/bnx2x/bnx2x_cmn.c
+++ b/drivers/net/ethernet/broadcom/bnx2x/bnx2x_cmn.c
@@ -513,7 +513,7 @@ static inline void bnx2x_tpa_stop(struct bnx2x *bp, struct bnx2x_fastpath *fp,
        dma_unmap_single(&bp->pdev->dev, dma_unmap_addr(rx_buf, mapping),
                         fp->rx_buf_size, DMA_FROM_DEVICE);
        if (likely(new_data))
-               skb = build_skb(data);
+               skb = build_skb(data, 0);
 
        if (likely(skb)) {
 #ifdef BNX2X_STOP_ON_ERROR
@@ -721,7 +721,7 @@ int bnx2x_rx_int(struct bnx2x_fastpath *fp, int budget)
                                                 dma_unmap_addr(rx_buf, mapping),
                                                 fp->rx_buf_size,
                                                 DMA_FROM_DEVICE);
-                               skb = build_skb(data);
+                               skb = build_skb(data, 0);
                                if (unlikely(!skb)) {
                                        kfree(data);
                                        fp->eth_q_stats.rx_skb_alloc_failed++;

diff --git a/drivers/net/ethernet/broadcom/tg3.c b/drivers/net/ethernet/broadcom/tg3.c
index 0c3e7c70ffbc72d614774553c35a61df084e9045..d481b0a998478e5f0a16711af8b9ba0a7dd9ba95 100644 (file)
--- a/drivers/net/ethernet/broadcom/tg3.c
+++ b/drivers/net/ethernet/broadcom/tg3.c
@@ -5844,7 +5844,7 @@ static int tg3_rx(struct tg3_napi *tnapi, int budget)
                        pci_unmap_single(tp->pdev, dma_addr, skb_size,
                                         PCI_DMA_FROMDEVICE);
 
-                       skb = build_skb(data);
+                       skb = build_skb(data, 0);
                        if (!skb) {
                                kfree(data);
                                goto drop_it_no_recycle;

diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index 4a656b51825ef485bcfaa09b01a8c6130860deea..9d28a22a8554b3e62932e72affc16ae9130599fe 100644 (file)
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -470,7 +470,8 @@ struct sk_buff {
        __u8                    wifi_acked_valid:1;
        __u8                    wifi_acked:1;
        __u8                    no_fcs:1;
-       /* 9/11 bit hole (depending on ndisc_nodetype presence) */
+       __u8                    head_frag:1;
+       /* 8/10 bit hole (depending on ndisc_nodetype presence) */
        kmemcheck_bitfield_end(flags2);
 
 #ifdef CONFIG_NET_DMA
@@ -562,7 +563,7 @@ extern void consume_skb(struct sk_buff *skb);
 extern void           __kfree_skb(struct sk_buff *skb);
 extern struct sk_buff *__alloc_skb(unsigned int size,
                                   gfp_t priority, int fclone, int node);
-extern struct sk_buff *build_skb(void *data);
+extern struct sk_buff *build_skb(void *data, unsigned int frag_size);
 static inline struct sk_buff *alloc_skb(unsigned int size,
                                        gfp_t priority)
 {

diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index 2342a725039114328f1fd3aa129bf1a044e1a52c..effa75d0e318aa2c477d8e3c25da38d80c6299b5 100644 (file)
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -245,6 +245,7 @@ EXPORT_SYMBOL(__alloc_skb);
 /**
  * build_skb - build a network buffer
  * @data: data buffer provided by caller
+ * @frag_size: size of fragment, or 0 if head was kmalloced
  *
  * Allocate a new &sk_buff. Caller provides space holding head and
  * skb_shared_info. @data must have been allocated by kmalloc()
@@ -258,20 +259,21 @@ EXPORT_SYMBOL(__alloc_skb);
  *  before giving packet to stack.
  *  RX rings only contains data buffers, not full skbs.
  */
-struct sk_buff *build_skb(void *data)
+struct sk_buff *build_skb(void *data, unsigned int frag_size)
 {
        struct skb_shared_info *shinfo;
        struct sk_buff *skb;
-       unsigned int size;
+       unsigned int size = frag_size ? : ksize(data);
 
        skb = kmem_cache_alloc(skbuff_head_cache, GFP_ATOMIC);
        if (!skb)
                return NULL;
 
-       size = ksize(data) - SKB_DATA_ALIGN(sizeof(struct skb_shared_info));
+       size -= SKB_DATA_ALIGN(sizeof(struct skb_shared_info));
 
        memset(skb, 0, offsetof(struct sk_buff, tail));
        skb->truesize = SKB_TRUESIZE(size);
+       skb->head_frag = frag_size != 0;
        atomic_set(&skb->users, 1);
        skb->head = data;
        skb->data = data;
@@ -376,6 +378,14 @@ static void skb_clone_fraglist(struct sk_buff *skb)
                skb_get(list);
 }
 
+static void skb_free_head(struct sk_buff *skb)
+{
+       if (skb->head_frag)
+               put_page(virt_to_head_page(skb->head));
+       else
+               kfree(skb->head);
+}
+
 static void skb_release_data(struct sk_buff *skb)
 {
        if (!skb->cloned ||
@@ -402,7 +412,7 @@ static void skb_release_data(struct sk_buff *skb)
                if (skb_has_frag_list(skb))
                        skb_drop_fraglist(skb);
 
-               kfree(skb->head);
+               skb_free_head(skb);
        }
 }
 
@@ -644,6 +654,7 @@ static struct sk_buff *__skb_clone(struct sk_buff *n, struct sk_buff *skb)
        C(tail);
        C(end);
        C(head);
+       C(head_frag);
        C(data);
        C(truesize);
        atomic_set(&n->users, 1);
@@ -940,7 +951,7 @@ int pskb_expand_head(struct sk_buff *skb, int nhead, int ntail,
                fastpath = atomic_read(&skb_shinfo(skb)->dataref) == delta;
        }
 
-       if (fastpath &&
+       if (fastpath && !skb->head_frag &&
            size + sizeof(struct skb_shared_info) <= ksize(skb->head)) {
                memmove(skb->head + size, skb_shinfo(skb),
                        offsetof(struct skb_shared_info,
@@ -967,7 +978,7 @@ int pskb_expand_head(struct sk_buff *skb, int nhead, int ntail,
               offsetof(struct skb_shared_info, frags[skb_shinfo(skb)->nr_frags]));
 
        if (fastpath) {
-               kfree(skb->head);
+               skb_free_head(skb);
        } else {
                /* copy this zero copy skb frags */
                if (skb_shinfo(skb)->tx_flags & SKBTX_DEV_ZEROCOPY) {
@@ -985,6 +996,7 @@ int pskb_expand_head(struct sk_buff *skb, int nhead, int ntail,
        off = (data + nhead) - skb->head;
 
        skb->head     = data;
+       skb->head_frag = 0;
 adjust_others:
        skb->data    += off;
 #ifdef NET_SKBUFF_DATA_USES_OFFSET