[RFC PATCH v7 08/19] Make __alloc_skb() to get external buffer.

xiaohui.xin
2010-06-05T10:14:47Z

From: Xin Xiaohui <xiaohui.xin@intel.com>

Add a dev parameter to __alloc_skb(), skb->data
points to external buffer, recompute skb->head,
maintain shinfo of the external buffer, record
external buffer info into destructor_arg field.

Signed-off-by: Xin Xiaohui <xiaohui.xin@intel.com>
Signed-off-by: Zhao Yu <yzhao81new@gmail.com>
Reviewed-by: Jeff Dike <jdike@linux.intel.com>
---

__alloc_skb() cleanup by

Jeff Dike <jdike@linux.intel.com>

include/linux/skbuff.h | 7 ++++---
net/core/skbuff.c | 43 +++++++++++++++++++++++++++++++++++++------
2 files changed, 41 insertions(+), 9 deletions(-)

diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index 281a1c0..5ff8c27 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -442,17 +442,18 @@ extern void kfree_skb(struct sk_buff *skb);
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);
+ gfp_t priority, int fclone,
+ int node, struct net_device *dev);
static inline struct sk_buff *alloc_skb(unsigned int size,
gfp_t priority)
{
- return __alloc_skb(size, priority, 0, -1);
+ return __alloc_skb(size, priority, 0, -1, NULL);
}

static inline struct sk_buff *alloc_skb_fclone(unsigned int size,
gfp_t priority)
{
- return __alloc_skb(size, priority, 1, -1);
+ return __alloc_skb(size, priority, 1, -1, NULL);
}

extern int skb_recycle_check(struct sk_buff *skb, int skb_size);
diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index fbdb1f1..38d19d0 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -161,7 +161,8 @@ EXPORT_SYMBOL(skb_under_panic);
* @fclone: allocate from fclone cache instead of head cache
* and allocate a cloned (child) skb
* @node: numa node to allocate memory on
- *
+ * @dev: a device owns the skb if the skb try to get external buffer.
+ * otherwise is NULL.
* Allocate a new &sk_buff. The returned buffer has no headroom and a
* tail room of size bytes. The object has a reference count of one.
* The return is the buffer. On a failure the return is %NULL.
@@ -170,12 +171,13 @@ EXPORT_SYMBOL(skb_under_panic);
* %GFP_ATOMIC.
*/
struct sk_buff *__alloc_skb(unsigned int size, gfp_t gfp_mask,
- int fclone, int node)
+ int fclone, int node, struct net_device *dev)
{
struct kmem_cache *cache;
struct skb_shared_info *shinfo;
struct sk_buff *skb;
- u8 *data;
+ u8 *data = NULL;
+ struct skb_external_page *ext_page = NULL;

cache = fclone ? skbuff_fclone_cache : skbuff_head_cache;

@@ -185,8 +187,23 @@ struct sk_buff *__alloc_skb(unsigned int size, gfp_t gfp_mask,
goto out;

size = SKB_DATA_ALIGN(size);
- data = kmalloc_node_track_caller(size + sizeof(struct skb_shared_info),
- gfp_mask, node);
+
+ /* If the device wants to do mediate passthru(zero-copy),
+ * the skb may try to get external buffers from outside.
+ * If fails, then fall back to alloc buffers from kernel.
+ */
+ if (dev && dev->mp_port) {
+ ext_page = netdev_alloc_external_page(dev, skb, size);
+ if (ext_page) {
+ data = ext_page->start;
+ size = ext_page->size;
+ }
+ }
+
+ if (!data)
+ data = kmalloc_node_track_caller(
+ size + sizeof(struct skb_shared_info),
+ gfp_mask, node);
if (!data)
goto nodata;

@@ -208,6 +225,15 @@ struct sk_buff *__alloc_skb(unsigned int size, gfp_t gfp_mask,
skb->mac_header = ~0U;
#endif

+ /* If the skb get external buffers sucessfully, since the shinfo is
+ * at the end of the buffer, we may retain the shinfo once we
+ * need it sometime.
+ */
+ if (ext_page) {
+ skb->head = skb->data - NET_IP_ALIGN - NET_SKB_PAD;
+ memcpy(ext_page->ushinfo, skb_shinfo(skb),
+ sizeof(struct skb_shared_info));
+ }
/* make sure we initialize shinfo sequentially */
shinfo = skb_shinfo(skb);
atomic_set(&shinfo->dataref, 1);
@@ -231,6 +257,11 @@ struct sk_buff *__alloc_skb(unsigned int size, gfp_t gfp_mask,

child->fclone = SKB_FCLONE_UNAVAILABLE;
}
+ /* Record the external buffer info in this field. It's not so good,
+ * but we cannot find another place easily.
+ */
+ shinfo->destructor_arg = ext_page;
+
out:
return skb;
nodata:
@@ -259,7 +290,7 @@ struct sk_buff *__netdev_alloc_skb(struct net_device *dev,
int node = dev->dev.parent ? dev_to_node(dev->dev.parent) : -1;
struct sk_buff *skb;

- skb = __alloc_skb(length + NET_SKB_PAD, gfp_mask, 0, node);
+ skb = __alloc_skb(length + NET_SKB_PAD, gfp_mask, 0, node, dev);
if (likely(skb)) {
skb_reserve(skb, NET_SKB_PAD);
skb->dev = dev;
--
1.5.4.4