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Message-ID: <1411738501.16953.122.camel@edumazet-glaptop2.roam.corp.google.com>
Date: Fri, 26 Sep 2014 06:35:01 -0700
From: Eric Dumazet <eric.dumazet@...il.com>
To: David Miller <davem@...emloft.net>
Cc: netdev <netdev@...r.kernel.org>
Subject: Re: [RFC] fclone layout suboptimal
On Fri, 2014-09-26 at 06:07 -0700, Eric Dumazet wrote:
> [sk_buff skb1]
> [atomic_t fclone_ref]
> [sk_buff skb2]
Untested patch would be :
diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index da1378a3e2c7..e39f03ea1822 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -178,6 +178,15 @@ out:
return skb;
}
+/* Layout of fast clones : [skb1][fclone_ref][skb2] */
+struct sk_buff_fclones {
+ struct sk_buff skb1;
+
+ atomic_t fclone_ref;
+
+ struct sk_buff skb2;
+};
+
/**
* __alloc_skb - allocate a network buffer
* @size: size to allocate
@@ -257,16 +266,17 @@ struct sk_buff *__alloc_skb(unsigned int size, gfp_t gfp_mask,
kmemcheck_annotate_variable(shinfo->destructor_arg);
if (flags & SKB_ALLOC_FCLONE) {
- struct sk_buff *child = skb + 1;
- atomic_t *fclone_ref = (atomic_t *) (child + 1);
+ struct sk_buff_fclones *fclones;
+
+ fclones = (struct sk_buff_fclones *)skb;
- kmemcheck_annotate_bitfield(child, flags1);
- kmemcheck_annotate_bitfield(child, flags2);
- skb->fclone = SKB_FCLONE_ORIG;
- atomic_set(fclone_ref, 1);
+ kmemcheck_annotate_bitfield(&fclones->skb2, flags1);
+ kmemcheck_annotate_bitfield(&fclones->skb2, flags2);
+ fclones->skb1.fclone = SKB_FCLONE_ORIG;
+ atomic_set(&fclones->fclone_ref, 1);
- child->fclone = SKB_FCLONE_UNAVAILABLE;
- child->pfmemalloc = pfmemalloc;
+ fclones->skb2.fclone = SKB_FCLONE_UNAVAILABLE;
+ fclones->skb2.pfmemalloc = pfmemalloc;
}
out:
return skb;
@@ -524,8 +534,7 @@ static void skb_release_data(struct sk_buff *skb)
*/
static void kfree_skbmem(struct sk_buff *skb)
{
- struct sk_buff *other;
- atomic_t *fclone_ref;
+ struct sk_buff_fclones *fclones;
switch (skb->fclone) {
case SKB_FCLONE_UNAVAILABLE:
@@ -533,22 +542,21 @@ static void kfree_skbmem(struct sk_buff *skb)
break;
case SKB_FCLONE_ORIG:
- fclone_ref = (atomic_t *) (skb + 2);
- if (atomic_dec_and_test(fclone_ref))
- kmem_cache_free(skbuff_fclone_cache, skb);
+ fclones = container_of(skb, struct sk_buff_fclones, skb1);
+ if (atomic_dec_and_test(&fclones->fclone_ref))
+ kmem_cache_free(skbuff_fclone_cache, fclones);
break;
case SKB_FCLONE_CLONE:
- fclone_ref = (atomic_t *) (skb + 1);
- other = skb - 1;
+ fclones = container_of(skb, struct sk_buff_fclones, skb2);
/* The clone portion is available for
* fast-cloning again.
*/
skb->fclone = SKB_FCLONE_UNAVAILABLE;
- if (atomic_dec_and_test(fclone_ref))
- kmem_cache_free(skbuff_fclone_cache, other);
+ if (atomic_dec_and_test(&fclones->fclone_ref))
+ kmem_cache_free(skbuff_fclone_cache, fclones);
break;
}
}
@@ -855,17 +863,16 @@ EXPORT_SYMBOL_GPL(skb_copy_ubufs);
struct sk_buff *skb_clone(struct sk_buff *skb, gfp_t gfp_mask)
{
- struct sk_buff *n;
+ struct sk_buff_fclones *fclones = (struct sk_buff_fclones *)skb;
+ struct sk_buff *n = &fclones->skb2;
if (skb_orphan_frags(skb, gfp_mask))
return NULL;
- n = skb + 1;
if (skb->fclone == SKB_FCLONE_ORIG &&
n->fclone == SKB_FCLONE_UNAVAILABLE) {
- atomic_t *fclone_ref = (atomic_t *) (n + 1);
n->fclone = SKB_FCLONE_CLONE;
- atomic_inc(fclone_ref);
+ atomic_inc(&fclones->fclone_ref);
} else {
if (skb_pfmemalloc(skb))
gfp_mask |= __GFP_MEMALLOC;
--
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