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net: add dedicated kmem_cache for typical/small skb->head 

Recent removal of ksize() in alloc_skb() increased
performance because we no longer read
the associated struct page.

We have an equivalent cost at kfree_skb() time.

kfree(skb->head) has to access a struct page,
often cold in cpu caches to get the owning
struct kmem_cache.

Considering that many allocations are small (at least for TCP ones)
we can have our own kmem_cache to avoid the cache line miss.

This also saves memory because these small heads
are no longer padded to 1024 bytes.

CONFIG_SLUB=y
$ grep skbuff_small_head /proc/slabinfo
skbuff_small_head   2907   2907    640   51    8 : tunables    0    0    0 : slabdata     57     57      0

CONFIG_SLAB=y
$ grep skbuff_small_head /proc/slabinfo
skbuff_small_head    607    624    640    6    1 : tunables   54   27    8 : slabdata    104    104      5

Notes:

- After Kees Cook patches and this one, we might
  be able to revert commit
  dbae2b0628 ("net: skb: introduce and use a single page frag cache")
  because GRO_MAX_HEAD is also small.

- This patch is a NOP for CONFIG_SLOB=y builds.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Acked-by: Soheil Hassas Yeganeh <soheil@google.com>
Acked-by: Paolo Abeni <pabeni@redhat.com>
Reviewed-by: Alexander Duyck <alexanderduyck@fb.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
This commit is contained in:
Eric Dumazet 2023-02-06 17:31:03 +00:00 committed by Jakub Kicinski
parent 5c0e820cbb
commit bf9f1baa27
1 changed files with 67 additions and 5 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

72
net/core/skbuff.c
View File

@ -89,6 +89,34 @@ static struct kmem_cache *skbuff_fclone_cache __ro_after_init;
#ifdef CONFIG_SKB_EXTENSIONS
static struct kmem_cache *skbuff_ext_cache __ro_after_init;
#endif
/* skb_small_head_cache and related code is only supported
* for CONFIG_SLAB and CONFIG_SLUB.
* As soon as SLOB is removed from the kernel, we can clean up this.
*/
#if !defined(CONFIG_SLOB)
# define HAVE_SKB_SMALL_HEAD_CACHE 1
#endif
#ifdef HAVE_SKB_SMALL_HEAD_CACHE
static struct kmem_cache *skb_small_head_cache __ro_after_init;
#define SKB_SMALL_HEAD_SIZE SKB_HEAD_ALIGN(MAX_TCP_HEADER)
/* We want SKB_SMALL_HEAD_CACHE_SIZE to not be a power of two.
* This should ensure that SKB_SMALL_HEAD_HEADROOM is a unique
* size, and we can differentiate heads from skb_small_head_cache
* vs system slabs by looking at their size (skb_end_offset()).
*/
#define SKB_SMALL_HEAD_CACHE_SIZE \
(is_power_of_2(SKB_SMALL_HEAD_SIZE) ? \
(SKB_SMALL_HEAD_SIZE + L1_CACHE_BYTES) : \
SKB_SMALL_HEAD_SIZE)
#define SKB_SMALL_HEAD_HEADROOM \
SKB_WITH_OVERHEAD(SKB_SMALL_HEAD_CACHE_SIZE)
#endif /* HAVE_SKB_SMALL_HEAD_CACHE */
int sysctl_max_skb_frags __read_mostly = MAX_SKB_FRAGS;
EXPORT_SYMBOL(sysctl_max_skb_frags);
@ -486,6 +514,23 @@ static void *kmalloc_reserve(unsigned int *size, gfp_t flags, int node,
void *obj;
obj_size = SKB_HEAD_ALIGN(*size);
#ifdef HAVE_SKB_SMALL_HEAD_CACHE
if (obj_size <= SKB_SMALL_HEAD_CACHE_SIZE &&
!(flags & KMALLOC_NOT_NORMAL_BITS)) {
/* skb_small_head_cache has non power of two size,
* likely forcing SLUB to use order-3 pages.
* We deliberately attempt a NOMEMALLOC allocation only.
*/
obj = kmem_cache_alloc_node(skb_small_head_cache,
flags | __GFP_NOMEMALLOC | __GFP_NOWARN,
node);
if (obj) {
*size = SKB_SMALL_HEAD_CACHE_SIZE;
goto out;
}
}
#endif
*size = obj_size = kmalloc_size_roundup(obj_size);
/*
* Try a regular allocation, when that fails and we're not entitled
@ -805,6 +850,16 @@ static bool skb_pp_recycle(struct sk_buff *skb, void *data)
return page_pool_return_skb_page(virt_to_page(data));
}
static void skb_kfree_head(void *head, unsigned int end_offset)
{
#ifdef HAVE_SKB_SMALL_HEAD_CACHE
if (end_offset == SKB_SMALL_HEAD_HEADROOM)
kmem_cache_free(skb_small_head_cache, head);
else
#endif
kfree(head);
}
static void skb_free_head(struct sk_buff *skb)
{
unsigned char *head = skb->head;
@ -814,7 +869,7 @@ static void skb_free_head(struct sk_buff *skb)
return;
skb_free_frag(head);
} else {
kfree(head);
skb_kfree_head(head, skb_end_offset(skb));
}
}
@ -1997,7 +2052,7 @@ int pskb_expand_head(struct sk_buff *skb, int nhead, int ntail,
return 0;
nofrags:
kfree(data);
skb_kfree_head(data, size);
nodata:
return -ENOMEM;
}
@ -4634,6 +4689,13 @@ void __init skb_init(void)
0,
SLAB_HWCACHE_ALIGN|SLAB_PANIC,
NULL);
#ifdef HAVE_SKB_SMALL_HEAD_CACHE
skb_small_head_cache = kmem_cache_create("skbuff_small_head",
SKB_SMALL_HEAD_CACHE_SIZE,
0,
SLAB_HWCACHE_ALIGN | SLAB_PANIC,
NULL);
#endif
skb_extensions_init();
}
@ -6298,7 +6360,7 @@ static int pskb_carve_inside_header(struct sk_buff *skb, const u32 off,
if (skb_cloned(skb)) {
/* drop the old head gracefully */
if (skb_orphan_frags(skb, gfp_mask)) {
kfree(data);
skb_kfree_head(data, size);
return -ENOMEM;
}
for (i = 0; i < skb_shinfo(skb)->nr_frags; i++)
@ -6406,7 +6468,7 @@ static int pskb_carve_inside_nonlinear(struct sk_buff *skb, const u32 off,
memcpy((struct skb_shared_info *)(data + size),
skb_shinfo(skb), offsetof(struct skb_shared_info, frags[0]));
if (skb_orphan_frags(skb, gfp_mask)) {
kfree(data);
skb_kfree_head(data, size);
return -ENOMEM;
}
shinfo = (struct skb_shared_info *)(data + size);
@ -6442,7 +6504,7 @@ static int pskb_carve_inside_nonlinear(struct sk_buff *skb, const u32 off,
/* skb_frag_unref() is not needed here as shinfo->nr_frags = 0. */
if (skb_has_frag_list(skb))
kfree_skb_list(skb_shinfo(skb)->frag_list);
kfree(data);
skb_kfree_head(data, size);
return -ENOMEM;
}
skb_release_data(skb, SKB_CONSUMED);