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skbuff: introduce {,__}napi_build_skb() which reuses NAPI cache heads

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Instead of just bulk-flushing skbuff_heads queued up through
napi_consume_skb() or __kfree_skb_defer(), try to reuse them
on allocation path.
If the cache is empty on allocation, bulk-allocate the first
16 elements, which is more efficient than per-skb allocation.
If the cache is full on freeing, bulk-wipe the second half of
the cache (32 elements).
This also includes custom KASAN poisoning/unpoisoning to be
double sure there are no use-after-free cases.

To not change current behaviour, introduce a new function,
napi_build_skb(), to optionally use a new approach later
in drivers.

Note on selected bulk size, 16:
 - this equals to XDP_BULK_QUEUE_SIZE, DEV_MAP_BULK_SIZE
   and especially VETH_XDP_BATCH, which is also used to
   bulk-allocate skbuff_heads and was tested on powerful
   setups;
 - this also showed the best performance in the actual
   test series (from the array of {8, 16, 32}).

Suggested-by: Edward Cree <ecree.xilinx@gmail.com> # Divide on two halves
Suggested-by: Eric Dumazet <edumazet@google.com>   # KASAN poisoning
Cc: Dmitry Vyukov <dvyukov@google.com>             # Help with KASAN
Cc: Paolo Abeni <pabeni@redhat.com>                # Reduced batch size
Signed-off-by: Alexander Lobakin <alobakin@pm.me>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Alexander Lobakin 2021-02-13 14:12:25 +00:00 committed by David S. Miller
parent 50fad4b543
commit f450d539c0
2 changed files with 83 additions and 13 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
include/linux/skbuff.h
View File

@ -1087,6 +1087,8 @@ struct sk_buff *build_skb(void *data, unsigned int frag_size);
struct sk_buff *build_skb_around(struct sk_buff *skb,
void *data, unsigned int frag_size);
struct sk_buff *napi_build_skb(void *data, unsigned int frag_size);
/**
* alloc_skb - allocate a network buffer
* @size: size to allocate

94
net/core/skbuff.c
View File

@ -120,6 +120,8 @@ static void skb_under_panic(struct sk_buff *skb, unsigned int sz, void *addr)
}
#define NAPI_SKB_CACHE_SIZE 64
#define NAPI_SKB_CACHE_BULK 16
#define NAPI_SKB_CACHE_HALF (NAPI_SKB_CACHE_SIZE / 2)
struct napi_alloc_cache {
struct page_frag_cache page;
@ -164,6 +166,25 @@ void *__netdev_alloc_frag_align(unsigned int fragsz, unsigned int align_mask)
}
EXPORT_SYMBOL(__netdev_alloc_frag_align);
static struct sk_buff *napi_skb_cache_get(void)
{
struct napi_alloc_cache *nc = this_cpu_ptr(&napi_alloc_cache);
struct sk_buff *skb;
if (unlikely(!nc->skb_count))
nc->skb_count = kmem_cache_alloc_bulk(skbuff_head_cache,
GFP_ATOMIC,
NAPI_SKB_CACHE_BULK,
nc->skb_cache);
if (unlikely(!nc->skb_count))
return NULL;
skb = nc->skb_cache[--nc->skb_count];
kasan_unpoison_object_data(skbuff_head_cache, skb);
return skb;
}
/* Caller must provide SKB that is memset cleared */
static void __build_skb_around(struct sk_buff *skb, void *data,
unsigned int frag_size)
@ -265,6 +286,53 @@ struct sk_buff *build_skb_around(struct sk_buff *skb,
}
EXPORT_SYMBOL(build_skb_around);
/**
* __napi_build_skb - build a network buffer
* @data: data buffer provided by caller
* @frag_size: size of data, or 0 if head was kmalloced
*
* Version of __build_skb() that uses NAPI percpu caches to obtain
* skbuff_head instead of inplace allocation.
*
* Returns a new &sk_buff on success, %NULL on allocation failure.
*/
static struct sk_buff *__napi_build_skb(void *data, unsigned int frag_size)
{
struct sk_buff *skb;
skb = napi_skb_cache_get();
if (unlikely(!skb))
return NULL;
memset(skb, 0, offsetof(struct sk_buff, tail));
__build_skb_around(skb, data, frag_size);
return skb;
}
/**
* napi_build_skb - build a network buffer
* @data: data buffer provided by caller
* @frag_size: size of data, or 0 if head was kmalloced
*
* Version of __napi_build_skb() that takes care of skb->head_frag
* and skb->pfmemalloc when the data is a page or page fragment.
*
* Returns a new &sk_buff on success, %NULL on allocation failure.
*/
struct sk_buff *napi_build_skb(void *data, unsigned int frag_size)
{
struct sk_buff *skb = __napi_build_skb(data, frag_size);
if (likely(skb) && frag_size) {
skb->head_frag = 1;
skb_propagate_pfmemalloc(virt_to_head_page(data), skb);
}
return skb;
}
EXPORT_SYMBOL(napi_build_skb);
/*
* kmalloc_reserve is a wrapper around kmalloc_node_track_caller that tells
* the caller if emergency pfmemalloc reserves are being used. If it is and
@ -838,31 +906,31 @@ void __consume_stateless_skb(struct sk_buff *skb)
kfree_skbmem(skb);
}
static inline void _kfree_skb_defer(struct sk_buff *skb)
static void napi_skb_cache_put(struct sk_buff *skb)
{
struct napi_alloc_cache *nc = this_cpu_ptr(&napi_alloc_cache);
u32 i;
/* drop skb->head and call any destructors for packet */
skb_release_all(skb);
/* record skb to CPU local list */
kasan_poison_object_data(skbuff_head_cache, skb);
nc->skb_cache[nc->skb_count++] = skb;
#ifdef CONFIG_SLUB
/* SLUB writes into objects when freeing */
prefetchw(skb);
#endif
/* flush skb_cache if it is filled */
if (unlikely(nc->skb_count == NAPI_SKB_CACHE_SIZE)) {
kmem_cache_free_bulk(skbuff_head_cache, NAPI_SKB_CACHE_SIZE,
nc->skb_cache);
nc->skb_count = 0;
for (i = NAPI_SKB_CACHE_HALF; i < NAPI_SKB_CACHE_SIZE; i++)
kasan_unpoison_object_data(skbuff_head_cache,
nc->skb_cache[i]);
kmem_cache_free_bulk(skbuff_head_cache, NAPI_SKB_CACHE_HALF,
nc->skb_cache + NAPI_SKB_CACHE_HALF);
nc->skb_count = NAPI_SKB_CACHE_HALF;
}
}
void __kfree_skb_defer(struct sk_buff *skb)
{
_kfree_skb_defer(skb);
napi_skb_cache_put(skb);
}
void napi_consume_skb(struct sk_buff *skb, int budget)
@ -887,7 +955,7 @@ void napi_consume_skb(struct sk_buff *skb, int budget)
return;
}
_kfree_skb_defer(skb);
napi_skb_cache_put(skb);
}
EXPORT_SYMBOL(napi_consume_skb);