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authorEric Dumazet <edumazet@google.com>2023-02-06 20:31:03 +0300
committerJakub Kicinski <kuba@kernel.org>2023-02-07 21:59:58 +0300
commitbf9f1baa279f0758dc2297080360c5a616843927 (patch)
tree63eee2d53a03648d9d0aeb3a2535315a0dc6bf25 /net/core
parent5c0e820cbbbe2d1c4cea5cd2bfc1302c123436df (diff)
downloadlinux-bf9f1baa279f0758dc2297080360c5a616843927.tar.xz
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 dbae2b062824 ("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>
Diffstat (limited to 'net/core')
-rw-r--r--net/core/skbuff.c72
1 files changed, 67 insertions, 5 deletions
diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index c1232837cd0c..bdb1e015e32b 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -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);