From d3836f21b0af5513ef55701dd3f50b8c42e44c7a Mon Sep 17 00:00:00 2001 From: Eric Dumazet Date: Fri, 27 Apr 2012 00:33:38 +0000 Subject: [PATCH] net: allow skb->head to be a page fragment MIME-Version: 1.0 Content-Type: text/plain; charset=utf8 Content-Transfer-Encoding: 8bit skb->head is currently allocated from kmalloc(). This is convenient but has the drawback the data cannot be converted to a page fragment if needed. We have three spots were it hurts : 1) GRO aggregation When a linear skb must be appended to another skb, GRO uses the frag_list fallback, very inefficient since we keep all struct sk_buff around. So drivers enabling GRO but delivering linear skbs to network stack aren't enabling full GRO power. 2) splice(socket -> pipe). We must copy the linear part to a page fragment. This kind of defeats splice() purpose (zero copy claim) 3) TCP coalescing. Recently introduced, this permits to group several contiguous segments into a single skb. This shortens queue lengths and save kernel memory, and greatly reduce probabilities of TCP collapses. This coalescing doesnt work on linear skbs (or we would need to copy data, this would be too slow) Given all these issues, the following patch introduces the possibility of having skb->head be a fragment in itself. We use a new skb flag, skb->head_frag to carry this information. build_skb() is changed to accept a frag_size argument. Drivers willing to provide a page fragment instead of kmalloc() data will set a non zero value, set to the fragment size. Then, on situations we need to convert the skb head to a frag in itself, we can check if skb->head_frag is set and avoid the copies or various fallbacks we have. This means drivers currently using frags could be updated to avoid the current skb->head allocation and reduce their memory footprint (aka skb truesize). (thats 512 or 1024 bytes saved per skb). This also makes bpf/netfilter faster since the 'first frag' will be part of skb linear part, no need to copy data. Signed-off-by: Eric Dumazet Cc: Ilpo Järvinen Cc: Herbert Xu Cc: Maciej Żenczykowski Cc: Neal Cardwell Cc: Tom Herbert Cc: Jeff Kirsher Cc: Ben Hutchings Cc: Matt Carlson Cc: Michael Chan Signed-off-by: David S. Miller --- drivers/net/ethernet/broadcom/bnx2.c | 2 +- .../net/ethernet/broadcom/bnx2x/bnx2x_cmn.c | 4 ++-- drivers/net/ethernet/broadcom/tg3.c | 2 +- include/linux/skbuff.h | 5 ++-- net/core/skbuff.c | 24 ++++++++++++++----- 5 files changed, 25 insertions(+), 12 deletions(-) diff --git a/drivers/net/ethernet/broadcom/bnx2.c b/drivers/net/ethernet/broadcom/bnx2.c index ab55979b3756..ac7b74488531 100644 --- a/drivers/net/ethernet/broadcom/bnx2.c +++ b/drivers/net/ethernet/broadcom/bnx2.c @@ -3006,7 +3006,7 @@ error: dma_unmap_single(&bp->pdev->dev, dma_addr, bp->rx_buf_use_size, PCI_DMA_FROMDEVICE); - skb = build_skb(data); + skb = build_skb(data, 0); if (!skb) { kfree(data); goto error; diff --git a/drivers/net/ethernet/broadcom/bnx2x/bnx2x_cmn.c b/drivers/net/ethernet/broadcom/bnx2x/bnx2x_cmn.c index afa6cbb6b193..be0e90382d9e 100644 --- a/drivers/net/ethernet/broadcom/bnx2x/bnx2x_cmn.c +++ b/drivers/net/ethernet/broadcom/bnx2x/bnx2x_cmn.c @@ -513,7 +513,7 @@ static inline void bnx2x_tpa_stop(struct bnx2x *bp, struct bnx2x_fastpath *fp, dma_unmap_single(&bp->pdev->dev, dma_unmap_addr(rx_buf, mapping), fp->rx_buf_size, DMA_FROM_DEVICE); if (likely(new_data)) - skb = build_skb(data); + skb = build_skb(data, 0); if (likely(skb)) { #ifdef BNX2X_STOP_ON_ERROR @@ -721,7 +721,7 @@ int bnx2x_rx_int(struct bnx2x_fastpath *fp, int budget) dma_unmap_addr(rx_buf, mapping), fp->rx_buf_size, DMA_FROM_DEVICE); - skb = build_skb(data); + skb = build_skb(data, 0); if (unlikely(!skb)) { kfree(data); fp->eth_q_stats.rx_skb_alloc_failed++; diff --git a/drivers/net/ethernet/broadcom/tg3.c b/drivers/net/ethernet/broadcom/tg3.c index 0c3e7c70ffbc..d481b0a99847 100644 --- a/drivers/net/ethernet/broadcom/tg3.c +++ b/drivers/net/ethernet/broadcom/tg3.c @@ -5844,7 +5844,7 @@ static int tg3_rx(struct tg3_napi *tnapi, int budget) pci_unmap_single(tp->pdev, dma_addr, skb_size, PCI_DMA_FROMDEVICE); - skb = build_skb(data); + skb = build_skb(data, 0); if (!skb) { kfree(data); goto drop_it_no_recycle; diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h index 4a656b51825e..9d28a22a8554 100644 --- a/include/linux/skbuff.h +++ b/include/linux/skbuff.h @@ -470,7 +470,8 @@ struct sk_buff { __u8 wifi_acked_valid:1; __u8 wifi_acked:1; __u8 no_fcs:1; - /* 9/11 bit hole (depending on ndisc_nodetype presence) */ + __u8 head_frag:1; + /* 8/10 bit hole (depending on ndisc_nodetype presence) */ kmemcheck_bitfield_end(flags2); #ifdef CONFIG_NET_DMA @@ -562,7 +563,7 @@ 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); -extern struct sk_buff *build_skb(void *data); +extern struct sk_buff *build_skb(void *data, unsigned int frag_size); static inline struct sk_buff *alloc_skb(unsigned int size, gfp_t priority) { diff --git a/net/core/skbuff.c b/net/core/skbuff.c index 2342a7250391..effa75d0e318 100644 --- a/net/core/skbuff.c +++ b/net/core/skbuff.c @@ -245,6 +245,7 @@ EXPORT_SYMBOL(__alloc_skb); /** * build_skb - build a network buffer * @data: data buffer provided by caller + * @frag_size: size of fragment, or 0 if head was kmalloced * * Allocate a new &sk_buff. Caller provides space holding head and * skb_shared_info. @data must have been allocated by kmalloc() @@ -258,20 +259,21 @@ EXPORT_SYMBOL(__alloc_skb); * before giving packet to stack. * RX rings only contains data buffers, not full skbs. */ -struct sk_buff *build_skb(void *data) +struct sk_buff *build_skb(void *data, unsigned int frag_size) { struct skb_shared_info *shinfo; struct sk_buff *skb; - unsigned int size; + unsigned int size = frag_size ? : ksize(data); skb = kmem_cache_alloc(skbuff_head_cache, GFP_ATOMIC); if (!skb) return NULL; - size = ksize(data) - SKB_DATA_ALIGN(sizeof(struct skb_shared_info)); + size -= SKB_DATA_ALIGN(sizeof(struct skb_shared_info)); memset(skb, 0, offsetof(struct sk_buff, tail)); skb->truesize = SKB_TRUESIZE(size); + skb->head_frag = frag_size != 0; atomic_set(&skb->users, 1); skb->head = data; skb->data = data; @@ -376,6 +378,14 @@ static void skb_clone_fraglist(struct sk_buff *skb) skb_get(list); } +static void skb_free_head(struct sk_buff *skb) +{ + if (skb->head_frag) + put_page(virt_to_head_page(skb->head)); + else + kfree(skb->head); +} + static void skb_release_data(struct sk_buff *skb) { if (!skb->cloned || @@ -402,7 +412,7 @@ static void skb_release_data(struct sk_buff *skb) if (skb_has_frag_list(skb)) skb_drop_fraglist(skb); - kfree(skb->head); + skb_free_head(skb); } } @@ -644,6 +654,7 @@ static struct sk_buff *__skb_clone(struct sk_buff *n, struct sk_buff *skb) C(tail); C(end); C(head); + C(head_frag); C(data); C(truesize); atomic_set(&n->users, 1); @@ -940,7 +951,7 @@ int pskb_expand_head(struct sk_buff *skb, int nhead, int ntail, fastpath = atomic_read(&skb_shinfo(skb)->dataref) == delta; } - if (fastpath && + if (fastpath && !skb->head_frag && size + sizeof(struct skb_shared_info) <= ksize(skb->head)) { memmove(skb->head + size, skb_shinfo(skb), offsetof(struct skb_shared_info, @@ -967,7 +978,7 @@ int pskb_expand_head(struct sk_buff *skb, int nhead, int ntail, offsetof(struct skb_shared_info, frags[skb_shinfo(skb)->nr_frags])); if (fastpath) { - kfree(skb->head); + skb_free_head(skb); } else { /* copy this zero copy skb frags */ if (skb_shinfo(skb)->tx_flags & SKBTX_DEV_ZEROCOPY) { @@ -985,6 +996,7 @@ int pskb_expand_head(struct sk_buff *skb, int nhead, int ntail, off = (data + nhead) - skb->head; skb->head = data; + skb->head_frag = 0; adjust_others: skb->data += off; #ifdef NET_SKBUFF_DATA_USES_OFFSET -- 2.30.2