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Date: Thu, 13 Oct 2011 19:28:54 +0200
From: Eric Dumazet <eric.dumazet@...il.com>
To: Ben Hutchings <bhutchings@...arflare.com>
Cc: David Miller <davem@...emloft.net>,
netdev <netdev@...r.kernel.org>, Andi Kleen <ak@...ux.intel.com>
Subject: Re: [PATCH net-next] net: more accurate skb truesize
Le jeudi 13 octobre 2011 à 18:13 +0100, Ben Hutchings a écrit :
> On Thu, 2011-10-13 at 19:11 +0200, Eric Dumazet wrote:
> > Le jeudi 13 octobre 2011 à 17:32 +0100, Ben Hutchings a écrit :
> >
> > > Fair enough, but please add a comment explaining this.
> > >
> >
> >
> > What about :
> >
> > /* We do our best to align skb_shared_info on a separate cache
> > * line. It usually works because kmalloc(X > CACHE_BYTES) gives
> > * aligned memory blocks, unless SLUB/SLAB debug is enabled.
> > */
> > size += SKB_DATA_ALIGN(sizeof(struct skb_shared_info));
>
> Yes, that seems like a good explanation.
Thanks !
Here is the second version of the patch, including this comment.
[PATCH V2 net-next] net: more accurate skb truesize
skb truesize currently accounts for sk_buff struct and part of skb head.
kmalloc() roundings are also ignored.
Considering that skb_shared_info is larger than sk_buff, its time to
take it into account for better memory accounting.
This patch introduces SKB_TRUESIZE(X) macro to centralize various
assumptions into a single place.
At skb alloc phase, we put skb_shared_info struct at the exact end of
skb head, to allow a better use of memory (lowering number of
reallocations), since kmalloc() gives us power-of-two memory blocks.
Unless SLUB/SLUB debug is active, both skb->head and skb_shared_info are
aligned to cache lines, as before.
Note: This patch might trigger performance regressions because of
misconfigured protocol stacks, hitting per socket or global memory
limits that were previously not reached. But its a necessary step for a
more accurate memory accounting.
Signed-off-by: Eric Dumazet <eric.dumazet@...il.com>
CC: Andi Kleen <ak@...ux.intel.com>
CC: Ben Hutchings <bhutchings@...arflare.com>
---
include/linux/skbuff.h | 5 +++++
net/core/skbuff.c | 18 ++++++++++++++----
net/core/sock.c | 2 +-
net/ipv4/icmp.c | 5 ++---
net/ipv4/tcp_input.c | 14 +++++++-------
net/ipv6/icmp.c | 3 +--
net/iucv/af_iucv.c | 2 +-
net/sctp/protocol.c | 2 +-
8 files changed, 32 insertions(+), 19 deletions(-)
diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index ac6b05a..64f8695 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -46,6 +46,11 @@
#define SKB_MAX_HEAD(X) (SKB_MAX_ORDER((X), 0))
#define SKB_MAX_ALLOC (SKB_MAX_ORDER(0, 2))
+/* return minimum truesize of one skb containing X bytes of data */
+#define SKB_TRUESIZE(X) ((X) + \
+ SKB_DATA_ALIGN(sizeof(struct sk_buff)) + \
+ SKB_DATA_ALIGN(sizeof(struct skb_shared_info)))
+
/* A. Checksumming of received packets by device.
*
* NONE: device failed to checksum this packet.
diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index 5b2c5f1..a7f855d 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -184,11 +184,20 @@ struct sk_buff *__alloc_skb(unsigned int size, gfp_t gfp_mask,
goto out;
prefetchw(skb);
- size = SKB_DATA_ALIGN(size);
- data = kmalloc_node_track_caller(size + sizeof(struct skb_shared_info),
- gfp_mask, node);
+ /* We do our best to align skb_shared_info on a separate cache
+ * line. It usually works because kmalloc(X > SMP_CACHE_BYTES) gives
+ * aligned memory blocks, unless SLUB/SLAB debug is enabled.
+ * Both skb->head and skb_shared_info are cache line aligned.
+ */
+ size += SKB_DATA_ALIGN(sizeof(struct skb_shared_info));
+ data = kmalloc_node_track_caller(size, gfp_mask, node);
if (!data)
goto nodata;
+ /* kmalloc(size) might give us more room than requested.
+ * Put skb_shared_info exactly at the end of allocated zone,
+ * to allow max possible filling before reallocation.
+ */
+ size = SKB_WITH_OVERHEAD(ksize(data));
prefetchw(data + size);
/*
@@ -197,7 +206,8 @@ struct sk_buff *__alloc_skb(unsigned int size, gfp_t gfp_mask,
* the tail pointer in struct sk_buff!
*/
memset(skb, 0, offsetof(struct sk_buff, tail));
- skb->truesize = size + sizeof(struct sk_buff);
+ /* Account for allocated memory : skb + skb->head */
+ skb->truesize = SKB_TRUESIZE(size);
atomic_set(&skb->users, 1);
skb->head = data;
skb->data = data;
diff --git a/net/core/sock.c b/net/core/sock.c
index 83c462d..5a08762 100644
--- a/net/core/sock.c
+++ b/net/core/sock.c
@@ -207,7 +207,7 @@ static struct lock_class_key af_callback_keys[AF_MAX];
* not depend upon such differences.
*/
#define _SK_MEM_PACKETS 256
-#define _SK_MEM_OVERHEAD (sizeof(struct sk_buff) + 256)
+#define _SK_MEM_OVERHEAD SKB_TRUESIZE(256)
#define SK_WMEM_MAX (_SK_MEM_OVERHEAD * _SK_MEM_PACKETS)
#define SK_RMEM_MAX (_SK_MEM_OVERHEAD * _SK_MEM_PACKETS)
diff --git a/net/ipv4/icmp.c b/net/ipv4/icmp.c
index 23ef31b..ab188ae 100644
--- a/net/ipv4/icmp.c
+++ b/net/ipv4/icmp.c
@@ -1152,10 +1152,9 @@ static int __net_init icmp_sk_init(struct net *net)
net->ipv4.icmp_sk[i] = sk;
/* Enough space for 2 64K ICMP packets, including
- * sk_buff struct overhead.
+ * sk_buff/skb_shared_info struct overhead.
*/
- sk->sk_sndbuf =
- (2 * ((64 * 1024) + sizeof(struct sk_buff)));
+ sk->sk_sndbuf = 2 * SKB_TRUESIZE(64 * 1024);
/*
* Speedup sock_wfree()
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 81cae64..c1653fe 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -265,8 +265,7 @@ static inline int TCP_ECN_rcv_ecn_echo(struct tcp_sock *tp, struct tcphdr *th)
static void tcp_fixup_sndbuf(struct sock *sk)
{
- int sndmem = tcp_sk(sk)->rx_opt.mss_clamp + MAX_TCP_HEADER + 16 +
- sizeof(struct sk_buff);
+ int sndmem = SKB_TRUESIZE(tcp_sk(sk)->rx_opt.mss_clamp + MAX_TCP_HEADER);
if (sk->sk_sndbuf < 3 * sndmem) {
sk->sk_sndbuf = 3 * sndmem;
@@ -349,7 +348,7 @@ static void tcp_grow_window(struct sock *sk, struct sk_buff *skb)
static void tcp_fixup_rcvbuf(struct sock *sk)
{
struct tcp_sock *tp = tcp_sk(sk);
- int rcvmem = tp->advmss + MAX_TCP_HEADER + 16 + sizeof(struct sk_buff);
+ int rcvmem = SKB_TRUESIZE(tp->advmss + MAX_TCP_HEADER);
/* Try to select rcvbuf so that 4 mss-sized segments
* will fit to window and corresponding skbs will fit to our rcvbuf.
@@ -540,8 +539,7 @@ void tcp_rcv_space_adjust(struct sock *sk)
space /= tp->advmss;
if (!space)
space = 1;
- rcvmem = (tp->advmss + MAX_TCP_HEADER +
- 16 + sizeof(struct sk_buff));
+ rcvmem = SKB_TRUESIZE(tp->advmss + MAX_TCP_HEADER);
while (tcp_win_from_space(rcvmem) < tp->advmss)
rcvmem += 128;
space *= rcvmem;
@@ -4950,8 +4948,10 @@ static void tcp_new_space(struct sock *sk)
struct tcp_sock *tp = tcp_sk(sk);
if (tcp_should_expand_sndbuf(sk)) {
- int sndmem = max_t(u32, tp->rx_opt.mss_clamp, tp->mss_cache) +
- MAX_TCP_HEADER + 16 + sizeof(struct sk_buff);
+ int sndmem = SKB_TRUESIZE(max_t(u32,
+ tp->rx_opt.mss_clamp,
+ tp->mss_cache) +
+ MAX_TCP_HEADER);
int demanded = max_t(unsigned int, tp->snd_cwnd,
tp->reordering + 1);
sndmem *= 2 * demanded;
diff --git a/net/ipv6/icmp.c b/net/ipv6/icmp.c
index 2b59154..90868fb 100644
--- a/net/ipv6/icmp.c
+++ b/net/ipv6/icmp.c
@@ -835,8 +835,7 @@ static int __net_init icmpv6_sk_init(struct net *net)
/* Enough space for 2 64K ICMP packets, including
* sk_buff struct overhead.
*/
- sk->sk_sndbuf =
- (2 * ((64 * 1024) + sizeof(struct sk_buff)));
+ sk->sk_sndbuf = 2 * SKB_TRUESIZE(64 * 1024);
}
return 0;
diff --git a/net/iucv/af_iucv.c b/net/iucv/af_iucv.c
index c39f3a4..274d150 100644
--- a/net/iucv/af_iucv.c
+++ b/net/iucv/af_iucv.c
@@ -1819,7 +1819,7 @@ static void iucv_callback_rx(struct iucv_path *path, struct iucv_message *msg)
goto save_message;
len = atomic_read(&sk->sk_rmem_alloc);
- len += iucv_msg_length(msg) + sizeof(struct sk_buff);
+ len += SKB_TRUESIZE(iucv_msg_length(msg));
if (len > sk->sk_rcvbuf)
goto save_message;
diff --git a/net/sctp/protocol.c b/net/sctp/protocol.c
index 91784f4..61b9fca 100644
--- a/net/sctp/protocol.c
+++ b/net/sctp/protocol.c
@@ -1299,7 +1299,7 @@ SCTP_STATIC __init int sctp_init(void)
max_share = min(4UL*1024*1024, limit);
sysctl_sctp_rmem[0] = SK_MEM_QUANTUM; /* give each asoc 1 page min */
- sysctl_sctp_rmem[1] = (1500 *(sizeof(struct sk_buff) + 1));
+ sysctl_sctp_rmem[1] = 1500 * SKB_TRUESIZE(1);
sysctl_sctp_rmem[2] = max(sysctl_sctp_rmem[1], max_share);
sysctl_sctp_wmem[0] = SK_MEM_QUANTUM;
--
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