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@gmail.com>
CC: Andi Kleen <ak@linux.intel.com>
CC: Ben Hutchings <bhutchings@solarflare.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index ac6b05a..64f8695 100644 (file)
--- 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 (file)
--- 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 (file)
--- 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 (file)
--- 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 (file)
--- 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 (file)
--- 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 (file)
--- 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 (file)
--- 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;