ipv6: reduce percpu needs for icmpv6msg mibs

Reading /proc/net/snmp6 on a machine with a lot of cpus is very
expensive (can be ~88000 us).

This is because ICMPV6MSG MIB uses 4096 bytes per cpu, and folding
values for all possible cpus can read 16 Mbytes of memory (32MBytes on
non x86 arches)

ICMP messages are not considered as fast path on a typical server, and
eventually few cpus handle them anyway. We can afford an atomic
operation instead of using percpu data.

This saves 4096 bytes per cpu and per network namespace.

Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 12 insertions, 3 deletions

diff --git a/include/net/ipv6.h b/include/net/ipv6.h
index a366a8a1fe23..3f0258d2ef01 100644
--- a/include/net/ipv6.h
+++ b/include/net/ipv6.h
@@ -132,6 +132,15 @@ extern struct ctl_path net_ipv6_ctl_path[];
         SNMP_INC_STATS##modifier((net)->mib.statname##_statistics, (field));\
 })
 
+/* per device and per net counters are atomic_long_t */
+#define _DEVINC_ATOMIC_ATOMIC(net, statname, idev, field)               \
+({                                                                      \
+        struct inet6_dev *_idev = (idev);                               \
+        if (likely(_idev != NULL))                                      \
+                SNMP_INC_STATS_ATOMIC_LONG((_idev)->stats.statname##dev, (field)); \
+        SNMP_INC_STATS_ATOMIC_LONG((net)->mib.statname##_statistics, (field));\
+})
+
 #define _DEVADD(net, statname, modifier, idev, field, val)              \
 ({                                                                      \
         struct inet6_dev *_idev = (idev);                               \
@@ -168,11 +177,11 @@ extern struct ctl_path net_ipv6_ctl_path[];
                 _DEVINCATOMIC(net, icmpv6, _BH, idev, field)
 
 #define ICMP6MSGOUT_INC_STATS(net, idev, field)         \
-        _DEVINCATOMIC(net, icmpv6msg, , idev, field +256)
+        _DEVINC_ATOMIC_ATOMIC(net, icmpv6msg, idev, field +256)
 #define ICMP6MSGOUT_INC_STATS_BH(net, idev, field)      \
-        _DEVINCATOMIC(net, icmpv6msg, _BH, idev, field +256)
+        _DEVINC_ATOMIC_ATOMIC(net, icmpv6msg, idev, field +256)
 #define ICMP6MSGIN_INC_STATS_BH(net, idev, field)       \
-        _DEVINCATOMIC(net, icmpv6msg, _BH, idev, field)
+        _DEVINC_ATOMIC_ATOMIC(net, icmpv6msg, idev, field)
 
 struct ip6_ra_chain {
         struct ip6_ra_chain     *next;