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Date: Fri, 03 Aug 2012 11:53:58 +0200
From: Eric Dumazet <eric.dumazet@...il.com>
To: David Miller <davem@...emloft.net>
Cc: sakiwit@...il.com, netdev@...r.kernel.org
Subject: Re: [PATCH] ipv4: remove parentheses in return statement
On Fri, 2012-08-03 at 02:22 -0700, David Miller wrote:
> From: Eric Dumazet <eric.dumazet@...il.com>
> Date: Fri, 03 Aug 2012 11:19:44 +0200
>
> > On Fri, 2012-08-03 at 01:43 -0600, Jean Sacren wrote:
> >
> >> @@ -106,8 +106,8 @@ static inline unsigned int inet_addr_hash(struct net *net, __be32 addr)
> >> {
> >> u32 val = (__force u32) addr ^ hash_ptr(net, 8);
> >>
> >> - return ((val ^ (val >> 8) ^ (val >> 16) ^ (val >> 24)) &
> >> - (IN4_ADDR_HSIZE - 1));
> >> + return (val ^ (val >> 8) ^ (val >> 16) ^ (val >> 24)) &
> >> + (IN4_ADDR_HSIZE - 1);
> >> }
> >
> > BTW This should use a faster implementation, I'll send a patch when
> > net-next is opened.
>
> There seems to be a few spots where we want the pointer "as a 32-bit
> integer" for hashing. We were discussing arp_hashfn() and ndisc_hashfn()
> the other day.
>
> It should basically do something like:
>
> (u32) ((u64)ptr >> 32 | ((u32) ptr))
>
> on 64-bit and simply (u32)(ptr) on 32-bit.
We already have such thing in fact : net_hash_mix() which returns 0 if
NS are not configured.
(hash_ptr(net,8) is really overkill on 64bit arches)
High order bits on "struct net *" have absolutely no entropy, unless you
have a monster machine (more than 256 GB of ram)
This is the patch I prepared :
diff --git a/net/ipv4/devinet.c b/net/ipv4/devinet.c
index 44bf82e..b9753ab 100644
--- a/net/ipv4/devinet.c
+++ b/net/ipv4/devinet.c
@@ -94,25 +94,22 @@ static const struct nla_policy ifa_ipv4_policy[IFA_MAX+1] = {
[IFA_LABEL] = { .type = NLA_STRING, .len = IFNAMSIZ - 1 },
};
-/* inet_addr_hash's shifting is dependent upon this IN4_ADDR_HSIZE
- * value. So if you change this define, make appropriate changes to
- * inet_addr_hash as well.
- */
-#define IN4_ADDR_HSIZE 256
+#define IN4_ADDR_HSIZE_SHIFT 8
+#define IN4_ADDR_HSIZE (1U << IN4_ADDR_HSIZE_SHIFT)
+
static struct hlist_head inet_addr_lst[IN4_ADDR_HSIZE];
static DEFINE_SPINLOCK(inet_addr_hash_lock);
-static inline unsigned int inet_addr_hash(struct net *net, __be32 addr)
+static u32 inet_addr_hash(struct net *net, __be32 addr)
{
- u32 val = (__force u32) addr ^ hash_ptr(net, 8);
+ u32 val = (__force u32) addr ^ net_hash_mix(net);
- return ((val ^ (val >> 8) ^ (val >> 16) ^ (val >> 24)) &
- (IN4_ADDR_HSIZE - 1));
+ return hash_32(val, IN4_ADDR_HSIZE_SHIFT);
}
static void inet_hash_insert(struct net *net, struct in_ifaddr *ifa)
{
- unsigned int hash = inet_addr_hash(net, ifa->ifa_local);
+ u32 hash = inet_addr_hash(net, ifa->ifa_local);
spin_lock(&inet_addr_hash_lock);
hlist_add_head_rcu(&ifa->hash, &inet_addr_lst[hash]);
@@ -136,18 +133,18 @@ static void inet_hash_remove(struct in_ifaddr *ifa)
*/
struct net_device *__ip_dev_find(struct net *net, __be32 addr, bool devref)
{
- unsigned int hash = inet_addr_hash(net, addr);
+ u32 hash = inet_addr_hash(net, addr);
struct net_device *result = NULL;
struct in_ifaddr *ifa;
struct hlist_node *node;
rcu_read_lock();
hlist_for_each_entry_rcu(ifa, node, &inet_addr_lst[hash], hash) {
- struct net_device *dev = ifa->ifa_dev->dev;
-
- if (!net_eq(dev_net(dev), net))
- continue;
if (ifa->ifa_local == addr) {
+ struct net_device *dev = ifa->ifa_dev->dev;
+
+ if (!net_eq(dev_net(dev), net)
+ continue;
result = dev;
break;
}
--
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