[PATCH net-next] tcp: change default tcp hash size

[PATCH net-next] tcp: change default tcp hash size

[Eric Dumazet]

From: Eric Dumazet <edumazet@google.com>

As time passed, available memory increased faster than number of
concurrent tcp sockets. 

As a result, a machine with 4GB of ram gets a hash table
with 524288 slots, using 8388608 bytes of memory.

Lets change that by a 16x factor (one slot for 128 KB of ram)

Even if a small machine needs a _lot_ of sockets, tcp lookups are now
very efficient, using one cache line per socket.

Signed-off-by: Eric Dumazet <edumazet@google.com>
---
 net/ipv4/tcp.c |    6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index e6eace1..1aca02c 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -3590,8 +3590,7 @@ void __init tcp_init(void)
 		alloc_large_system_hash("TCP established",
 					sizeof(struct inet_ehash_bucket),
 					thash_entries,
-					(totalram_pages >= 128 * 1024) ?
-					13 : 15,
+					17, /* one slot per 128 KB of memory */
 					0,
 					NULL,
 					&tcp_hashinfo.ehash_mask,
@@ -3607,8 +3606,7 @@ void __init tcp_init(void)
 		alloc_large_system_hash("TCP bind",
 					sizeof(struct inet_bind_hashbucket),
 					tcp_hashinfo.ehash_mask + 1,
-					(totalram_pages >= 128 * 1024) ?
-					13 : 15,
+					17, /* one slot per 128 KB of memory */
 					0,
 					&tcp_hashinfo.bhash_size,
 					NULL,

Re: [PATCH net-next] tcp: change default tcp hash size

[David Miller]

From: Eric Dumazet <eric.dumazet@gmail.com>
Date: Fri, 30 Nov 2012 12:08:52 -0800

> From: Eric Dumazet <edumazet@google.com>
> 
> As time passed, available memory increased faster than number of
> concurrent tcp sockets. 
> 
> As a result, a machine with 4GB of ram gets a hash table
> with 524288 slots, using 8388608 bytes of memory.
> 
> Lets change that by a 16x factor (one slot for 128 KB of ram)
> 
> Even if a small machine needs a _lot_ of sockets, tcp lookups are now
> very efficient, using one cache line per socket.
> 
> Signed-off-by: Eric Dumazet <edumazet@google.com>

Agreed, applied, thanks Eric.