[34-longterm 115/260] tcp: fix three tcp sysctls tuning

Paul Gortmaker
2011-01-02T07:23:24Z

From: Eric Dumazet <eric.dumazet@gmail.com>

commit c5ed63d66f24fd4f7089b5a6e087b0ce7202aa8e upstream.

As discovered by Anton Blanchard, current code to autotune
tcp_death_row.sysctl_max_tw_buckets, sysctl_tcp_max_orphans and
sysctl_max_syn_backlog makes little sense.

The bigger a page is, the less tcp_max_orphans is : 4096 on a 512GB
machine in Anton's case.

(tcp_hashinfo.bhash_size * sizeof(struct inet_bind_hashbucket))
is much bigger if spinlock debugging is on. Its wrong to select bigger
limits in this case (where kernel structures are also bigger)

bhash_size max is 65536, and we get this value even for small machines.

A better ground is to use size of ehash table, this also makes code
shorter and more obvious.

Based on a patch from Anton, and another from David.

Reported-and-tested-by: Anton Blanchard <anton@samba.org>
Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
---
net/ipv4/tcp.c | 24 +++++++-----------------
1 files changed, 7 insertions(+), 17 deletions(-)

diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index 692f424..4a638f0 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -3192,7 +3192,7 @@ void __init tcp_init(void)
{
struct sk_buff *skb = NULL;
unsigned long nr_pages, limit;
- int order, i, max_share;
+ int i, max_share, cnt;
unsigned long jiffy = jiffies;

BUILD_BUG_ON(sizeof(struct tcp_skb_cb) > sizeof(skb->cb));
@@ -3241,22 +3241,12 @@ void __init tcp_init(void)
INIT_HLIST_HEAD(&tcp_hashinfo.bhash[i].chain);
}

- /* Try to be a bit smarter and adjust defaults depending
- * on available memory.
- */
- for (order = 0; ((1 << order) << PAGE_SHIFT) <
- (tcp_hashinfo.bhash_size * sizeof(struct inet_bind_hashbucket));
- order++)
- ;
- if (order >= 4) {
- tcp_death_row.sysctl_max_tw_buckets = 180000;
- sysctl_tcp_max_orphans = 4096 << (order - 4);
- sysctl_max_syn_backlog = 1024;
- } else if (order < 3) {
- tcp_death_row.sysctl_max_tw_buckets >>= (3 - order);
- sysctl_tcp_max_orphans >>= (3 - order);
- sysctl_max_syn_backlog = 128;
- }
+
+ cnt = tcp_hashinfo.ehash_mask + 1;
+
+ tcp_death_row.sysctl_max_tw_buckets = cnt / 2;
+ sysctl_tcp_max_orphans = cnt / 2;
+ sysctl_max_syn_backlog = max(128, cnt / 256);

/* Set the pressure threshold to be a fraction of global memory that
* is up to 1/2 at 256 MB, decreasing toward zero with the amount of
--
1.7.3.3