tcp: fix three tcp sysctls tuning

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>

1 files changed, 7 insertions, 17 deletions

diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index 197b9b77fa3e..e2add5ff9cb1 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -3209,7 +3209,7 @@ 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));
@@ -3258,22 +3258,12 @@ 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