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Commit c5ed63d6 authored by Eric Dumazet's avatar Eric Dumazet Committed by David S. Miller
Browse files

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: default avatarAnton Blanchard <anton@samba.org>
Signed-off-by: default avatarEric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent ad1af0fe

net/ipv4/tcp.c

+7 −17
Original line number Diff line number Diff line
@@ -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