tcp: fix three tcp sysctls tuning (c5ed63d6) · Commits · 戴 / test

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>

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

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