maxusers (thus mbuf etc.) autotuning capped at 384

Hi,

We have 'maxusers' tunable which affects many other tunables, e.g. number of
network mbuf/clusters which is often too low on current machines.

There is code in sys/kern/subr_param.c:

        if (maxusers == 0) {
	        maxusers = physpages / (2 * 1024 * 1024 / PAGE_SIZE);
		if (maxusers < 32)
		        maxusers = 32;
		if (maxusers > 384)
		        maxusers = 384;
	}

It was capped to 384 for i386 KVM size limits in r89769, so that amd64, not
constrained to 1Gb KVA, suffers from this. I suspect that 384 may be wrong even
for i386 today, but let's be conservative and limit maxusers to 384 per 1 Gb of
KVM, like this:

#define _MAX_MAXUSERS           (((VM_MAX_KERNEL_ADDRESS - \
    KERNBASE) / (8 * 1024 * 1024)) * 3) 

        if (maxusers == 0) {
	        maxusers = physpages / (2 * 1024 * 1024 / PAGE_SIZE);
		if (maxusers < 32)
		        maxusers = 32;
		if (maxusers > _MAX_MAXUSERS)
		        maxusers = _MAX_MAXUSERS;
	}
#undef _MAX_MAXUSERS

Any better ideas?

-- 
WBR, Vadim Goncharov. ICQ#166852181       mailto:vadim_nuclight_at_mail.ru
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