Re: [PATCH] limit rt cache size

[David Miller <davem@davemloft.net>]

From: Andi Kleen <ak@suse.de>
Date: Tue, 8 Aug 2006 07:11:06 +0200

> The hash sizing code needs far more tweaks. iirc it can still
> allocate several GB hash tables on large memory systems (i've seen
> that once in the boot log of a 2TB system).  Even on smaller systems
> it is usually too much.

There is already a limit parameter to alloc_large_system_hash(), the
fact that the routing cache passes in zero (which causes the limit to
be 1/16 of all system memory) is just a bug. :-)

In passing this immediately this suggests a fix to alloc_large_system_hash,
in that when limit is given as 0, it should follow the same rules for
HASH_HIGHME which are applied to the "scale" arg.  It currently goes:

	if (max == 0) {
		max = ((unsigned long long)nr_all_pages << PAGE_SHIFT) >> 4;
		do_div(max, bucketsize);
	}

Whereas it should probably go:

	if (max == 0) {
		max = (flags & HASH_HIGHMEM) ? nr_all_pages : nr_kernel_pages;
		max = (max << PAGE_SHIFT) >> 4;
		do_div(max, bucketsize);
	}

or something like that.