Re: [patch 0/7] [RFC] SLUB: Improve allocpercpu to reduce per cpuaccess overhead

[David Miller]

From: Christoph Lameter <clameter@xxxxxxx>
Date: Thu, 1 Nov 2007 15:15:39 -0700 (PDT)

> After boot is complete we allow the reduction of the size of the per cpu 
> areas . Lets say we only need 128k per cpu. Then the remaining pages will
> be returned to the page allocator.

You don't know how much you will need.  I exhausted the limit on
sparc64 very late in the boot process when the last few userland
services were starting up.

And if I subsequently bring up 100,000 IP tunnels, it will exhaust the
per-cpu allocation area.

You have to make it fully dynamic, there is no way around it.
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