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From: Roland Dreier <rdreier@cisco.com>
To: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Subject: Re: [PATCH 04/10] 8xx: Always pin kernel instruction TLB
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Date: Sat, 14 Nov 2009 22:49:47 -0800
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Cc: Scott Wood <scottwood@freescale.com>,
	"linuxppc-dev@ozlabs.org" <linuxppc-dev@ozlabs.org>,
	Rex Feany <RFeany@mrv.com>
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 > > How to make better use of the remaining ITLB slots is tricky.
 > > Somehow one would want to map at lest one to modules but I cannot see how.
 > 
 > No. If you use modules, you pay the price. Sane embedded solutions
 > running in "tight" environments don't use modules :-) No point pinning
 > TLB entries on the vmalloc space, really.

Long ago (2.4 days I think) when using modules on ppc 4xx we hacked the
module_alloc function (or whatever it was called back then) to allocate
space in the kernel pinned TLB instead of using vmalloc.  Gave something
like a 2x speedup for module code, since the 4xx TLB is so small and the
miss handling is so expensive.  I assume it should still be possible to
do a similar hack with current kernels.

 - R.