Re: SLUB: Use ilog2 instead of series of constant comparisons.

[Andrew Morton <akpm@linux-foundation.org>]

On Wed, 6 Jun 2007 11:36:07 -0700 (PDT) Christoph Lameter <clameter@sgi.com> wrote:

> On Wed, 6 Jun 2007, Andrew Morton wrote:
> 
> > This caused test.kernel.org's power4 build to blow up:
> > 
> > http://test.kernel.org/abat/93315/debug/test.log.0
> > 
> > fs/built-in.o(.text+0x148420): In function `.CalcNTLMv2_partial_mac_key':
> > : undefined reference to `.____ilog2_NaN'
> 
> Hmmm... Weird message that does not allow too much analysis.
> The __ilog2_NaN comes about if 0 or a negative number is passed to ilog. 
> There is no way for that to happen since we check for KMALLOC_MIN_SIZE 
> and KMALLOC_MAX_SIZE in kmalloc_index() and an unsigned value is used.
> 
> There is also nothing special in CalcNTLMv2_partial_mac_key(). Two 
> kmallocs of 33 bytes and 132 bytes each.

Yes, the code all looks OK.  I suspect this is another case of the compiler
failing to remove unreachable stuff.

> Buggy compiler (too much stress on constant folding)? Or hardware? Can we 
> rerun the test?

It happened multiple times:
http://test.kernel.org/functional/pSeries-101_2.html

I'm sure there's a way of extracting the compiler version out of
test.kernel.org but I can't see it there.  Andy, maybe we should toss a gcc
--version in there or something?


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