Re: [Bug #13319] Page allocation failures with b43 and p54usb

On Mon, 29 Jun 2009, Larry Finger wrote:

I'd disagree with disabling slub debugging by default for caches where
oo_order(s->min) increases as the result of using it. This particular
page allocation failure is happening for, presumably, kmalloc-4096, and
the system has 4K pages. Disabling debugging for that cache (and any of
its aliases) implicitly will lead to errors going undiagnosed as a result.

If the current behavior is not changed, I will be forced to disable
SLUB debugging, which will explicitly lead to errors that are
undiagnosed.

You're buying debugging support at the cost of increased memory
consumption when you enable CONFIG_SLUB_DEBUG_ON and that's causing the
page allocation failures because of fragmentation. To reduce the minimum
order required for caches such as kmalloc-4096, you'd have to disable
debugging for that particular cache. It's my opinion that such a
configuration should not be the default, however.

You could argue adding `slub_debug=-,kmalloc-4096' support from the
command line, but CONFIG_SLUB_DEBUG_ON should not change its well-defined
purpose of enabling debugging on all slab caches. Otherwise the rest of
us would be forced to add `slub_debug=,kmalloc-4096' for consistent
behavior with older kernels.
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