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SubjectRe: [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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