Message-ID: <48B4542A.1050004@sgi.com>
Date: Tue, 26 Aug 2008 12:06:18 -0700
From: Mike Travis <travis@sgi.com>
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To: David Miller <davem@davemloft.net>
CC: mingo@elte.hu, torvalds@linux-foundation.org, Alan.Brunelle@hp.com,
       tglx@linutronix.de, rjw@sisk.pl, linux-kernel@vger.kernel.org,
       kernel-testers@vger.kernel.org, akpm@linux-foundation.org,
       arjan@linux.intel.com, rusty@rustcorp.com.au
Subject: Re: [Bug #11342] Linux 2.6.27-rc3: kernel BUG at mm/vmalloc.c - bisected
References: <alpine.LFD.1.10.0808251344250.3363@nehalem.linux-foundation.org>	<alpine.LFD.1.10.0808251401590.3363@nehalem.linux-foundation.org>	<20080826072220.GB31876@elte.hu> <20080826.004607.253712060.davem@davemloft.net>
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David Miller wrote:
> From: Ingo Molnar <mingo@elte.hu>
> Date: Tue, 26 Aug 2008 09:22:20 +0200
> 
>> And i guess the next generation of 4K CPUs support should just get away 
>> from cpumask_t-on-kernel-stack model altogether, as the current model is 
>> not maintainable. We tried the on-kernel-stack variant, and it really 
>> does not work reliably. We can fix this in v2.6.28.
> 
> I recently did some work on sparc64 to use cpumask pointers
> as much as possible.
> 
> The only case that didn't work was due to a limitation in
> arch interfaces for the new generic smp_call_function() code.
> It passes a cpumask_t instead of a pointer to one via
> arch_send_call_function_ipi().
> 
> But other than that, the whole sparc64 SMP stuff uses cpumask_t
> pointers only.
> 
> What it comes down to is that you have to do the "self cpu"
> and other tests in the cross-call dispatch routines themselves,
> instead of at the top-level working on cpumask_t objects.
> 
> Otherwise you have to modify cpumask_t objects and thus pluck
> them onto the stack where they take up silly amounts of space.

Yes, I had proposed either modifying, or supplementing a new
smp_call function to pass the cpumask_t as a pointer (similar
to set_cpus_allowed_ptr.)  But an ABI change such as this was
not well received at the time.

Thanks,
Mike
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