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Message-ID: <alpine.DEB.1.10.0812191201200.26432@gandalf.stny.rr.com>
Date: Fri, 19 Dec 2008 12:01:51 -0500 (EST)
From: Steven Rostedt <rostedt@...dmis.org>
To: Mike Travis <travis@....com>
cc: Ingo Molnar <mingo@...hat.com>,
Rusty Russell <rusty@...tcorp.com.au>,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH 4/8] cpumask: convert kernel trace functions
On Fri, 19 Dec 2008, Mike Travis wrote:
> >
> >
> > How does this save memory if we just allocate a cpumask var everytime
> > we allocate a ring buffer? Is cpumask_var_t a mask of possible CPUS and
> > not NR_CPUS?
> >
> > Otherwise, I see this as just adding one extra pointer.
> >
> > -- Steve
>
> Hi Steve,
>
> Yes, eventually, the cpumask_var_t will be allocated based on cpumask_size()
> which will become BITS_TO_LONG(nr_cpu_ids) instead of BITS_TO_LONGS(NR_CPUS)
> as soon as the kernel becomes "cpumask" clean. (clean being that it ignores
> all bits >= nr_cpu_ids.)
>
> Note that on small NR_CPUS count systems, cpumask_var_t is a static array
> and no allocation happens, so it only kicks in when CONFIG_CPUMASK_OFFSTACK=y.
OK, that explains a lot. Thanks for the explanation.
-- Steve
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