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Date: Fri, 19 Dec 2008 20:41:49 -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: > Steven Rostedt wrote: > > On Fri, 19 Dec 2008, Mike Travis wrote: > > > >> Impact: Reduce memory usage, use new cpumask API. > >> > >> Convert kernel trace functions to use struct cpumask. > >> > > 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. For future memory savings... Acked-by: Steven Rostedt <srostedt@...hat.com> -- Steve -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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