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[PATCH] cpuset: skip rcu check if task is in root cpuset
For systems that aren't using cpusets, but have them CONFIG_CPUSET enabled in their kernel (eventually this may be most distribution kernels), this patch removes even the minimal rcu_read_lock() from the memory page allocation path. Actually, it removes that rcu call for any task that is in the root cpuset (top_cpuset), which on systems not actively using cpusets, is all tasks. We don't need the rcu check for tasks in the top_cpuset, because the top_cpuset is statically allocated, so at no risk of being freed out from underneath us. Signed-off-by: Paul Jackson <pj@sgi.com> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
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@ -647,10 +647,15 @@ void cpuset_update_task_memory_state()
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struct task_struct *tsk = current;
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struct cpuset *cs;
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if (tsk->cpuset == &top_cpuset) {
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/* Don't need rcu for top_cpuset. It's never freed. */
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my_cpusets_mem_gen = top_cpuset.mems_generation;
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} else {
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rcu_read_lock();
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cs = rcu_dereference(tsk->cpuset);
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my_cpusets_mem_gen = cs->mems_generation;
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rcu_read_unlock();
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}
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if (my_cpusets_mem_gen != tsk->cpuset_mems_generation) {
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down(&callback_sem);
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