Commit 03a285f5 authored Jan 08, 2006 by Paul Jackson Committed by Linus Torvalds Jan 08, 2006

[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>

parent 7edc5962

kernel/cpuset.c

+9 −4

Original line number	Diff line number	Diff line
		@@ -647,10 +647,15 @@ void cpuset_update_task_memory_state()
		struct task_struct *tsk = current;
		struct cpuset *cs;

		if (tsk->cpuset == &top_cpuset) {
		/* Don't need rcu for top_cpuset. It's never freed. */
		my_cpusets_mem_gen = top_cpuset.mems_generation;
		} else {
		rcu_read_lock();
		cs = rcu_dereference(tsk->cpuset);
		my_cpusets_mem_gen = cs->mems_generation;
		rcu_read_unlock();
		}

		if (my_cpusets_mem_gen != tsk->cpuset_mems_generation) {
		down(&callback_sem);