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[PATCH] cpuset: skip rcu check if task is in root cpuset

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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>
This commit is contained in:
Paul Jackson 2006-01-08 01:02:04 -08:00 committed by Linus Torvalds
parent 7edc59628b
commit 03a285f580
1 changed files with 9 additions and 4 deletions
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13
kernel/cpuset.c
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@ -647,10 +647,15 @@ void cpuset_update_task_memory_state()
struct task_struct *tsk = current;
struct cpuset *cs;
rcu_read_lock();
cs = rcu_dereference(tsk->cpuset);
my_cpusets_mem_gen = cs->mems_generation;
rcu_read_unlock();
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);