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 <[email protected]>
---
kernel/cpuset.c | 13 +++++++++----
1 files changed, 9 insertions(+), 4 deletions(-)
--- 2.6.15-rc3-mm1.orig/kernel/cpuset.c 2005-12-13 18:14:42.529952708 -0800
+++ 2.6.15-rc3-mm1/kernel/cpuset.c 2005-12-13 20:54:26.323911532 -0800
@@ -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);
--
I won't rest till it's the best ...
Programmer, Linux Scalability
Paul Jackson <[email protected]> 1.650.933.1373
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