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| author | Paul Jackson <pj@sgi.com> | 2006-01-08 01:02:04 -0800 |
|---|---|---|
| committer | Linus Torvalds <torvalds@g5.osdl.org> | 2006-01-08 20:13:45 -0800 |
| commit | 03a285f58064b8e0af08383e082e383753d9c33e (patch) | |
| tree | af458f3357d4e2d01dc04d2d41a7dd7d502c4755 | |
| parent | 7edc59628b2f5d6516b4677b3b56f5f056e45cd9 (diff) | |
| download | lwn-03a285f58064b8e0af08383e082e383753d9c33e.tar.gz lwn-03a285f58064b8e0af08383e082e383753d9c33e.zip | |
[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>
| -rw-r--r-- | kernel/cpuset.c | 13 |
1 files changed, 9 insertions, 4 deletions
diff --git a/kernel/cpuset.c b/kernel/cpuset.c index 681a5d58d40d..e04c2da9dadb 100644 --- a/kernel/cpuset.c +++ b/kernel/cpuset.c @@ -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); |