[PATCH] taskstats_exit_alloc: optimize/simplify

If there are no listeners, every task does unneeded kmem_cache alloc/free on
exit. We don't need listeners->sem for 'if (!list_empty())' check. Yes, we may
have a false positive, but this doesn't differ from the case when the listener
is unregistered after we drop the semaphore. So we don't need to do allocation
beforehand.

Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>
Cc: Balbir Singh <balbir@in.ibm.com>
Acked-by: Shailabh Nagar <nagar@watson.ibm.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

diff --git a/kernel/taskstats.c b/kernel/taskstats.c
index f5f9201..d9d7c35 100644 (file)
--- a/kernel/taskstats.c
+++ b/kernel/taskstats.c
@@ -416,7 +416,6 @@ err:
 void taskstats_exit_alloc(struct taskstats **ptidstats, unsigned int *mycpu)
 {
        struct listener_list *listeners;
-       struct taskstats *tmp;
        /*
         * This is the cpu on which the task is exiting currently and will
         * be the one for which the exit event is sent, even if the cpu
@@ -424,19 +423,11 @@ void taskstats_exit_alloc(struct taskstats **ptidstats, unsigned int *mycpu)
         */
        *mycpu = raw_smp_processor_id();
 
-       *ptidstats = NULL;
-       tmp = kmem_cache_zalloc(taskstats_cache, GFP_KERNEL);
-       if (!tmp)
-               return;
-
        listeners = &per_cpu(listener_array, *mycpu);
-       down_read(&listeners->sem);
-       if (!list_empty(&listeners->list)) {
-               *ptidstats = tmp;
-               tmp = NULL;
-       }
-       up_read(&listeners->sem);
-       kfree(tmp);
+
+       *ptidstats = NULL;
+       if (!list_empty(&listeners->list))
+               *ptidstats = kmem_cache_zalloc(taskstats_cache, GFP_KERNEL);
 }
 
 /* Send pid data out on exit */