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Subject[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>

--- STATS/kernel/taskstats.c~1_alloc 2006-10-29 18:35:40.000000000 +0300
+++ STATS/kernel/taskstats.c 2006-10-30 23:45:20.000000000 +0300
@@ -421,7 +421,6 @@ 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
@@ -429,19 +428,11 @@ void taskstats_exit_alloc(struct tasksta
*/
*mycpu = raw_smp_processor_id();

- *ptidstats = NULL;
- tmp = kmem_cache_zalloc(taskstats_cache, SLAB_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, SLAB_KERNEL);
}

/* Send pid data out on exit */
-
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