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Commit 128fb956 authored by Oleg Nesterov's avatar Oleg Nesterov Committed by Linus Torvalds
Browse files

[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: default avatarOleg Nesterov <oleg@tv-sign.ru>
Cc: Balbir Singh <balbir@in.ibm.com>
Acked-by: default avatarShailabh Nagar <nagar@watson.ibm.com>
Signed-off-by: default avatarAndrew Morton <akpm@osdl.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>
parent 38da288b

kernel/taskstats.c

+4 −13
Original line number Diff line number Diff line
@@ -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 */