[PATCH] taskstats_exit_alloc: optimize/simplify (128fb956) · Commits · 戴 / test

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>

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 */

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