[PATCH] taskstats_tgid_alloc: optimization

Every subthread (except first) does unneeded kmem_cache_alloc/kmem_cache_free.
Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>
Cc: Shailabh Nagar <nagar@watson.ibm.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Jay Lan <jlan@sgi.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

include/linux/taskstats_kern.h

@@ -32,6 +32,9 @@ static inline void taskstats_tgid_alloc(struct signal_struct *sig)
 	struct taskstats *stats;
 	unsigned long flags;
 
+	if (sig->stats != NULL)
+		return;
+
 	stats = kmem_cache_zalloc(taskstats_cache, SLAB_KERNEL);
 	if (!stats)
 		return;