mm: add comment about deprecation of __GFP_NOFAIL

__GFP_NOFAIL was deprecated in dab48dab, so add a comment that no new
users should be added.

Reviewed-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Signed-off-by: David Rientjes <rientjes@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

include/linux/gfp.h

@@ -30,7 +30,8 @@ struct vm_area_struct;
  * _might_ fail.  This depends upon the particular VM implementation.
  *
  * __GFP_NOFAIL: The VM implementation _must_ retry infinitely: the caller
- * cannot handle allocation failures.
+ * cannot handle allocation failures.  This modifier is deprecated and no new
+ * users should be added.
  *
  * __GFP_NORETRY: The VM implementation must not retry indefinitely.
  *