SHMEM_TRUNCATE    544 mm/shmem.c     	info->flags |= SHMEM_TRUNCATE;
SHMEM_TRUNCATE    726 mm/shmem.c     	info->flags &= ~SHMEM_TRUNCATE;
SHMEM_TRUNCATE   1032 mm/shmem.c     		BUG_ON(!(info->flags & SHMEM_TRUNCATE));