1 files changed, 15 insertions, 0 deletions

diff --git a/include/linux/shm.h b/include/linux/shm.h
index bcf8a6a3ec00..429c1995d756 100644
--- a/include/linux/shm.h
+++ b/include/linux/shm.h
@@ -29,6 +29,21 @@ struct shmid_kernel /* private to the kernel */
 #define SHM_HUGETLB     04000   /* segment will use huge TLB pages */
 #define SHM_NORESERVE   010000  /* don't check for reservations */
 
+/* Bits [26:31] are reserved */
+
+/*
+ * When SHM_HUGETLB is set bits [26:31] encode the log2 of the huge page size.
+ * This gives us 6 bits, which is enough until someone invents 128 bit address
+ * spaces.
+ *
+ * Assume these are all power of twos.
+ * When 0 use the default page size.
+ */
+#define SHM_HUGE_SHIFT  26
+#define SHM_HUGE_MASK   0x3f
+#define SHM_HUGE_2MB    (21 << SHM_HUGE_SHIFT)
+#define SHM_HUGE_1GB    (30 << SHM_HUGE_SHIFT)
+
 #ifdef CONFIG_SYSVIPC
 long do_shmat(int shmid, char __user *shmaddr, int shmflg, unsigned long *addr,
               unsigned long shmlba);