[RFC PATCH 1/3] mm:hugetlb: Define system call hugetlb size encodings in single file

[Mike Kravetz]

If hugetlb pages are requested in mmap or shmget system calls,  a huge
page size other than default can be requested.  This is accomplished by
encoding the log2 of the huge page size in the upper bits of the flag
argument.  asm-generic and arch specific headers all define the same
values for these encodings.

Put common definitions in a single header file.  arch specific code can
still override if desired.

Signed-off-by: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
---
 include/uapi/asm-generic/hugetlb_encode.h | 30 ++++++++++++++++++++++++++++++
 1 file changed, 30 insertions(+)
 create mode 100644 include/uapi/asm-generic/hugetlb_encode.h

diff --git a/include/uapi/asm-generic/hugetlb_encode.h b/include/uapi/asm-generic/hugetlb_encode.h
new file mode 100644
index 0000000..aa09fc0
--- /dev/null
+++ b/include/uapi/asm-generic/hugetlb_encode.h
@@ -0,0 +1,30 @@
+#ifndef _ASM_GENERIC_HUGETLB_ENCODE_H_
+#define _ASM_GENERIC_HUGETLB_ENCODE_H_
+
+/*
+ * Several system calls take a flag to request "hugetlb" huge pages.
+ * Without further specification, these system calls will use the
+ * system's default huge page size.  If a system supports multiple
+ * huge page sizes, the desired huge page size can be specified in
+ * bits [26:31] of the flag arguments.  The value in these 6 bits
+ * will encode the log2 of the huge page size.
+ *
+ * The following definitions are associated with this huge page size
+ * encoding in flag arguments.  System call specific header files
+ * that use this encoding should include this file.  They can then
+ * provide definitions based on these with their own specific prefix.
+ * for example #define MAP_HUGE_SHIFT HUGETLB_FLAG_ENCODE_SHIFT.
+ */
+
+#define HUGETLB_FLAG_ENCODE_SHIFT	26
+#define HUGETLB_FLAG_ENCODE_MASK	0x3f
+
+#define HUGETLB_FLAG_ENCODE_512KB	(19 << MAP_HUGE_SHIFT
+#define HUGETLB_FLAG_ENCODE_1MB		(20 << MAP_HUGE_SHIFT)
+#define HUGETLB_FLAG_ENCODE_2MB		(21 << MAP_HUGE_SHIFT)
+#define HUGETLB_FLAG_ENCODE_8MB		(23 << MAP_HUGE_SHIFT)
+#define HUGETLB_FLAG_ENCODE_16MB	(24 << MAP_HUGE_SHIFT)
+#define HUGETLB_FLAG_ENCODE_1GB		(30 << MAP_HUGE_SHIFT)
+#define HUGETLB_FLAG_ENCODE__16GB	(34 << MAP_HUGE_SHIFT)
+
+#endif /* _ASM_GENERIC_HUGETLB_ENCODE_H_ */
-- 
2.7.5