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

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Date:   Mon, 31 Jul 2017 11:56:24 -0700
From:   Mike Kravetz <mike.kravetz@...cle.com>
To:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        linux-arch@...r.kernel.org
Cc:     Matthew Wilcox <willy@...radead.org>,
        Michal Hocko <mhocko@...nel.org>, akpm@...ux-foundation.org,
        ak@...ux.intel.com, mtk.manpages@...il.com,
        Davidlohr Bueso <dbueso@...e.de>, khandual@...ux.vnet.ibm.com,
        aneesh.kumar@...ux.vnet.ibm.com, aarcange@...hat.com,
        Arnd Bergmann <arnd@...db.de>,
        Mike Kravetz <mike.kravetz@...cle.com>
Subject: [PATCH 1/3] mm:hugetlb: Define system call hugetlb size encodings in single file

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.  The primary uapi
header files for mmap and shm will use these definitions as a basis
for definitions specific to those system calls.

Signed-off-by: Mike Kravetz <mike.kravetz@...cle.com>
---
 include/uapi/asm-generic/hugetlb_encode.h | 34 +++++++++++++++++++++++++++++++
 1 file changed, 34 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..e4732d3
--- /dev/null
+++ b/include/uapi/asm-generic/hugetlb_encode.h
@@ -0,0 +1,34 @@
+#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_64KB	(16 << HUGETLB_FLAG_ENCODE_SHIFT)
+#define HUGETLB_FLAG_ENCODE_512KB	(19 << HUGETLB_FLAG_ENCODE_SHIFT)
+#define HUGETLB_FLAG_ENCODE_1MB		(20 << HUGETLB_FLAG_ENCODE_SHIFT)
+#define HUGETLB_FLAG_ENCODE_2MB		(21 << HUGETLB_FLAG_ENCODE_SHIFT)
+#define HUGETLB_FLAG_ENCODE_8MB		(23 << HUGETLB_FLAG_ENCODE_SHIFT)
+#define HUGETLB_FLAG_ENCODE_16MB	(24 << HUGETLB_FLAG_ENCODE_SHIFT)
+#define HUGETLB_FLAG_ENCODE_256MB	(28 << HUGETLB_FLAG_ENCODE_SHIFT)
+#define HUGETLB_FLAG_ENCODE_1GB		(30 << HUGETLB_FLAG_ENCODE_SHIFT)
+#define HUGETLB_FLAG_ENCODE_2GB		(31 << HUGETLB_FLAG_ENCODE_SHIFT)
+#define HUGETLB_FLAG_ENCODE_16GB	(34 << HUGETLB_FLAG_ENCODE_SHIFT)
+
+#endif /* _ASM_GENERIC_HUGETLB_ENCODE_H_ */
-- 
2.7.5