[PATCH 01/16] mm: Add MAP_BELOW_HINT

Charlie Jenkins
2024-08-28T05:49:29Z

Some applications rely on placing data in free bits addresses allocated
by mmap. Various architectures (eg. x86, arm64, powerpc) restrict the
address returned by mmap to be less than the maximum address space,
unless the hint address is greater than this value.

To make this behavior explicit and more versatile across all
architectures, define a mmap flag that allows users to define an
arbitrary upper limit on addresses returned by mmap.

Signed-off-by: Charlie Jenkins <charlie@rivosinc.com>
---
include/uapi/asm-generic/mman-common.h | 1 +
tools/include/uapi/asm-generic/mman-common.h | 1 +
2 files changed, 2 insertions(+)

diff --git a/include/uapi/asm-generic/mman-common.h b/include/uapi/asm-generic/mman-common.h
index 6ce1f1ceb432..03ac13d9aa37 100644
--- a/include/uapi/asm-generic/mman-common.h
+++ b/include/uapi/asm-generic/mman-common.h
@@ -32,6 +32,7 @@

#define MAP_UNINITIALIZED 0x4000000 /* For anonymous mmap, memory could be
* uninitialized */
+#define MAP_BELOW_HINT 0x8000000 /* give out address that is below (inclusive) hint address */

/*
* Flags for mlock
diff --git a/tools/include/uapi/asm-generic/mman-common.h b/tools/include/uapi/asm-generic/mman-common.h
index 6ce1f1ceb432..03ac13d9aa37 100644
--- a/tools/include/uapi/asm-generic/mman-common.h
+++ b/tools/include/uapi/asm-generic/mman-common.h
@@ -32,6 +32,7 @@

#define MAP_UNINITIALIZED 0x4000000 /* For anonymous mmap, memory could be
* uninitialized */
+#define MAP_BELOW_HINT 0x8000000 /* give out address that is below (inclusive) hint address */

/*
* Flags for mlock

--
2.45.0