selftests/mm: fix build failures due to missing MADV_COLLAPSE

MADV_PAGEOUT, MADV_POPULATE_READ, MADV_COLLAPSE are conditionally
defined as necessary. However, that was being done in .c files, and a
new build failure came up that would have been automatically avoided had
these been in a common header file.

So consolidate and move them all to vm_util.h, which fixes the build
failure.

An alternative approach from Muhammad Usama Anjum was: rely on "make
headers" being required, and include asm-generic/mman-common.h. This
works in the sense that it builds, but it still generates warnings about
duplicate MADV_* symbols, and the goal here is to get a fully clean (no
warnings) build here.

Link: https://lkml.kernel.org/r/20230606071637.267103-9-jhubbard@nvidia.com
Signed-off-by: John Hubbard <jhubbard@nvidia.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Tested-by: Muhammad Usama Anjum <usama.anjum@collabora.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Nathan Chancellor <nathan@kernel.org>
Cc: Shuah Khan <shuah@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

tools/testing/selftests/mm/cow.c

@@ -29,13 +29,6 @@
 #include "../kselftest.h"
 #include "vm_util.h"
 
-#ifndef MADV_PAGEOUT
-#define MADV_PAGEOUT 21
-#endif
-#ifndef MADV_COLLAPSE
-#define MADV_COLLAPSE 25
-#endif
-
 static size_t pagesize;
 static int pagemap_fd;
 static size_t thpsize;

tools/testing/selftests/mm/khugepaged.c

@@ -22,16 +22,6 @@
 
 #include "vm_util.h"
 
-#ifndef MADV_PAGEOUT
-#define MADV_PAGEOUT 21
-#endif
-#ifndef MADV_POPULATE_READ
-#define MADV_POPULATE_READ 22
-#endif
-#ifndef MADV_COLLAPSE
-#define MADV_COLLAPSE 25
-#endif
-
 #define BASE_ADDR ((void *)(1UL << 30))
 static unsigned long hpage_pmd_size;
 static unsigned long page_size;

tools/testing/selftests/mm/vm_util.h

@@ -64,3 +64,13 @@ int uffd_register_with_ioctls(int uffd, void *addr, uint64_t len,
 
 #define PAGEMAP_PRESENT(ent)	(((ent) & (1ull << 63)) != 0)
 #define PAGEMAP_PFN(ent)	((ent) & ((1ull << 55) - 1))
+
+#ifndef MADV_PAGEOUT
+#define MADV_PAGEOUT 21
+#endif
+#ifndef MADV_POPULATE_READ
+#define MADV_POPULATE_READ 22
+#endif
+#ifndef MADV_COLLAPSE
+#define MADV_COLLAPSE 25
+#endif