mm, hugepages: make memory size variable in hugepage-mremap selftest

The hugetlb vma mremap() test currently maps 1GB of memory to trigger
pmd sharing and make sure that 'unshare' path in mremap code works. The
test originally only mapped 10MB of memory (as specified by the header
comment) but was later modified to 1GB to tackle this case.

However, not all machines will have 1GB of memory to spare for this
test. Adding a mapping size arg will allow run_vmtest.sh to pass an
adequate mapping size, while allowing users to run the test
independently with arbitrary size mappings.

Link: https://lkml.kernel.org/r/[e-mail]
Signed-off-by: Yosry Ahmed <[e-mail]>
Cc: Shuah Khan <[e-mail]>
Cc: Mina Almasry <[e-mail]>
Cc: Mike Kravetz <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

tools/testing/selftests/vm/hugepage-mremap.c

···
  *
  * Example of remapping huge page memory in a user application using the
  * mremap system call.  Code assumes a hugetlbfs filesystem is mounted
- * at './huge'.  The code will use 10MB worth of huge pages.
+ * at './huge'.  The amount of memory used by this test is decided by a command
+ * line argument in MBs. If missing, the default amount is 10MB.
+ *
+ * To make sure the test triggers pmd sharing and goes through the 'unshare'
+ * path in the mremap code use 1GB (1024) or more.
  */
 
 #define _GNU_SOURCE
···
 #include <linux/userfaultfd.h>
 #include <sys/ioctl.h>
 
-#define LENGTH (1UL * 1024 * 1024 * 1024)
+#define DEFAULT_LENGTH_MB 10UL
+#define MB_TO_BYTES(x) (x * 1024 * 1024)
 
+#define FILE_NAME "huge/hugepagefile"
 #define PROTECTION (PROT_READ | PROT_WRITE | PROT_EXEC)
 #define FLAGS (MAP_SHARED | MAP_ANONYMOUS)
 
···
 	printf("First hex is %x\n", *((unsigned int *)addr));
 }
 
-static void write_bytes(char *addr)
+static void write_bytes(char *addr, size_t len)
 {
 	unsigned long i;
 
-	for (i = 0; i < LENGTH; i++)
+	for (i = 0; i < len; i++)
 		*(addr + i) = (char)i;
 }
 
-static int read_bytes(char *addr)
+static int read_bytes(char *addr, size_t len)
 {
 	unsigned long i;
 
 	check_bytes(addr);
-	for (i = 0; i < LENGTH; i++)
+	for (i = 0; i < len; i++)
 		if (*(addr + i) != (char)i) {
 			printf("Mismatch at %lu\n", i);
 			return 1;
···
 	}
 }
 
-int main(void)
+int main(int argc, char *argv[])
 {
+	/* Read memory length as the first arg if valid, otherwise fallback to
+	 * the default length. Any additional args are ignored.
+	 */
+	size_t length = argc > 1 ? (size_t)atoi(argv[1]) : 0UL;
+
+	length = length > 0 ? length : DEFAULT_LENGTH_MB;
+	length = MB_TO_BYTES(length);
+
 	int ret = 0;
 
-	int fd = open("/huge/test", O_CREAT | O_RDWR, 0755);
+	int fd = open(FILE_NAME, O_CREAT | O_RDWR, 0755);
 
 	if (fd < 0) {
 		perror("Open failed");
···
 
 	/* mmap to a PUD aligned address to hopefully trigger pmd sharing. */
 	unsigned long suggested_addr = 0x7eaa40000000;
-	void *haddr = mmap((void *)suggested_addr, LENGTH, PROTECTION,
+	void *haddr = mmap((void *)suggested_addr, length, PROTECTION,
 			   MAP_HUGETLB | MAP_SHARED | MAP_POPULATE, fd, 0);
 	printf("Map haddr: Returned address is %p\n", haddr);
 	if (haddr == MAP_FAILED) {
···
 
 	/* mmap again to a dummy address to hopefully trigger pmd sharing. */
 	suggested_addr = 0x7daa40000000;
-	void *daddr = mmap((void *)suggested_addr, LENGTH, PROTECTION,
+	void *daddr = mmap((void *)suggested_addr, length, PROTECTION,
 			   MAP_HUGETLB | MAP_SHARED | MAP_POPULATE, fd, 0);
 	printf("Map daddr: Returned address is %p\n", daddr);
 	if (daddr == MAP_FAILED) {
···
 
 	suggested_addr = 0x7faa40000000;
 	void *vaddr =
-		mmap((void *)suggested_addr, LENGTH, PROTECTION, FLAGS, -1, 0);
+		mmap((void *)suggested_addr, length, PROTECTION, FLAGS, -1, 0);
 	printf("Map vaddr: Returned address is %p\n", vaddr);
 	if (vaddr == MAP_FAILED) {
 		perror("mmap2");
 		exit(1);
 	}
 
-	register_region_with_uffd(haddr, LENGTH);
+	register_region_with_uffd(haddr, length);
 
-	void *addr = mremap(haddr, LENGTH, LENGTH,
+	void *addr = mremap(haddr, length, length,
 			    MREMAP_MAYMOVE | MREMAP_FIXED, vaddr);
 	if (addr == MAP_FAILED) {
 		perror("mremap");
···
 
 	printf("Mremap: Returned address is %p\n", addr);
 	check_bytes(addr);
-	write_bytes(addr);
-	ret = read_bytes(addr);
+	write_bytes(addr, length);
+	ret = read_bytes(addr, length);
 
-	munmap(addr, LENGTH);
+	munmap(addr, length);
 
 	return ret;
 }

tools/testing/selftests/vm/run_vmtests.sh

···
 echo "-----------------------"
 echo "running hugepage-mremap"
 echo "-----------------------"
-./hugepage-mremap
+./hugepage-mremap 256
 if [ $? -ne 0 ]; then
 	echo "[FAIL]"
 	exitcode=1