aboutsummaryrefslogtreecommitdiffstatshomepage
path: root/tools/testing/selftests/mm/hugepage-shm.c
diff options
context:
space:
mode:
Diffstat (limited to 'tools/testing/selftests/mm/hugepage-shm.c')
-rw-r--r--tools/testing/selftests/mm/hugepage-shm.c81
1 files changed, 81 insertions, 0 deletions
diff --git a/tools/testing/selftests/mm/hugepage-shm.c b/tools/testing/selftests/mm/hugepage-shm.c
new file mode 100644
index 000000000000..ef06260802b5
--- /dev/null
+++ b/tools/testing/selftests/mm/hugepage-shm.c
@@ -0,0 +1,81 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * hugepage-shm:
+ *
+ * Example of using huge page memory in a user application using Sys V shared
+ * memory system calls. In this example the app is requesting 256MB of
+ * memory that is backed by huge pages. The application uses the flag
+ * SHM_HUGETLB in the shmget system call to inform the kernel that it is
+ * requesting huge pages.
+ *
+ * Note: The default shared memory limit is quite low on many kernels,
+ * you may need to increase it via:
+ *
+ * echo 268435456 > /proc/sys/kernel/shmmax
+ *
+ * This will increase the maximum size per shared memory segment to 256MB.
+ * The other limit that you will hit eventually is shmall which is the
+ * total amount of shared memory in pages. To set it to 16GB on a system
+ * with a 4kB pagesize do:
+ *
+ * echo 4194304 > /proc/sys/kernel/shmall
+ */
+
+#include <stdlib.h>
+#include <stdio.h>
+#include <sys/types.h>
+#include <sys/ipc.h>
+#include <sys/shm.h>
+#include <sys/mman.h>
+
+#define LENGTH (256UL*1024*1024)
+
+#define dprintf(x) printf(x)
+
+int main(void)
+{
+ int shmid;
+ unsigned long i;
+ char *shmaddr;
+
+ shmid = shmget(2, LENGTH, SHM_HUGETLB | IPC_CREAT | SHM_R | SHM_W);
+ if (shmid < 0) {
+ perror("shmget");
+ exit(1);
+ }
+ printf("shmid: 0x%x\n", shmid);
+
+ shmaddr = shmat(shmid, NULL, 0);
+ if (shmaddr == (char *)-1) {
+ perror("Shared memory attach failure");
+ shmctl(shmid, IPC_RMID, NULL);
+ exit(2);
+ }
+ printf("shmaddr: %p\n", shmaddr);
+
+ dprintf("Starting the writes:\n");
+ for (i = 0; i < LENGTH; i++) {
+ shmaddr[i] = (char)(i);
+ if (!(i % (1024 * 1024)))
+ dprintf(".");
+ }
+ dprintf("\n");
+
+ dprintf("Starting the Check...");
+ for (i = 0; i < LENGTH; i++)
+ if (shmaddr[i] != (char)i) {
+ printf("\nIndex %lu mismatched\n", i);
+ exit(3);
+ }
+ dprintf("Done.\n");
+
+ if (shmdt((const void *)shmaddr) != 0) {
+ perror("Detach failure");
+ shmctl(shmid, IPC_RMID, NULL);
+ exit(4);
+ }
+
+ shmctl(shmid, IPC_RMID, NULL);
+
+ return 0;
+}