dm ioctl: use kmalloc if possible

If the parameter buffer is small enough, try to allocate it with kmalloc()
rather than vmalloc().

vmalloc is noticeably slower than kmalloc because it has to manipulate
page tables.

In my tests, on PA-RISC this patch speeds up activation 13 times.
On Opteron this patch speeds up activation by 5%.

This patch introduces a new function free_params() to free the
parameters and this uses new flags that record whether or not vmalloc()
was used and whether or not the input buffer must be wiped after use.
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>

drivers/md/dm-ioctl.c

@@ -1543,7 +1543,21 @@ static int check_version(unsigned int cmd, struct dm_ioctl __user *user)
 	return r;
 }
 
-static int copy_params(struct dm_ioctl __user *user, struct dm_ioctl **param)
+#define DM_PARAMS_VMALLOC	0x0001	/* Params alloced with vmalloc not kmalloc */
+#define DM_WIPE_BUFFER		0x0010	/* Wipe input buffer before returning from ioctl */
+
+static void free_params(struct dm_ioctl *param, size_t param_size, int param_flags)
+{
+	if (param_flags & DM_WIPE_BUFFER)
+		memset(param, 0, param_size);
+
+	if (param_flags & DM_PARAMS_VMALLOC)
+		vfree(param);
+	else
+		kfree(param);
+}
+
+static int copy_params(struct dm_ioctl __user *user, struct dm_ioctl **param, int *param_flags)
 {
 	struct dm_ioctl tmp, *dmi;
 	int secure_data;
@@ -1556,10 +1570,21 @@ static int copy_params(struct dm_ioctl __user *user, struct dm_ioctl **param)
 
 	secure_data = tmp.flags & DM_SECURE_DATA_FLAG;
 
+	*param_flags = secure_data ? DM_WIPE_BUFFER : 0;
+
 	/*
 	 * Try to avoid low memory issues when a device is suspended.
+	 * Use kmalloc() rather than vmalloc() when we can.
 	 */
+	dmi = NULL;
+	if (tmp.data_size <= KMALLOC_MAX_SIZE)
+		dmi = kmalloc(tmp.data_size, GFP_NOIO | __GFP_NORETRY | __GFP_NOMEMALLOC | __GFP_NOWARN);
+
+	if (!dmi) {
 		dmi = __vmalloc(tmp.data_size, GFP_NOIO | __GFP_REPEAT | __GFP_HIGH, PAGE_KERNEL);
+		*param_flags |= DM_PARAMS_VMALLOC;
+	}
+
 	if (!dmi) {
 		if (secure_data && clear_user(user, tmp.data_size))
 			return -EFAULT;
@@ -1585,9 +1610,8 @@ static int copy_params(struct dm_ioctl __user *user, struct dm_ioctl **param)
 	return 0;
 
 bad:
-	if (secure_data)
-		memset(dmi, 0, tmp.data_size);
-	vfree(dmi);
+	free_params(dmi, tmp.data_size, *param_flags);
+
 	return -EFAULT;
 }
 
@@ -1624,7 +1648,7 @@ static int validate_params(uint cmd, struct dm_ioctl *param)
 static int ctl_ioctl(uint command, struct dm_ioctl __user *user)
 {
 	int r = 0;
-	int wipe_buffer;
+	int param_flags;
 	unsigned int cmd;
 	struct dm_ioctl *uninitialized_var(param);
 	ioctl_fn fn = NULL;
@@ -1662,14 +1686,12 @@ static int ctl_ioctl(uint command, struct dm_ioctl __user *user)
 	/*
 	 * Copy the parameters into kernel space.
 	 */
-	r = copy_params(user, &param);
+	r = copy_params(user, &param, &param_flags);
 
 	if (r)
 		return r;
 
 	input_param_size = param->data_size;
-	wipe_buffer = param->flags & DM_SECURE_DATA_FLAG;
-
 	r = validate_params(cmd, param);
 	if (r)
 		goto out;
@@ -1684,10 +1706,7 @@ static int ctl_ioctl(uint command, struct dm_ioctl __user *user)
 		r = -EFAULT;
 
 out:
-	if (wipe_buffer)
-		memset(param, 0, input_param_size);
-
-	vfree(param);
+	free_params(param, input_param_size, param_flags);
 	return r;
 }