btrfs: move read policies out of experimental

Read policies seem safe and stable enough to move it out of the
experimental feature set. This allows us to add more policies without
forcing users to enable the full experimental feature set.

Signed-off-by: Kai Krakow <kai@kaishome.de>

Author: kakra

fs/btrfs/Kconfig

@@ -141,6 +141,21 @@ config BTRFS_PER_DEVICE_IO_STATS
 
 	  If unsure, say N.
 
+config BTRFS_READ_POLICIES
+	bool "Btrfs read policies"
+	depends on BTRFS_FS
+	default n
+	help
+	  This enables btrfs read policies to control how btrfs selects stripes
+	  from a mirror during read operations. This was originally part of
+	  the experimental feature set but it is safe to use and can provide
+	  huge performance benefits in certain scenarios without causing any
+	  performance regressions.
+
+	  This adds a new file /sys/fs/btrfs/BTRFS-UUID/read_policy.
+
+	  If unsure, say N.
+
 config BTRFS_EXPERIMENTAL
 	bool "Btrfs experimental features"
 	depends on BTRFS_FS

fs/btrfs/super.c

@@ -2498,7 +2498,7 @@ static int __init btrfs_print_mod_info(void)
 #endif
 			;
 
-#ifdef CONFIG_BTRFS_EXPERIMENTAL
+#ifdef CONFIG_BTRFS_READ_POLICIES
 	if (btrfs_get_mod_read_policy() == NULL)
 		pr_info("Btrfs loaded%s\n", options);
 	else
@@ -2565,7 +2565,7 @@ static const struct init_sequence mod_init_seq[] = {
 	}, {
 		.init_func = btrfs_extent_map_init,
 		.exit_func = btrfs_extent_map_exit,
-#ifdef CONFIG_BTRFS_EXPERIMENTAL
+#ifdef CONFIG_BTRFS_READ_POLICIES
 	}, {
 		.init_func = btrfs_read_policy_init,
 		.exit_func = NULL,

fs/btrfs/sysfs.c

@@ -1323,13 +1323,13 @@ BTRFS_ATTR(, temp_fsid, btrfs_temp_fsid_show);
 
 static const char *btrfs_read_policy_name[] = {
 	"pid",
-#ifdef CONFIG_BTRFS_EXPERIMENTAL
+#ifdef CONFIG_BTRFS_READ_POLICIES
 	"round-robin",
 	"devid",
 #endif
 };
 
-#ifdef CONFIG_BTRFS_EXPERIMENTAL
+#ifdef CONFIG_BTRFS_READ_POLICIES
 
 /* Global module configuration parameters. */
 static char *read_policy;
@@ -1354,7 +1354,7 @@ int btrfs_read_policy_to_enum(const char *str, s64 *value_ret)
 
 	strscpy(param, str);
 
-#ifdef CONFIG_BTRFS_EXPERIMENTAL
+#ifdef CONFIG_BTRFS_READ_POLICIES
 	/* Separate value from input in policy:value format. */
 	value_str = strchr(param, ':');
 	if (value_str) {
@@ -1376,7 +1376,7 @@ int btrfs_read_policy_to_enum(const char *str, s64 *value_ret)
 	return sysfs_match_string(btrfs_read_policy_name, param);
 }
 
-#ifdef CONFIG_BTRFS_EXPERIMENTAL
+#ifdef CONFIG_BTRFS_READ_POLICIES
 int __init btrfs_read_policy_init(void)
 {
 	s64 value;
@@ -1407,7 +1407,7 @@ static ssize_t btrfs_read_policy_show(struct kobject *kobj,
 
 		ret += sysfs_emit_at(buf, ret, "%s", btrfs_read_policy_name[i]);
 
-#ifdef CONFIG_BTRFS_EXPERIMENTAL
+#ifdef CONFIG_BTRFS_READ_POLICIES
 		if (i == BTRFS_READ_POLICY_RR)
 			ret += sysfs_emit_at(buf, ret, ":%u",
 					     READ_ONCE(fs_devices->rr_min_contig_read));
@@ -1437,7 +1437,7 @@ static ssize_t btrfs_read_policy_store(struct kobject *kobj,
 	if (index < 0)
 		return -EINVAL;
 
-#ifdef CONFIG_BTRFS_EXPERIMENTAL
+#ifdef CONFIG_BTRFS_READ_POLICIES
 	/* If moving from RR then disable collecting fs stats. */
 	if (fs_devices->read_policy == BTRFS_READ_POLICY_RR && index != BTRFS_READ_POLICY_RR)
 		fs_devices->collect_fs_stats = false;

fs/btrfs/sysfs.h

@@ -50,7 +50,7 @@ void btrfs_sysfs_del_one_qgroup(struct btrfs_fs_info *fs_info,
 				struct btrfs_qgroup *qgroup);
 int btrfs_read_policy_to_enum(const char *str, s64 *value);
 
-#ifdef CONFIG_BTRFS_EXPERIMENTAL
+#ifdef CONFIG_BTRFS_READ_POLICIES
 int __init btrfs_read_policy_init(void);
 char *btrfs_get_mod_read_policy(void);
 #endif

fs/btrfs/volumes.c

@@ -1282,7 +1282,7 @@ static int open_fs_devices(struct btrfs_fs_devices *fs_devices,
 	fs_devices->latest_dev = latest_dev;
 	fs_devices->total_rw_bytes = 0;
 	fs_devices->chunk_alloc_policy = BTRFS_CHUNK_ALLOC_REGULAR;
-#ifdef CONFIG_BTRFS_EXPERIMENTAL
+#ifdef CONFIG_BTRFS_READ_POLICIES
 	fs_devices->rr_min_contig_read = BTRFS_DEFAULT_RR_MIN_CONTIG_READ;
 	fs_devices->read_devid = latest_dev->devid;
 	fs_devices->read_policy = btrfs_read_policy_to_enum(btrfs_get_mod_read_policy(),
@@ -6050,7 +6050,7 @@ unsigned long btrfs_full_stripe_len(struct btrfs_fs_info *fs_info,
 	return len;
 }
 
-#ifdef CONFIG_BTRFS_EXPERIMENTAL
+#ifdef CONFIG_BTRFS_READ_POLICIES
 static int btrfs_read_preferred(struct btrfs_chunk_map *map, int first, int num_stripes)
 {
 	for (int index = first; index < first + num_stripes; index++) {
@@ -6158,7 +6158,7 @@ static int find_live_mirror(struct btrfs_fs_info *fs_info,
 	case BTRFS_READ_POLICY_PID:
 		preferred_mirror = first + (current->pid % num_stripes);
 		break;
-#ifdef CONFIG_BTRFS_EXPERIMENTAL
+#ifdef CONFIG_BTRFS_READ_POLICIES
 	case BTRFS_READ_POLICY_RR:
 		preferred_mirror = btrfs_read_rr(map, first, num_stripes);
 		break;

fs/btrfs/volumes.h

@@ -318,7 +318,7 @@ enum btrfs_chunk_allocation_policy {
 enum btrfs_read_policy {
 	/* Use process PID to choose the stripe */
 	BTRFS_READ_POLICY_PID,
-#ifdef CONFIG_BTRFS_EXPERIMENTAL
+#ifdef CONFIG_BTRFS_READ_POLICIES
 	/* Balancing RAID1 reads across all striped devices (round-robin). */
 	BTRFS_READ_POLICY_RR,
 	/* Read from a specific device. */
@@ -463,7 +463,7 @@ struct btrfs_fs_devices {
 	/* Policy used to read the mirrored stripes. */
 	enum btrfs_read_policy read_policy;
 
-#ifdef CONFIG_BTRFS_EXPERIMENTAL
+#ifdef CONFIG_BTRFS_READ_POLICIES
 	/*
 	 * Minimum contiguous reads before switching to next device, the unit
 	 * is one block/sectorsize.
@@ -472,7 +472,9 @@ struct btrfs_fs_devices {
 
 	/* Device to be used for reading in case of RAID1. */
 	u64 read_devid;
+#endif
 
+#ifdef CONFIG_BTRFS_EXPERIMENTAL
 	/* Checksum mode - offload it or do it synchronously. */
 	enum btrfs_offload_csum_mode offload_csum_mode;
 #endif