Btrfs needs to read out all block group (bg) items to fill its bg
caches.
However such bg caches are only needed for read-write mount, and makes
no sense for RO mount.
So this patch introduce new mount option, skip_bg, to skip block group
items scan.
This new 'skip_bg' mount option can only be used with TRUE read-only
mount, which needs the following dependency:
- RO mount
Obviously.
- No log tree or notreelog mount option
- No way to remoutn RW
Similar to notreelog mount option.
- No chunk <-> bg <-> dev extents restrict check
This option should only be used as kernel equivalent of btrfs-restore.
With this patch, we can even mount a btrfs whose extent root is
completely corrupted.
But can also be an option to test if btrfs_read_block_groups() is the
major cause for slow btrfs mount.
Signed-off-by: Qu Wenruo <w...@suse.com>
---
fs/btrfs/ctree.h | 1 +
fs/btrfs/disk-io.c | 29 ++++++++++++++++++---
fs/btrfs/extent-tree.c | 59 ++++++++++++++++++++++++++++++++++++++++++
fs/btrfs/super.c | 20 ++++++++++++++
fs/btrfs/volumes.c | 7 +++++
5 files changed, 112 insertions(+), 4 deletions(-)
diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
index 80953528572d..371b5e2f6fbe 100644
--- a/fs/btrfs/ctree.h
+++ b/fs/btrfs/ctree.h
@@ -1353,6 +1353,7 @@ static inline u32 BTRFS_MAX_XATTR_SIZE(const struct
btrfs_fs_info *info)
#define BTRFS_MOUNT_FREE_SPACE_TREE (1 << 26)
#define BTRFS_MOUNT_NOLOGREPLAY (1 << 27)
#define BTRFS_MOUNT_REF_VERIFY (1 << 28)
+#define BTRFS_MOUNT_SKIP_BG (1 << 29)
#define BTRFS_DEFAULT_COMMIT_INTERVAL (30)
#define BTRFS_DEFAULT_MAX_INLINE (2048)
diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index b0ab41da91d1..5228320030a5 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -2330,11 +2330,15 @@ static int btrfs_read_roots(struct btrfs_fs_info
*fs_info)
root = btrfs_read_tree_root(tree_root, &location);
if (IS_ERR(root)) {
- ret = PTR_ERR(root);
- goto out;
+ if (!btrfs_test_opt(fs_info, SKIP_BG)) {
+ ret = PTR_ERR(root);
+ goto out;
+ }
+ fs_info->extent_root = NULL;
+ } else {
+ set_bit(BTRFS_ROOT_TRACK_DIRTY, &root->state);
+ fs_info->extent_root = root;
}
- set_bit(BTRFS_ROOT_TRACK_DIRTY, &root->state);
- fs_info->extent_root = root;
location.objectid = BTRFS_DEV_TREE_OBJECTID;
root = btrfs_read_tree_root(tree_root, &location);
@@ -2927,6 +2931,23 @@ int open_ctree(struct super_block *sb,
goto fail_alloc;
}
+ /* Skip bg needs RO and no log tree replay */
+ if (btrfs_test_opt(fs_info, SKIP_BG)) {
+ if (!sb_rdonly(sb)) {
+ btrfs_err(fs_info,
+ "skip_bg mount option can only be used with read-only mount");
+ err = -EINVAL;
+ goto fail_alloc;
+ }
+ if (btrfs_super_log_root(disk_super) &&
+ !btrfs_test_opt(fs_info, NOTREELOG)) {
+ btrfs_err(fs_info,
+ "skip_bg must be used with notreelog mount option for dirty log");
+ err = -EINVAL;
+ goto fail_alloc;
+ }
+ }
+
ret = btrfs_init_workqueues(fs_info, fs_devices);
if (ret) {
err = ret;
diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index a1febf155747..051a5a63c2b0 100644
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -9948,6 +9948,62 @@ static int check_chunk_block_group_mappings(struct
btrfs_fs_info *fs_info)
return ret;
}
+static int fill_dummy_bgs(struct btrfs_fs_info *fs_info)
+{
+ struct extent_map_tree *em_tree = &fs_info->mapping_tree.map_tree;
+ struct extent_map *em;
+ struct map_lookup *map;
+ struct btrfs_block_group_cache *cache;
+ struct btrfs_space_info *space_info;
+ struct rb_node *node;
+ int ret = 0;
+
+ read_lock(&em_tree->lock);
+ for (node = rb_first_cached(&em_tree->map); node;
+ node = rb_next(node)) {
+ em = rb_entry(node, struct extent_map, rb_node);
+ map = em->map_lookup;
+ cache = btrfs_create_block_group_cache(fs_info, em->start,
+ em->len);
+ if (!cache) {
+ ret = -ENOMEM;
+ goto out;
+ }
+
+ /* Fill dummy cache as FULL */
+ cache->flags = map->type;
+ cache->last_byte_to_unpin = (u64)-1;
+ cache->cached = BTRFS_CACHE_FINISHED;
+ btrfs_set_block_group_used(&cache->item, em->len);
+ btrfs_set_block_group_chunk_objectid(&cache->item, em->start);
+ btrfs_set_block_group_flags(&cache->item, map->type);
+ ret = exclude_super_stripes(cache);
+ if (ret) {
+ free_excluded_extents(cache);
+ btrfs_put_block_group(cache);
+ goto out;
+ }
+ free_excluded_extents(cache);
+ ret = btrfs_add_block_group_cache(fs_info, cache);
+ if (ret) {
+ btrfs_remove_free_space_cache(cache);
+ btrfs_put_block_group(cache);
+ goto out;
+ }
+ update_space_info(fs_info, cache->flags, em->start, em->len,
+ cache->bytes_super, &space_info);
+ cache->space_info = space_info;
+ link_block_group(cache);
+
+ set_avail_alloc_bits(fs_info, cache->flags);
+ if (btrfs_chunk_readonly(fs_info, em->start))
+ inc_block_group_ro(cache, 1);
+ }
+out:
+ read_unlock(&em_tree->lock);
+ return ret;
+}
+
int btrfs_read_block_groups(struct btrfs_fs_info *info)
{
struct btrfs_path *path;
@@ -9962,6 +10018,9 @@ int btrfs_read_block_groups(struct btrfs_fs_info *info)
u64 feature;
int mixed;
+ if (btrfs_test_opt(info, SKIP_BG))
+ return fill_dummy_bgs(info);
+
feature = btrfs_super_incompat_flags(info->super_copy);
mixed = !!(feature & BTRFS_FEATURE_INCOMPAT_MIXED_GROUPS);
diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c
index b362b45dd757..5bc751819b19 100644
--- a/fs/btrfs/super.c
+++ b/fs/btrfs/super.c
@@ -337,6 +337,7 @@ enum {
Opt_check_integrity_including_extent_data,
Opt_check_integrity_print_mask,
Opt_enospc_debug, Opt_noenospc_debug,
+ Opt_skip_bg,
#ifdef CONFIG_BTRFS_DEBUG
Opt_fragment_data, Opt_fragment_metadata, Opt_fragment_all,
#endif
@@ -393,6 +394,7 @@ static const match_table_t tokens = {
{Opt_notreelog, "notreelog"},
{Opt_usebackuproot, "usebackuproot"},
{Opt_user_subvol_rm_allowed, "user_subvol_rm_allowed"},
+ {Opt_skip_bg, "skip_bg"},
/* Deprecated options */
{Opt_alloc_start, "alloc_start=%s"},
@@ -664,6 +666,10 @@ int btrfs_parse_options(struct btrfs_fs_info *info, char
*options,
btrfs_clear_and_info(info, NOTREELOG,
"enabling tree log");
break;
+ case Opt_skip_bg:
+ btrfs_set_and_info(info, SKIP_BG,
+ "skip mount time block groupo searching");
+ break;
case Opt_norecovery:
case Opt_nologreplay:
btrfs_set_and_info(info, NOLOGREPLAY,
@@ -1797,6 +1803,13 @@ static int btrfs_remount(struct super_block *sb, int
*flags, char *data)
if (ret)
goto restore;
+ if (btrfs_test_opt(fs_info, SKIP_BG) !=
+ (old_opts & BTRFS_MOUNT_SKIP_BG)) {
+ btrfs_err(fs_info,
+ "skip_bg mount option can't be changed during remount");
+ ret = -EINVAL;
+ goto restore;
+ }
btrfs_remount_begin(fs_info, old_opts, *flags);
btrfs_resize_thread_pool(fs_info,
fs_info->thread_pool_size, old_thread_pool_size);
@@ -1858,6 +1871,13 @@ static int btrfs_remount(struct super_block *sb, int
*flags, char *data)
goto restore;
}
+ if (btrfs_test_opt(fs_info, SKIP_BG)) {
+ btrfs_err(fs_info,
+ "remounting read-write with skip_bg is not allowed");
+ ret = -EINVAL;
+ goto restore;
+ }
+
ret = btrfs_cleanup_fs_roots(fs_info);
if (ret)
goto restore;
diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index f435d397019e..d614b2fab652 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -7480,6 +7480,13 @@ int btrfs_verify_dev_extents(struct btrfs_fs_info
*fs_info)
struct btrfs_key key;
int ret = 0;
+ /*
+ * For skip_bg mount option, we're already RO and are salvaging data,
+ * no need for such restrict check.
+ */
+ if (btrfs_test_opt(fs_info, SKIP_BG))
+ return 0;
+
key.objectid = 1;
key.type = BTRFS_DEV_EXTENT_KEY;
key.offset = 0;
--
2.20.1
