Re: [PATCH v2 7/7] btrfs-progs: btrfstune: Allow to enable bg-tree feature offline

Anand Jain
2019-10-17T04:17:39Z

Depending on the size of the FS the convert may take longer, further
fatal error (power loss; pid kill) may leave the FS in a state where
the bg items are in both extent-tree and bg-tree.

The lessons which lead to the implementation of metadata_uuid fsid
suggests, for conversions its better to use the btrfstune to only
flag the bg convert requirement and let the kernel handle of migration
of the bg items from the extent-tree to the bg-tree as and when the
bg-items are written.

Thanks, Anand

On 10/8/19 12:49 PM, Qu Wenruo wrote:
> Add a new option '-b' for btrfstune, to enable bg-tree feature for a
> unmounted fs.
>
> This feature will convert all BLOCK_GROUP_ITEMs in extent tree to bg
> tree, by reusing the existing btrfs_convert_to_bg_tree() function.
>
> Signed-off-by: Qu Wenruo <wqu@suse.com>
> ---
> Documentation/btrfstune.asciidoc | 6 +++++
> btrfstune.c | 44 ++++++++++++++++++++++++++++++--
> 2 files changed, 48 insertions(+), 2 deletions(-)
>
> diff --git a/Documentation/btrfstune.asciidoc b/Documentation/btrfstune.asciidoc
> index 1d6bc98deed8..ed54c2e1597f 100644
> --- a/Documentation/btrfstune.asciidoc
> +++ b/Documentation/btrfstune.asciidoc
> @@ -26,6 +26,12 @@ means. Please refer to the 'FILESYSTEM FEATURES' in `btrfs`(5).
> OPTIONS
> -------
>
> +-b::
> +(since kernel: 5.x)
> ++
> +enable bg-tree feature (faster mount time for large fs), enabled by mkfs
> +feature 'bg-tree'.
> +
> -f::
> Allow dangerous changes, e.g. clear the seeding flag or change fsid. Make sure
> that you are aware of the dangers.
> diff --git a/btrfstune.c b/btrfstune.c
> index afa3aae35412..aa1ac568aef0 100644
> --- a/btrfstune.c
> +++ b/btrfstune.c
> @@ -476,11 +476,39 @@ static void print_usage(void)
> printf("\t-m change fsid in metadata_uuid to a random UUID\n");
> printf("\t (incompat change, more lightweight than -u|-U)\n");
> printf("\t-M UUID change fsid in metadata_uuid to UUID\n");
> + printf("\t-b enable bg-tree feature (mkfs: bg-tree, for faster mount time)\n");
> printf(" general:\n");
> printf("\t-f allow dangerous operations, make sure that you are aware of the dangers\n");
> printf("\t--help print this help\n");
> }
>
> +static int convert_to_bg_tree(struct btrfs_fs_info *fs_info)
> +{
> + struct btrfs_trans_handle *trans;
> + int ret;
> +
> + trans = btrfs_start_transaction(fs_info->tree_root, 1);
> + if (IS_ERR(trans)) {
> + ret = PTR_ERR(trans);
> + errno = -ret;
> + error("failed to start transaction: %m");
> + return ret;
> + }
> + ret = btrfs_convert_to_bg_tree(trans);
> + if (ret < 0) {
> + errno = -ret;
> + error("failed to convert: %m");
> + btrfs_abort_transaction(trans, ret);
> + return ret;
> + }
> + ret = btrfs_commit_transaction(trans, fs_info->tree_root);
> + if (ret < 0) {
> + errno = -ret;
> + error("failed to commit transaction: %m");
> + }
> + return ret;
> +}
> +
> int BOX_MAIN(btrfstune)(int argc, char *argv[])
> {
> struct btrfs_root *root;
> @@ -491,6 +519,7 @@ int BOX_MAIN(btrfstune)(int argc, char *argv[])
> u64 seeding_value = 0;
> int random_fsid = 0;
> int change_metadata_uuid = 0;
> + bool to_bg_tree = false;
> char *new_fsid_str = NULL;
> int ret;
> u64 super_flags = 0;
> @@ -501,7 +530,7 @@ int BOX_MAIN(btrfstune)(int argc, char *argv[])
> { "help", no_argument, NULL, GETOPT_VAL_HELP},
> { NULL, 0, NULL, 0 }
> };
> - int c = getopt_long(argc, argv, "S:rxfuU:nmM:", long_options, NULL);
> + int c = getopt_long(argc, argv, "S:rxfuU:nmM:b", long_options, NULL);
>
> if (c < 0)
> break;
> @@ -539,6 +568,9 @@ int BOX_MAIN(btrfstune)(int argc, char *argv[])
> ctree_flags |= OPEN_CTREE_IGNORE_FSID_MISMATCH;
> change_metadata_uuid = 1;
> break;
> + case 'b':
> + to_bg_tree = true;
> + break;
> case GETOPT_VAL_HELP:
> default:
> print_usage();
> @@ -556,7 +588,7 @@ int BOX_MAIN(btrfstune)(int argc, char *argv[])
> return 1;
> }
> if (!super_flags && !seeding_flag && !(random_fsid || new_fsid_str) &&
> - !change_metadata_uuid) {
> + !change_metadata_uuid && !to_bg_tree) {
> error("at least one option should be specified");
> print_usage();
> return 1;
> @@ -602,6 +634,14 @@ int BOX_MAIN(btrfstune)(int argc, char *argv[])
> return 1;
> }
>
> + if (to_bg_tree) {
> + ret = convert_to_bg_tree(root->fs_info);
> + if (ret < 0) {
> + errno = -ret;
> + error("failed to convert to bg-tree feature: %m");
> + goto out;
> + }
> + }
> if (seeding_flag) {
> if (btrfs_fs_incompat(root->fs_info, METADATA_UUID)) {
> fprintf(stderr, "SEED flag cannot be changed on a metadata-uuid changed fs\n");
>