From: Liu Bo <bo.li.lu@xxxxxxxxxx>
This aims to decide whether a balance can reduce the number of
data block groups and if it can, this shows the '-dvrange' block
group's objectid.
With this, you can run
'btrfs balance start -c mnt' or 'btrfs balance start --check-only mnt'
--------------------------------------------------------------
$ btrfs balance start -c /mnt/btrfs
Checking data block groups...
block_group 12582912 (len 8388608 used 786432)
block_group 1103101952 (len 1073741824 used 536870912)
block_group 2176843776 (len 1073741824 used 1073741824)
total bgs 3 total_free 544473088 min_used bg 12582912 has (min_used 786432 free 7602176)
run 'btrfs balance start -dvrange=12582912..12582913 your_mnt'
$ btrfs balance start -dvrange=12582912..12582913 /mnt/btrfs
Done, had to relocate 1 out of 5 chunks
$ btrfs balance start -c /mnt/btrfs
Checking data block groups...
block_group 1103101952 (len 1073741824 used 537395200)
block_group 2176843776 (len 1073741824 used 1073741824)
total bgs 2 total_free 536346624 min_used bg 1103101952 has (min_used 537395200 free 536346624)
--------------------------------------------------------------
So you now know how to babysit your btrfs in a smart way.
Signed-off-by: Liu Bo <bo.li.liu@xxxxxxxxxx>
Signed-off-by: Ashish Samant <ashish.samant@xxxxxxxxxx>
---
cmds-balance.c | 127 +++++++++++++++++++++++++++++++++++++++++++++++++++++++-
1 files changed, 126 insertions(+), 1 deletions(-)
diff --git a/cmds-balance.c b/cmds-balance.c
index 8f3bf5b..e2aab6c 100644
--- a/cmds-balance.c
+++ b/cmds-balance.c
@@ -493,6 +493,116 @@ out:
return ret;
}
+/* return 0 if balance can remove a data block group, otherwise return 1 */
+static int search_data_bgs(const char *path)
+{
+ struct btrfs_ioctl_search_args args;
+ struct btrfs_ioctl_search_key *sk;
+ struct btrfs_ioctl_search_header *header;
+ struct btrfs_block_group_item *bg;
+ unsigned long off = 0;
+ DIR *dirstream = NULL;
+ int e;
+ int fd;
+ int i;
+ u64 total_free = 0;
+ u64 min_used = (u64)-1;
+ u64 free_of_min_used = 0;
+ u64 bg_of_min_used = 0;
+ u64 flags;
+ u64 used;
+ int ret = 0;
+ int nr_data_bgs = 0;
+
+ fd = btrfs_open_dir(path, &dirstream, 1);
+ if (fd < 0)
+ return 1;
+
+ memset(&args, 0, sizeof(args));
+ sk = &args.key;
+
+ sk->tree_id = BTRFS_EXTENT_TREE_OBJECTID;
+ sk->min_objectid = sk->min_offset = sk->min_transid = 0;
+ sk->max_objectid = sk->max_offset = sk->max_transid = (u64)-1;
+ sk->max_type = sk->min_type = BTRFS_BLOCK_GROUP_ITEM_KEY;
+ sk->nr_items = 65536;
+
+ while (1) {
+ ret = ioctl(fd, BTRFS_IOC_TREE_SEARCH, &args);
+ e = errno;
+ if (ret < 0) {
+ fprintf(stderr, "ret %d error '%s'\n", ret,
+ strerror(e));
+ return ret;
+ }
+ /*
+ * it should not happen.
+ */
+ if (sk->nr_items == 0)
+ break;
+
+ off = 0;
+ for (i = 0; i < sk->nr_items; i++) {
+ header = (struct btrfs_ioctl_search_header *)(args.buf
+ + off);
+
+ off += sizeof(*header);
+ if (header->type == BTRFS_BLOCK_GROUP_ITEM_KEY) {
+ bg = (struct btrfs_block_group_item *)
+ (args.buf + off);
+ flags = btrfs_block_group_flags(bg);
+ if (flags & BTRFS_BLOCK_GROUP_DATA) {
+ nr_data_bgs++;
+ used = btrfs_block_group_used(bg);
+ printf(
+ "block_group %15llu (len %11llu used %11llu)\n",
+ header->objectid,
+ header->offset, used);
+ total_free += header->offset - used;
+ if (min_used >= used) {
+ min_used = used;
+ free_of_min_used =
+ header->offset - used;
+ bg_of_min_used =
+ header->objectid;
+ }
+ }
+ }
+
+ off += header->len;
+ sk->min_objectid = header->objectid;
+ sk->min_type = header->type;
+ sk->min_offset = header->offset;
+ }
+ sk->nr_items = 65536;
+
+ if (sk->min_objectid < sk->max_objectid)
+ sk->min_objectid += 1;
+ else
+ break;
+ }
+
+ if (nr_data_bgs <= 1) {
+ printf("Data block groups in fs = %d, no need to do balance.\n",
+ nr_data_bgs);
+ return 1;
+ }
+
+ printf("total bgs %d total_free %llu min_used bg %llu has (min_used %llu free %llu)\n",
+ nr_data_bgs, total_free, bg_of_min_used, min_used,
+ free_of_min_used);
+ if (total_free - free_of_min_used > min_used) {
+ printf("run 'btrfs balance start -dvrange=%llu..%llu <mountpoint>'\n",
+ bg_of_min_used, bg_of_min_used + 1);
+ ret = 0;
+ } else {
+ printf("Please don't balance data block groups, it won't work.\n");
+ ret = 1;
+ }
+
+ return ret;
+}
+
static const char * const cmd_balance_start_usage[] = {
"btrfs balance start [options] <path>",
"Balance chunks across the devices",
@@ -508,6 +618,7 @@ static const char * const cmd_balance_start_usage[] = {
"-m[filters] act on metadata chunks",
"-s[filters] act on system chunks (only under -f)",
"-v be verbose",
+ "-c only check if balance would make sense, not doing real job",
"-f force reducing of metadata integrity",
"--full-balance do not print warning and do not delay start",
NULL
@@ -521,6 +632,7 @@ static int cmd_balance_start(int argc, char **argv)
int force = 0;
int verbose = 0;
unsigned start_flags = 0;
+ int check_data_bgs = 0;
int i;
memset(&args, 0, sizeof(args));
@@ -534,12 +646,14 @@ static int cmd_balance_start(int argc, char **argv)
{ "system", optional_argument, NULL, 's' },
{ "force", no_argument, NULL, 'f' },
{ "verbose", no_argument, NULL, 'v' },
+ { "check-only", no_argument, NULL, 'c' },
{ "full-balance", no_argument, NULL,
GETOPT_VAL_FULL_BALANCE },
{ NULL, 0, NULL, 0 }
};
- int opt = getopt_long(argc, argv, "d::s::m::fv", longopts, NULL);
+ int opt = getopt_long(argc, argv, "d::s::m::fvc", longopts,
+ NULL);
if (opt < 0)
break;
@@ -571,6 +685,9 @@ static int cmd_balance_start(int argc, char **argv)
case 'v':
verbose = 1;
break;
+ case 'c':
+ check_data_bgs = 1;
+ break;
case GETOPT_VAL_FULL_BALANCE:
start_flags |= BALANCE_START_NOWARN;
break;
@@ -582,6 +699,14 @@ static int cmd_balance_start(int argc, char **argv)
if (check_argc_exact(argc - optind, 1))
usage(cmd_balance_start_usage);
+ if (check_data_bgs) {
+ if (verbose)
+ dump_ioctl_balance_args(&args);
+
+ printf("Checking data block groups...\n");
+ return search_data_bgs(argv[optind]);
+ }
+
/*
* allow -s only under --force, otherwise do with system chunks
* the same thing we were ordered to do with meta chunks
--
1.7.1
--
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