[BUG]
When creating btrfs with new v2 cache (the default behavior), mkfs.btrfs
always create the free space tree using bitmap.
It's fine for small fs, but will be a disaster if the device is large
and the data profile is something like RAID0:
$ mkfs.btrfs -f -m raid1 -d raid0 /dev/test/scratch[1234]
btrfs-progs v5.17
[...]
Block group profiles:
Data: RAID0 4.00GiB
Metadata: RAID1 256.00MiB
System: RAID1 8.00MiB
[..]
$ btrfs ins dump-tree -t free-space /dev/test/scratch1
btrfs-progs v5.17
free space tree key (FREE_SPACE_TREE ROOT_ITEM 0)
node 30441472 level 1 items 10 free space 483 generation 6 owner FREE_SPACE_TREE
node 30441472 flags 0x1(WRITTEN) backref revision 1
fs uuid deddccae-afd0-4160-9a12-48fe7b526fb1
chunk uuid 68f6cf98-afe3-4f47-9797-37fd9c610219
key (1048576 FREE_SPACE_INFO 4194304) block 30457856 gen 6
key (475004928 FREE_SPACE_BITMAP 8388608) block 30703616 gen 5
key (953155584 FREE_SPACE_BITMAP 8388608) block 30720000 gen 5
key (1431306240 FREE_SPACE_BITMAP 8388608) block 30736384 gen 5
key (1909456896 FREE_SPACE_BITMAP 8388608) block 30752768 gen 5
key (2387607552 FREE_SPACE_BITMAP 8388608) block 30769152 gen 5
key (2865758208 FREE_SPACE_BITMAP 8388608) block 30785536 gen 5
key (3343908864 FREE_SPACE_BITMAP 8388608) block 30801920 gen 5
key (3822059520 FREE_SPACE_BITMAP 8388608) block 30818304 gen 5
key (4300210176 FREE_SPACE_BITMAP 8388608) block 30834688 gen 5
[...]
^^^ So many bitmaps that an empty fs will have two levels for free
space tree already
[CAUSE]
Member btrfs_block_group::bitmap_high_thresh is never properly set to
any value other than 0, thus in function
update_free_space_extent_count(), the following check is always true:
if (!(flags & BTRFS_FREE_SPACE_USING_BITMAPS) &&
extent_count > block_group->bitmap_high_thresh) {
ret = convert_free_space_to_bitmaps(trans, block_group, path);
Thus we always got converted to bitmaps.
[FIX]
Cross-port the function set_free_space_tree_thresholds() from kernel,
and call that function in btrfs_make_block_group() and
read_one_block_group() so that every block group has bitmap_high_thresh
properly set.
Now even for that 4GiB large data chunk, we still only have one free extent:
btrfs-progs v5.17
free space tree key (FREE_SPACE_TREE ROOT_ITEM 0)
leaf 30572544 items 15 free space 15860 generation 6 owner FREE_SPACE_TREE
leaf 30572544 flags 0x1(WRITTEN) backref revision 1
fs uuid b24e52ea-6580-4a88-aa70-cb173090bfe3
chunk uuid d85f3905-fc61-4084-b335-2b6b97814b8e
[...]
item 13 key (298844160 FREE_SPACE_INFO 4294967296) itemoff 16235 itemsize 8
free space info extent count 1 flags 0
item 14 key (298844160 FREE_SPACE_EXTENT 4294967296) itemoff 16235 itemsize 0
free space extent
Signed-off-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
This exists in the kernel free-space-tree.c but not in progs. We need
it to generate the free space items for new block groups, which is
needed when we start creating the free space tree in make_btrfs().
Signed-off-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: David Sterba <dsterba@suse.com>
