On 10/30/20 9:51 AM, Naohiro Aota wrote:
As updates to the space cache v1 are in-place, the space cache cannot be
located over sequential zones and there is no guarantees that the device
will have enough conventional zones to store this cache. Resolve this
problem by disabling completely the space cache v1. This does not
introduces any problems with sequential block groups: all the free space is
located after the allocation pointer and no free space before the pointer.
There is no need to have such cache.
Note: we can technically use free-space-tree (space cache v2) on ZONED
mode. But, since ZONED mode now always allocate extents in a block group
sequentially regardless of underlying device zone type, it's no use to
enable and maintain the tree.
For the same reason, NODATACOW is also disabled.
Also INODE_MAP_CACHE is also disabled to avoid preallocation in the
INODE_MAP_CACHE inode.
In summary, ZONED will disable:
| Disabled features | Reason |
|-------------------+-----------------------------------------------------|
| RAID/Dup | Cannot handle two zone append writes to different |
| | zones |
|-------------------+-----------------------------------------------------|
| space_cache (v1) | In-place updating |
| NODATACOW | In-place updating |
|-------------------+-----------------------------------------------------|
| fallocate | Reserved extent will be a write hole |
| INODE_MAP_CACHE | Need pre-allocation. (and will be deprecated?) |
|-------------------+-----------------------------------------------------|
| MIXED_BG | Allocated metadata region will be write holes for |
| | data writes |
Signed-off-by: Naohiro Aota <naohiro.aota@xxxxxxx>
---
fs/btrfs/super.c | 12 ++++++++++--
fs/btrfs/zoned.c | 18 ++++++++++++++++++
fs/btrfs/zoned.h | 5 +++++
3 files changed, 33 insertions(+), 2 deletions(-)
diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c
index 3312fe08168f..9064ca62b0a0 100644
--- a/fs/btrfs/super.c
+++ b/fs/btrfs/super.c
@@ -525,8 +525,14 @@ int btrfs_parse_options(struct btrfs_fs_info *info, char *options,
cache_gen = btrfs_super_cache_generation(info->super_copy);
if (btrfs_fs_compat_ro(info, FREE_SPACE_TREE))
btrfs_set_opt(info->mount_opt, FREE_SPACE_TREE);
- else if (cache_gen)
- btrfs_set_opt(info->mount_opt, SPACE_CACHE);
+ else if (cache_gen) {
+ if (btrfs_is_zoned(info)) {
+ btrfs_info(info,
+ "clearring existing space cache in ZONED mode");
'clearing', and then you can add
Reviewed-by: Josef Bacik <josef@xxxxxxxxxxxxxx>
Thanks,
Josef
