[PATCH 0/2] btrfs: minor bs != ps cases fixes for free space tree enforcing

[PATCH 0/2] btrfs: minor bs != ps cases fixes for free space tree enforcing

[Qu Wenruo]

I'm update btrfs/131 to remove the v1 cache usage since v1 cache is
already marked deprecated.

With that update, I can run the test on bs < ps and bs > ps cases, the
formal failed due to the following reason:

- Free space cache is always enforced for bs < ps case
  Even if 'nospace_cache' mount option is provided.
  This is fixed by the first patch

And during tests I also exposed a minor problem for bs > ps cases:

- v1 cache mount is rejected for bs > ps cases
  That's because we lack the automatic free space tree enforcing for
  bs > ps cases.
  This is fixed by the second patch.

Qu Wenruo (2):
  btrfs: only enforce free space tree if v1 cache is required for bs <
    ps cases
  btrfs: forcing free space tree for bs > ps cases

 fs/btrfs/super.c | 12 +++++-------
 1 file changed, 5 insertions(+), 7 deletions(-)

-- 
2.52.0

[PATCH 1/2] btrfs: only enforce free space tree if v1 cache is required for bs < ps cases

[Qu Wenruo]

[BUG]
Since the introduction of btrfs bs < ps support, v1 cache is never on
the plan due to its hard coded PAGE_SIZE usage, and the future plan to
properly deprecate it.

However for bs < ps cases, even if 'nospace_cache,clear_cache' mount
option is specified, it's never respected and free space tree is always
enabled:

 mkfs.btrfs -f -O ^bgt,fst $dev
 mount $dev $mnt -o clear_cache,nospace_cache
 umount $mnt
 btrfs ins dump-super $dev
 ...
 compat_ro_flags		0x3
			( FREE_SPACE_TREE |
			  FREE_SPACE_TREE_VALID )
 ...

This means a different behavior compared to bs >= ps cases.

[CAUSE]
The forcing usage of v2 space cache is done inside
btrfs_set_free_space_cache_settings(), however it never checks if we're
even using space cache but always enabling v2 cache.

[FIX]
Instead unconditionally enable v2 cache, only forcing v2 cache if the
old v1 cache is required.

Now v2 space cache can be properly disabled on bs < ps cases:

 mkfs.btrfs -f -O ^bgt,fst $dev
 mount $dev $mnt -o clear_cache,nospace_cache
 umount $mnt
 btrfs ins dump-super $dev
 ...
 compat_ro_flags		0x0
 ...

Fixes: 9f73f1aef98b ("btrfs: force v2 space cache usage for subpage mount")
Signed-off-by: Qu Wenruo <wqu@suse.com>
---
 fs/btrfs/super.c | 12 +++++-------
 1 file changed, 5 insertions(+), 7 deletions(-)

diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c
index a37b71091014..09c38becf20b 100644
--- a/fs/btrfs/super.c
+++ b/fs/btrfs/super.c
@@ -736,14 +736,12 @@ bool btrfs_check_options(const struct btrfs_fs_info *info,
  */
 void btrfs_set_free_space_cache_settings(struct btrfs_fs_info *fs_info)
 {
-	if (fs_info->sectorsize < PAGE_SIZE) {
+	if (fs_info->sectorsize < PAGE_SIZE && btrfs_test_opt(fs_info, SPACE_CACHE)) {
+		btrfs_info(fs_info,
+			   "forcing free space tree for sector size %u with page size %lu",
+			   fs_info->sectorsize, PAGE_SIZE);
 		btrfs_clear_opt(fs_info->mount_opt, SPACE_CACHE);
-		if (!btrfs_test_opt(fs_info, FREE_SPACE_TREE)) {
-			btrfs_info(fs_info,
-				   "forcing free space tree for sector size %u with page size %lu",
-				   fs_info->sectorsize, PAGE_SIZE);
-			btrfs_set_opt(fs_info->mount_opt, FREE_SPACE_TREE);
-		}
+		btrfs_set_opt(fs_info->mount_opt, FREE_SPACE_TREE);
 	}
 
 	/*
-- 
2.52.0

[PATCH 2/2] btrfs: forcing free space tree for bs > ps cases

[Qu Wenruo]

[BUG]
Currently we only enforcing free space tree for bs < ps cases, but with
the recently added bs > ps support, we lack the free space tree
enforcing, causing explicit v1 cache mount option to fail on bs > ps
cases:

 # mount -o space_cache=v1 /dev/test/scratch1  /mnt/btrfs/
 mount: /mnt/btrfs: wrong fs type, bad option, bad superblock on /dev/mapper/test-scratch1, missing codepage or helper program, or other error.
        dmesg(1) may have more information after failed mount system call.

 # dmesg -t | tail -n7
 BTRFS: device fsid ac14a6fa-4ec9-449e-aec9-7d1777bfdc06 devid 1 transid 11 /dev/mapper/test-scratch1 (253:3) scanned by mount (2849)
 BTRFS info (device dm-3): first mount of filesystem ac14a6fa-4ec9-449e-aec9-7d1777bfdc06
 BTRFS info (device dm-3): using crc32c checksum algorithm
 BTRFS warning (device dm-3): support for block size 8192 with page size 4096 is experimental, some features may be missing
 BTRFS warning (device dm-3): space cache v1 is being deprecated and will be removed in a future release, please use -o space_cache=v2
 BTRFS warning (device dm-3): v1 space cache is not supported for page size 4096 with sectorsize 8192
 BTRFS error (device dm-3): open_ctree failed: -22

[FIX]
Just enable the same free space tree for bs > ps cases, aligning the
behavior to bs < ps cases.

Signed-off-by: Qu Wenruo <wqu@suse.com>
---
 fs/btrfs/super.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c
index 09c38becf20b..0a931555e6dc 100644
--- a/fs/btrfs/super.c
+++ b/fs/btrfs/super.c
@@ -736,7 +736,7 @@ bool btrfs_check_options(const struct btrfs_fs_info *info,
  */
 void btrfs_set_free_space_cache_settings(struct btrfs_fs_info *fs_info)
 {
-	if (fs_info->sectorsize < PAGE_SIZE && btrfs_test_opt(fs_info, SPACE_CACHE)) {
+	if (fs_info->sectorsize != PAGE_SIZE && btrfs_test_opt(fs_info, SPACE_CACHE)) {
 		btrfs_info(fs_info,
 			   "forcing free space tree for sector size %u with page size %lu",
 			   fs_info->sectorsize, PAGE_SIZE);
-- 
2.52.0

Re: [PATCH 0/2] btrfs: minor bs != ps cases fixes for free space tree enforcing

[Filipe Manana]

On Thu, Dec 18, 2025 at 4:46 AM Qu Wenruo <wqu@suse.com> wrote:
>
> I'm update btrfs/131 to remove the v1 cache usage since v1 cache is
> already marked deprecated.
>
> With that update, I can run the test on bs < ps and bs > ps cases, the
> formal failed due to the following reason:
>
> - Free space cache is always enforced for bs < ps case
>   Even if 'nospace_cache' mount option is provided.
>   This is fixed by the first patch
>
> And during tests I also exposed a minor problem for bs > ps cases:
>
> - v1 cache mount is rejected for bs > ps cases
>   That's because we lack the automatic free space tree enforcing for
>   bs > ps cases.
>   This is fixed by the second patch.
>
> Qu Wenruo (2):
>   btrfs: only enforce free space tree if v1 cache is required for bs <
>     ps cases
>   btrfs: forcing free space tree for bs > ps cases

Reviewed-by: Filipe Manana <fdmanana@suse.com>

Looks good, thanks.


>
>  fs/btrfs/super.c | 12 +++++-------
>  1 file changed, 5 insertions(+), 7 deletions(-)
>
> --
> 2.52.0
>
>