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Date: Mon, 14 Oct 2024 18:24:16 +0500
From: Roman Mamedov <rm@romanrm.net>
To: linux-btrfs@vger.kernel.org
Subject: Issue remounting from compress-force to compress
Message-ID: <20241014182416.13d0f8b0@nvm>
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Hello,

Just faced this when trying to change a mounted FS from compress-force to just compress.

Initial state:

  # mount | grep btrfs
  /dev/mapper/wd-p1 on /mnt/p1 type btrfs (rw,relatime,compress-force=zstd:9,discard=async,space_cache=v2,subvolid=5,subvol=/)

Remounting:

  # mount /mnt/p1 -o remount,compress=zstd:9

But no effect:

  # mount | grep btrfs
  /dev/mapper/wd-p1 on /mnt/p1 type btrfs (rw,relatime,compress-force=zstd:9,discard=async,space_cache=v2,subvolid=5,subvol=/)

OK, remounting to no compression:

  # mount /mnt/p1 -o remount,compress-force=none

Success:

  # mount | grep btrfs
  /dev/mapper/wd-p1 on /mnt/p1 type btrfs (rw,relatime,discard=async,space_cache=v2,subvolid=5,subvol=/)

Now, I expect to enable just compress:

  # mount /mnt/p1 -o remount,compress=zstd:9

But suddenly, compress-force is enabled again instead:

  # mount | grep btrfs
  /dev/mapper/wd-p1 on /mnt/p1 type btrfs (rw,relatime,compress-force=zstd:9,discard=async,space_cache=v2,subvolid=5,subvol=/)

This is unexpected and seems like a bug.

The only way to achieve what I wanted was:

  # mount /mnt/p1 -o remount,compress-force=none,compress=zstd:9
  
  # mount | grep btrfs
  /dev/mapper/wd-p1 on /mnt/p1 type btrfs (rw,relatime,compress=zstd:9,discard=async,space_cache=v2,subvolid=5,subvol=/)

Kernel version is 6.8.12-2-pve (Proxmox).

-- 
With respect,
Roman