Re: dm cache in BTRFS

[Mike Snitzer <snitzer@redhat.com>]

On Sat, Sep 20, 2025 at 09:11:02AM -0300, Augusto wrote:
> Hello.
> Thanks for reading that message.
> Please excuse if here not was the correct area to contact you.
> I use Linux with dm-cache writeback. You are the dm cache developer ? If yes
> thanks very much for making it.
> I want report an issue using dm-cache writeback with BTRFS.
> If the dm-cache writeback is full will happen an partial write of files in
> BTRFS file system and doing it create the terrible "Parent Transid Verify
> Failed" that in some times is fatal error.
> I understand that writeback cache can damage file system if not is done an
> full flush to disk, but BTRFS is extremely fragile compared with others file
> systems.
> I want continue using dm-cache writeback in BTRFS file system.
> Perhaps implementing an new feature in dm-cache that when the writeback
> cache is full is done an partial flush to disk in reference for some files
> in wb cache, but that partial number of files will be totally writen to disk
> avoiding partial writen of any file that is the because happen errors in
> BTRFS using wb cache.
> In others words if the cache is full will be done writen some files to disk
> with correct file size not doing partial flush to any file.
> In moment I not see any dm cache command setting to avoid that issue.
> Have an nice next week and excuse me if here not was the correct way to
> contact you about it.
> 

Please be specific about which DM targets you're using.

Please run and share output from:

  lsblk
  mount
  dmsetup table

But once you have that info, you'd do well to post any further
questions you might have to dm-devel@lists.linux.dev (now cc'd).

Thanks,
Mike