RFE: Online thin_trim

[DemiMarie]

thin_trim currently needs to run offline, which is quite inconvienent. It would be much more convienent if thin_trim could be used online.

[mingnus]

it's the limitation of the tool and dm-thin. Unlike fstrim, thin_trim performs discard from userland, and the dm-thin driver does not lock unused data blocks during the process. That's why thin_trim requires the pool to be offline.

An (inefficient) workaround might be, create a new volume that occupies the amount of free space you'd like to discard in the pool, then discard the whole volume to passdown the trim commands to the pool data device. However, this approach results in unnecessary writes due to the allocations, although we don't have to write the whole data block.

[DemiMarie]

it's the limitation of the tool and dm-thin. Unlike fstrim, thin_trim performs discard from userland, and the dm-thin driver does not lock unused data blocks during the process. That's why thin_trim requires the pool to be offline.

Could this be fixed in dm-thin?

An (inefficient) workaround might be, create a new volume that occupies the amount of free space you'd like to discard in the pool, then discard the whole volume to passdown the trim commands to the pool data device. However, this approach results in unnecessary writes due to the allocations, although we don't have to write the whole data block.

Another approach might be to suspend the entire pool while the discard operation happens.