On 7/1/20 8:14 PM, Qu Wenruo wrote:
Since commit c6887cd11149 ("Btrfs: don't do nocow check unless we have to"),
btrfs/153 always fails with early EDQUOT.
This is caused by the fact that:
- We always reserved data space for even NODATACOW buffered write
This is mostly to improve performance, and not pratical to revert.
- Btrfs qgroup data and meta reserved space share the same limit
So it's not ensured to return EDQUOT just for that data reservation,
metadata reservation can also get EDQUOT, means we can't go the same
solution as that commit.
This patchset will solve it by doing extra qgroup space flushing when
EDQUOT is hit.
This is a little like what we do in ticketing space reservation system,
but since there are very limited ways for qgroup to reclaim space,
currently it's still handled in qgroup realm, not reusing the ticketing
system yet.
By this, this patch could solve the btrfs/153 problem, while still keep
btrfs qgroup space usage under the limit.
The only cost is, when we're near qgroup limit, we will cause more dirty
inodes flush and transaction commit, much like what we do when the
metadata space is near exhausted.
So the cost should be still acceptable.
This patchset fails to apply on misc-next as of
btrfs: allow use of global block reserve for balance item deletion
Thanks,
Josef
