[[BUG]] One of the most common case to trigger the bug is the following method: 1) Enable quota 2) Limit excl of qgroup 5 to 16M 3) Write [0,2M) of a file inside subvol 5 10 times without sync
EQUOT will be triggered at about the 8th write. [[CAUSE]] The problem is caused by the fact that qgroup will reserve space even the data space is already reserved. In above reproducer, each time we buffered write [0,2M) qgroup will reserve 2M space, but in fact, at the 1st time, we have already reserved 2M and from then on, we don't need to reserved any data space as we are only writing [0,2M). Also, the reserved space will only be freed *ONCE* when its backref is run at commit_transaction() time. That's causing the reserved space leaking. [[FIX]] The fix is not a simple one, as currently btrfs_qgroup_reserve() follow the very bad btrfs space allocating principle: Allocate as much as you needed, even it's not fully used. So for accurate qgroup reserve, we introduce a completely new framework for data and metadata. 1) Per-inode data reserve map Now, each inode will have a data reserve map, recording which range of data is already reserved. If we are writing a range which is already reserved, we won't need to reserve space again. Also, for the fact that qgroup is only accounted at commit_trans(), for data commit into disc and its metadata is also inserted into current tree, we should free the data reserved range, but still keep the reserved space until commit_trans(). So delayed_ref_head will have new members to record how much space is reserved and free them at commit_trans() time. 2) Per-root metadata reserve counter For metadata(tree block), it's impossible to know how much space it will use exactly in advance. And due to the new qgroup accounting framework, the old free-at-end-trans may lead to exceeding limit. So we record how much metadata space is reserved for each root, and free them at commit_trans() time. This method is not perfect, but thanks to the compared small size of metadata, it should be quite good. More detailed info can be found in each commit message and source commend. Qu Wenruo (19): btrfs: qgroup: New function declaration for new reserve implement btrfs: qgroup: Implement data_rsv_map init/free functions btrfs: qgroup: Introduce new function to search most left reserve range btrfs: qgroup: Introduce function to insert non-overlap reserve range btrfs: qgroup: Introduce function to reserve data range per inode btrfs: qgroup: Introduce btrfs_qgroup_reserve_data function btrfs: qgroup: Introduce function to release reserved range btrfs: qgroup: Introduce function to release/free reserved data range btrfs: delayed_ref: Add new function to record reserved space into delayed ref btrfs: delayed_ref: release and free qgroup reserved at proper timing btrfs: qgroup: Introduce new functions to reserve/free metadata btrfs: qgroup: Use new metadata reservation. btrfs: extent-tree: Add new verions of btrfs_check_data_free_space btrfs: Switch to new check_data_free_space btrfs: fallocate: Add support to accurate qgroup reserve btrfs: extent-tree: Add new version of btrfs_delalloc_reserve_space btrfs: extent-tree: Use new __btrfs_delalloc_reserve_space function btrfs: qgroup: Cleanup old inaccurate facilities btrfs: qgroup: Add handler for NOCOW and inline fs/btrfs/btrfs_inode.h | 6 + fs/btrfs/ctree.h | 8 +- fs/btrfs/delayed-ref.c | 29 +++ fs/btrfs/delayed-ref.h | 14 + fs/btrfs/disk-io.c | 1 + fs/btrfs/extent-tree.c | 99 +++++--- fs/btrfs/file.c | 169 +++++++++---- fs/btrfs/inode-map.c | 2 +- fs/btrfs/inode.c | 51 +++- fs/btrfs/ioctl.c | 3 +- fs/btrfs/qgroup.c | 674 ++++++++++++++++++++++++++++++++++++++++++++++++- fs/btrfs/qgroup.h | 18 +- fs/btrfs/transaction.c | 34 +-- fs/btrfs/transaction.h | 1 - 14 files changed, 979 insertions(+), 130 deletions(-) -- 2.5.1 -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html