Sorry for the confusing cover letter title.
This patch is no longer RFC now.
It's already a working one, and we're doing stress test to ensure it's
completely OK, but seems quite good for now.
To Chris,
I know the timing I sent the patchset is quite awful, as there is only
less than 1 week for rc1, and the merge window will close soon.
But I still hope there would be a small chance we can merge it into
early v4.3-rc. Maybe rc2 or rc3?
As the reserve space leaking problem is quite annoying, sometimes even
making qgroup limit unusable.
If that's not possible, I'm completely OK with that though, as Linus
won't be happy about that without doubt.
Thanks,
Qu
Qu Wenruo wrote on 2015/09/08 16:56 +0800:
[[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(-)
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