[PATCH RFC 00/14] Accurate qgroup reserve framework

From: Qu Wenruo <quwenruo@cn.fujitsu.com>
To: linux-btrfs@vger.kernel.org
Subject: [PATCH RFC 00/14] Accurate qgroup reserve framework
Date: Tue,  8 Sep 2015 16:37:17 +0800	[thread overview]
Message-ID: <1441701456-8034-1-git-send-email-quwenruo@cn.fujitsu.com> (raw)

[[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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2.5.1