On 2019/1/23 下午3:15, Qu Wenruo wrote: > This patchset can be fetched from github: > https://github.com/adam900710/linux/tree/qgroup_delayed_subtree > > Which is based on v5.0-rc1. > > This patch address the heavy load subtree scan, but delaying it until > we're going to modify the swapped tree block. > > The overall workflow is: > > 1) Record the subtree root block get swapped. > > During subtree swap: > O = Old tree blocks > N = New tree blocks > reloc tree subvol tree X > Root Root > / \ / \ > NA OB OA OB > / | | \ / | | \ > NC ND OE OF OC OD OE OF > > In these case, NA and OA is going to be swapped, record (NA, OA) into > subvol tree X. > > 2) After subtree swap. > reloc tree subvol tree X > Root Root > / \ / \ > OA OB NA OB > / | | \ / | | \ > OC OD OE OF NC ND OE OF > > 3a) CoW happens for OB > If we are going to CoW tree block OB, we check OB's bytenr against > tree X's swapped_blocks structure. > It doesn't fit any one, nothing will happen. > > 3b) CoW happens for NA > Check NA's bytenr against tree X's swapped_blocks, and get a hit. > Then we do subtree scan on both subtree OA and NA. > Resulting 6 tree blocks to be scanned (OA, OC, OD, NA, NC, ND). > > Then no matter what we do to subvol tree X, qgroup numbers will > still be correct. > Then NA's record get removed from X's swapped_blocks. > > 4) Transaction commit > Any record in X's swapped_blocks get removed, since there is no > modification to swapped subtrees, no need to trigger heavy qgroup > subtree rescan for them. > > [[Benchmark]] (*) > Hardware: > VM 4G vRAM, 8 vCPUs, > disk is using 'unsafe' cache mode, > backing device is SAMSUNG 850 evo SSD. > Host has 16G ram. > > Mkfs parameter: > --nodesize 4K (To bump up tree size) > > Initial subvolume contents: > 4G data copied from /usr and /lib. > (With enough regular small files) > > Snapshots: > 16 snapshots of the original subvolume. > each snapshot has 3 random files modified. > > balance parameter: > -m > > So the content should be pretty similar to a real world root fs layout. > > And after file system population, there is no other activity, so it > should be the best case scenario. > > | v4.20-rc1 | w/ patchset | diff > ----------------------------------------------------------------------- > relocated extents | 22615 | 22457 | -0.1% > qgroup dirty extents | 163457 | 121606 | -25.6% > time (sys) | 22.884s | 18.842s | -17.6% > time (real) | 27.724s | 22.884s | -17.5% > > *: Due to a bug in v5.0-rc1, balancing metadata with snapshots is > unacceptably slow even with quota disabled. So the result is from > v4.20-rc1. > > changelog: > v2: > - Rebase to v4.20-rc1. > > - Instead commit transaction after each reloc tree merge, delay it until > merge_reloc_roots() finishes. > This provides a more natural behavior, and reduce the unnecessary > transaction commits. > > v3: > - Fix backref walk deadlock by not triggering it at all. > This also removes the need for @exec_post refactor and replace the > patch to allow @old_root unpopulated. > > - Include the patch that fixes the unexpected data rsv free. > > v3.1: > - Rebased to v4.20-rc1. > Minor conflicts with some cleanup code. > > v4: > - Renaming members from "file_*" to "subv_*". > Members like "file_bytenr" is pretty confusing, renaming it to > "subv_bytenr" avoid the confusion. > > - Use btrfs_root::reloc_dirty_list to replace dynamic memory allocation > One less point of failure, and no need to worry about GFP_KERNEL/NOFS. > Furthermore, it's easier to manipulate list than rb tree. > > v5: > - Use Josef's superior qgroup deadlock fix. > No performance regression now. > > - A new patch to allow delayed subtree rescan to insert empty old_roots.
I should double check the cover letter.
This part is incorrect, please just ignore it.
Thanks,
Qu
>
> - Fix a possible race due to wrong rb_tree node initialization out of
> critical section.
>
> - A lot of coding style fixes:
> * naming change from "file"/"subv" to "subvol"
> * {} for any else if branch
> * avoid err/ret confusion by introducing "tmp_ret"
> * proper errno for non-uptodate extent buffer
> * struct member re-ordering to avoid unnecessary padding
> * avoid single letter variable name
> * less redundant emphasizing
> * move certain devel-only warning under CONFIG_BTRFS_DEBUG
> * replace cool-sounding 'hack' with 'optimization'
> * remove unnecessary inline prefix for btrfs_qgroup_init_swapped_blocks
> * keep an empty line before #endif
>
>
> Josef Bacik (1):
> btrfs: honor path->skip_locking in backref code
>
> Qu Wenruo (6):
> btrfs: qgroup: Move reserved data account from btrfs_delayed_ref_head
> to btrfs_qgroup_extent_record
> btrfs: relocation: Delay reloc tree deletion after merge_reloc_roots()
> btrfs: qgroup: Refactor btrfs_qgroup_trace_subtree_swap()
> btrfs: qgroup: Introduce per-root swapped blocks infrastructure
> btrfs: qgroup: Use delayed subtree rescan for balance
> btrfs: qgroup: Cleanup old subtree swap code
>
> fs/btrfs/backref.c | 16 +-
> fs/btrfs/ctree.c | 8 +
> fs/btrfs/ctree.h | 29 +++
> fs/btrfs/delayed-ref.c | 15 +-
> fs/btrfs/delayed-ref.h | 11 --
> fs/btrfs/disk-io.c | 2 +
> fs/btrfs/extent-tree.c | 3 -
> fs/btrfs/qgroup.c | 339 +++++++++++++++++++++++++++--------
> fs/btrfs/qgroup.h | 120 +++++++++++--
> fs/btrfs/relocation.c | 101 ++++++++---
> fs/btrfs/transaction.c | 1 +
> include/trace/events/btrfs.h | 29 ---
> 12 files changed, 502 insertions(+), 172 deletions(-)
>
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