Hi Qu,
Hi Chris,
Please pull the 19 patchset from my branch for_chris_4.2.
We have tested it in a week.
Although it is originally based on 4.1-rc5, not the integration branch.
Quick tests shows no new bugs, although we will rerun the full test,
I'll send the patchset first for your reviewing:
https://github.com/adam900710/linux.git for_chris_4.2
This contains the following patches.
1. Qgroup rework (first 18 commits)
These commits rework the qgroup framework.
Now, quota won't need to do per-delayed-ref accounting.
But only need to record dirty delayed-ref, and account quota at transaction time.
Can you share perfomaces results with/without patches with quota enabled.
Especially, if there are thounds of snapshots, how much performaces down or up
with these patches applied.
Regards,
Wang Shilong
For multi-snapshot case, the test is still running and I'll post the
result ASAP.
But we already have the performance(sysbench) result between quota
disabled and quota enabled with the pull.
Note: we have already done tests on the pull branch, and it shows no
performance regression compared to 4.1-rc5 without quota.
So the result without quota should be a correct baseline.
Overall, the performance drop is below 5% and I think it's completely
acceptable for the complex of btrfs quota compared to other filesystems.
Only one tests shows a performance drop over 5%:
1. Random read with DIO on small files, single thread, 4K block size.
The drop is about 11%.
And some result may not be stable enough, we will double check but it
needs a lot of time to do performance test.
For the full result, please refer to the google docs URL:
https://docs.google.com/spreadsheets/d/1m5c96PrxigtLl_m5OlMdrTUxr82CxJuOGDbjtDrv_I8/edit?usp=sharing
Thanks,
Qu
The good thing is, at transaction time, we have no other interruption or
concurrency, account can be quite accurate and only need to account once
for every dirty extent.(especially faster for shared extents)
And clearer codes and logic. Codes changes from 1K to 0.5K, even a lot
of comments are added.
With the patchset, btrfs can pass all qgroup test in fstests.
No longer minus number now.
The only problem left is, we need a new mechanism to account subvolume deletion. But this is the long-existing problem, I'd prefer to address
it in next merge windows if we have a pretty method to solve it.
Or maybe a small patch to mark qgroup inconsistent when delete subvolume with level higher than 0.
2. write-rm-loop fixes from Zhao Lei.
Other patches from Zhao Lei and Forrest Liu have already been merged
into mainline, but this is the one still unmerged.
This patch fixes the last super rare problem we found in write-rm-loop
case.
And the patch will only modify the minor routine, so it won't affect the normal routine.
Thanks,
Qu
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