On 8/8/18 3:48 PM, Qu Wenruo wrote:
>
>
> On 2018年08月08日 15:41, Misono Tomohiro wrote:
>> On 2018/08/08 15:04, Qu Wenruo wrote:
>>> When quota is enabled and we do a snapshot, we just update the 'excl'
>>> number of both snapshot src and dst to src's 'rfer' - nodesize.
>>>
>>> It's a quick hack to avoid quota rescan every time we create a snapshot
>>> and it works if src doesn't belong to other qgroups.
>>>
>>> But if we have higher level qgroups, such behavior only works for level
>>> 0 qgroups, and higher level qgroups don't get update, thus making qgroup
>>> number inconsistent.
>>>
>>> The problem of updating higher level qgroup numbers is, it's way to
>>> complex.
>>>
>>> Under the following case, it's pretty simple: (src is 257, dst is 258)
>>> 0/257 - 1/0, 0/258.
>>>
>>> In this case, we only need to modify 1/0 to reduce its 'excl'
>>>
>>> But under the following case, it will go out of control:
>>>
>>> 0/257 - 1/0, 0/258 - 1/1 (using -i option), 1/0 - 2/0, 1/1 - 2/0.
>>>
>>> So to make it simple, if snapshot src has higher level qgroups, just
>>> mark qgroup inconsistent and let later rescan to do its job.
>>>
>>> Reported-by: Misono Tomohiro <misono.tomoh...@jp.fujitsu.com>
>>> Signed-off-by: Qu Wenruo <w...@suse.com>
>>> ---
>>> fs/btrfs/qgroup.c | 16 ++++++++++++++++
>>> 1 file changed, 16 insertions(+)
>>>
>>> diff --git a/fs/btrfs/qgroup.c b/fs/btrfs/qgroup.c
>>> index ec4351fd7537..2b3d2dd1b735 100644
>>> --- a/fs/btrfs/qgroup.c
>>> +++ b/fs/btrfs/qgroup.c
>>> @@ -2298,6 +2298,22 @@ int btrfs_qgroup_inherit(struct btrfs_trans_handle
>>> *trans,
>>> if (!srcgroup)
>>> goto unlock;
>>>
>>> + /*
>>> + * If snapshot source is belonging to high level qgroups, it
>>> + * will be a more complex to hack the numbers.
>>> + * E.g. source is 257, snapshot is 258:
>>> + * 0/257 - 1/0, creating snapshot 258 will need to update 1/0
>>> + * It's too complex when higher level qgroup is involved.
>>> + * Mark qgroup inconsistent for later rescan
>>> + */
>>> + if (!list_empty(&srcgroup->groups)) {
>>> + btrfs_info_rl(fs_info,
>>> +"src qgroup 0/%llu belongs to higher level qgroup, creating snapshot for
>>> it need qgroup rescan",
>>> + srcid);
>>> + fs_info->qgroup_flags |=
>>> + BTRFS_QGROUP_STATUS_FLAG_INCONSISTENT;
>>> + goto unlock;
>>> + }
>>> /*
>>> * We call inherit after we clone the root in order to make sure
>>> * our counts don't go crazy, so at this point the only
>>>
>>
>> Thanks for the quick fix.
>> Tested-by/Reviewed-by: Misono Tomohiro <misono.tomoh...@jp.fujitsu.com>
>>
>> However there is still another problem about removing relation:
>>
>> (4.18-rc7 with above patch)
>> $ mkfs.btrfs -fq $DEV
>> $ mount $DEV /mnt
>>
>> $ btrfs quota enable /mnt
>> $ btrfs qgroup create 1/0 /mnt
>> $ btrfs sub create /mnt/sub
>> $ btrfs qgroup assign 0/257 1/0 /mnt
>>
>> $ dd if=/dev/urandom of=/mnt/sub/file bs=1k count=1000
>> $ btrfs sub snap /mnt/sub /mnt/snap
>> $ dmesg | tail -n 1
>> BTRFS info (device sdb7): src qgroup 0/257 belongs to higher level qgroup,
>> creating snapshot for it need qgroup rescan
>>
>> $ btrfs quota rescan -w /mnt
>> $ btrfs qgroup show -pcre /mnt
>> qgroupid rfer excl max_rfer max_excl parent child
>> -------- ---- ---- -------- -------- ------ -----
>> 0/5 16.00KiB 16.00KiB none none --- ---
>> 0/257 1016.00KiB 16.00KiB none none 1/0 ---
>> 0/258 1016.00KiB 16.00KiB none none --- ---
>> 1/0 1016.00KiB 16.00KiB none none --- 0/257
>>
>> so far so good, but:
>>
>> $ btrfs qgroup remove 0/257 1/0 /mnt
>> WARNING: quotas may be inconsistent, rescan needed
>> $ btrfs quota rescan -w /mnt
>> $ btrfs qgroup show -pcre /mnt
>> qgoupid rfer excl max_rfer max_excl parent child
>> -------- ---- ---- -------- -------- ------ -----
>> 0/5 16.00KiB 16.00KiB none none --- ---
>> 0/257 1016.00KiB 16.00KiB none none --- ---
>> 0/258 1016.00KiB 16.00KiB none none --- ---
>> 1/0 1016.00KiB 16.00KiB none none --- ---
>> ^^^^^^^^^^ ^^^^^^^^ not cleared
>>
>> It seems some fix is needed for rescan too.
>
> In this particular case, it's not hard to fix.
>
> In fact for deleting/assigning qgroup with rfer == excl case, it should
> go through the quick accounting path.
>
> But it looks like remove path doesn't go that path.My fault, in this case, since rfer != excl, so we can't go quick updating. But on the other hand, if you don't remove the 0 level qgroup 0/257 directly, but using subvolume delete, qgroup should update 0/257 to rfer = 0 and excl = 0, and then remove qgroup relationship should work without the need to rescan. Thanks, Qu > > I'll try to fix it soon. > > Thanks, > Qu > >> >> Thanks, >> Misono >> >> >
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