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. I'll try to fix it soon. Thanks, Qu > > Thanks, > Misono > >
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