How exclusive in parent qgroup is computed? (was: Re: exclusive subvolume space missing)

[Andrei Borzenkov <arvidjaar@gmail.com>]

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02.12.2017 03:27, Qu Wenruo пишет:
> 
> That's the difference between how sub show and quota works.
> 
> For quota, it's per-root owner check.
> Means even a file extent is shared between different inodes, if all
> inodes are inside the same subvolume, it's counted as exclusive.
> And if any of the file extent belongs to other subvolume, then it's
> counted as shared.
> 

Could you also explain how parent qgroup computes exclusive space? I.e.

10:~ # mkfs -t btrfs -f /dev/sdb1
btrfs-progs v4.13.3
See http://btrfs.wiki.kernel.org for more information.

Performing full device TRIM /dev/sdb1 (1023.00MiB) ...
Label:              (null)
UUID:               b9b0643f-a248-4667-9e69-acf5baaef05b
Node size:          16384
Sector size:        4096
Filesystem size:    1023.00MiB
Block group profiles:
  Data:             single            8.00MiB
  Metadata:         DUP              51.12MiB
  System:           DUP               8.00MiB
SSD detected:       no
Incompat features:  extref, skinny-metadata
Number of devices:  1
Devices:
   ID        SIZE  PATH
    1  1023.00MiB  /dev/sdb1

10:~ # mount -t btrfs /dev/sdb1 /mnt
10:~ # cd /mnt
10:/mnt # btrfs quota enable .
10:/mnt # btrfs su cre sub1
Create subvolume './sub1'
10:/mnt # dd if=/dev/urandom of=sub1/file1 bs=1K count=1024
1024+0 records in
1024+0 records out
1048576 bytes (1.0 MB, 1.0 MiB) copied, 0.00833739 s, 126 MB/s
10:/mnt # dd if=/dev/urandom of=sub1/file2 bs=1K count=1024
1024+0 records in
1024+0 records out
1048576 bytes (1.0 MB, 1.0 MiB) copied, 0.0179272 s, 58.5 MB/s
10:/mnt # btrfs subvolume snapshot sub1 sub2
Create a snapshot of 'sub1' in './sub2'
10:/mnt # dd if=/dev/urandom of=sub2/file2 bs=1K count=1024 conv=notrunc
1024+0 records in
1024+0 records out
1048576 bytes (1.0 MB, 1.0 MiB) copied, 0.0348762 s, 30.1 MB/s
10:/mnt # btrfs qgroup show --sync -p .
qgroupid         rfer         excl parent
--------         ----         ---- ------
0/5          16.00KiB     16.00KiB ---
0/256         2.02MiB      1.02MiB ---
0/257         2.02MiB      1.02MiB ---

So far so good. This is expected, each subvolume has 1MiB shared and
1MiB exclusive.

10:/mnt # btrfs qgroup create 22/7 /mnt
10:/mnt # btrfs qgroup assign --rescan 0/256 22/7 /mnt
Quota data changed, rescan scheduled
10:/mnt # btrfs quota rescan -s /mnt
no rescan operation in progress
10:/mnt # btrfs qgroup assign --rescan 0/257 22/7 /mnt
Quota data changed, rescan scheduled
10:/mnt # btrfs quota rescan -s /mnt
no rescan operation in progress
10:/mnt # btrfs qgroup show --sync -p .
qgroupid         rfer         excl parent
--------         ----         ---- ------
0/5          16.00KiB     16.00KiB ---
0/256         2.02MiB      1.02MiB 22/7
0/257         2.02MiB      1.02MiB 22/7
22/7          3.03MiB      3.03MiB ---
10:/mnt #

Oops. Total for 22/7 is correct (1MiB shared + 2 * 1MiB exclusive) but
why all data is treated as exclusive here? It does not match your
explanation ...


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