Re: [PATCH] btrfs: get the accurate value of used_bytes in btrfs_get_block_group_info().

[Dongsheng Yang <yangds.fnst@cn.fujitsu.com>]

On 01/07/2015 05:22 PM, Qu Wenruo wrote:
> Hi Satoru-san
>> Hi Dongsheng,
>>
>> On 2015/01/05 20:19, Dongsheng Yang wrote:
>>
>>> Ping.....
>>>
>>> IOCTL of BTRFS_IOC_SPACE_INFO currently does not report
>>> the data used but not synced to user.  Then btrfs fi df will
>>> give user a wrong numbers before sync. This patch solve
>>> this problem.
>>>
>>> On 10/27/2014 08:38 PM, Dongsheng Yang wrote:
>>>> Reproducer:
>>>>     # mkfs.btrfs -f -b 20G /dev/sdb
>>>>     # mount /dev/sdb /mnt/test
>>>>     # fallocate  -l 17G /mnt/test/largefile
>>>>     # btrfs fi df /mnt/test
>>>>     Data, single: total=17.49GiB, used=6.00GiB <- only 6G, but 
>>>> actually it should be 17G.
>>>>     System, DUP: total=8.00MiB, used=16.00KiB
>>>>     System, single: total=4.00MiB, used=0.00B
>>>>     Metadata, DUP: total=1.00GiB, used=112.00KiB
>>>>     Metadata, single: total=8.00MiB, used=0.00B
>>>>     GlobalReserve, single: total=16.00MiB, used=0.00B
>>
>> I tried to reproduce your problem with 3.19-rc1.
>> However, this problem doesn't happen. Could you
>> also try to reproduce with the upstream kernel?
> I can still reproduce it in 3.18, but it seems to be fixed in 3.19-rc1 
> already by other patch,
> so this patch is no longer needed.

Oops, my fault. I forgot to test it with upstream. :(

Satoru and Qu, thanx a lot.

Yang
>
> Thanks,
> Qu
>>
>> * Detail
>>
>> test script (named "yang-test.sh" here):
>> =============================================================================== 
>>
>> #!/bin/bash -x
>>
>> PART1=/dev/vdb
>> MNT_PNT=./mnt
>> mkfs.btrfs -f -b 20G ${PART1}
>> mount ${PART1} ${MNT_PNT}
>> fallocate -l 17G ${MNT_PNT}/largefile
>> btrfs fi df ${MNT_PNT}
>> sync
>> btrfs fi df ${MNT_PNT}
>> umount ${MNT_PNT}
>> =============================================================================== 
>>
>>
>> Result:
>> =============================================================================== 
>>
>> # ./yang-test.sh
>> + PART1=/dev/vdb
>> + MNT_PNT=./mnt
>> + mkfs.btrfs -f -b 20G /dev/vdb
>> Btrfs v3.17
>> See http://btrfs.wiki.kernel.org for more information.
>>
>> Turning ON incompat feature 'extref': increased hardlink limit per 
>> file to 65536
>> fs created label (null) on /dev/vdb
>>         nodesize 16384 leafsize 16384 sectorsize 4096 size 20.00GiB
>> + mount /dev/vdb ./mnt
>> + fallocate -l 17G ./mnt/largefile
>> + btrfs fi df ./mnt
>> Data, single: total=17.01GiB, used=17.00GiB   # Used 17GiB properly
>> System, DUP: total=8.00MiB, used=16.00KiB
>> System, single: total=4.00MiB, used=0.00B
>> Metadata, DUP: total=1.00GiB, used=112.00KiB
>> Metadata, single: total=8.00MiB, used=0.00B
>> GlobalReserve, single: total=16.00MiB, used=0.00B
>> + sync
>> + btrfs fi df ./mnt
>> Data, single: total=17.01GiB, used=17.00GiB    # (of course) used 
>> 17GiB too
>> System, DUP: total=8.00MiB, used=16.00KiB
>> System, single: total=4.00MiB, used=0.00B
>> Metadata, DUP: total=1.00GiB, used=112.00KiB
>> Metadata, single: total=8.00MiB, used=0.00B
>> GlobalReserve, single: total=16.00MiB, used=0.00B
>> + umount ./mnt
>> =============================================================================== 
>>
>>
>> Although I ran this test five times, the results are the same.
>>
>> Thanks,
>> Satoru
>>
>>>>     # sync
>>>>     # btrfs fi df /mnt/test
>>>>     Data, single: total=17.49GiB, used=17.00GiB <- After sync, it 
>>>> is expected.
>>>>     System, DUP: total=8.00MiB, used=16.00KiB
>>>>     System, single: total=4.00MiB, used=0.00B
>>>>     Metadata, DUP: total=1.00GiB, used=112.00KiB
>>>>     Metadata, single: total=8.00MiB, used=0.00B
>>>>     GlobalReserve, single: total=16.00MiB, used=0.00B
>>>>
>>>> The value of 6.00GiB is actually calculated in 
>>>> btrfs_get_block_group_info()
>>>> by adding the @block_group->item->used for each group together. In 
>>>> this way,
>>>> it did not consider the bytes in cache.
>>>>
>>>> This patch adds the value of @pinned, @reserved and @bytes_super in
>>>> struct btrfs_block_group_cache to make sure we can get the accurate 
>>>> @used_bytes.
>>>>
>>>> Reported-by: Qu Wenruo <quwenruo@cn.fujitsu.com>
>>>> Signed-off-by: Dongsheng Yang <yangds.fnst@cn.fujitsu.com>
>>>> ---
>>>>   fs/btrfs/ioctl.c | 4 ++++
>>>>   1 file changed, 4 insertions(+)
>>>>
>>>> diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
>>>> index 33c80f5..bc2aaeb 100644
>>>> --- a/fs/btrfs/ioctl.c
>>>> +++ b/fs/btrfs/ioctl.c
>>>> @@ -3892,6 +3892,10 @@ void btrfs_get_block_group_info(struct 
>>>> list_head *groups_list,
>>>>           space->total_bytes += block_group->key.offset;
>>>>           space->used_bytes +=
>>>> btrfs_block_group_used(&block_group->item);
>>>> +        /* Add bytes-info in cache */
>>>> +        space->used_bytes += block_group->pinned;
>>>> +        space->used_bytes += block_group->reserved;
>>>> +        space->used_bytes += block_group->bytes_super;
>>>>       }
>>>>   }
>>>
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> .
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