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

[Satoru Takeuchi <takeuchi_satoru@jp.fujitsu.com>]

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?

* 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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