Bug 110111 - btrfs fi usage reports bogus 16EiB free space
Summary: btrfs fi usage reports bogus 16EiB free space
Status: RESOLVED CODE_FIX
Alias: None
Product: File System
Classification: Unclassified
Component: btrfs (show other bugs)
Hardware: All Linux
: P1 normal
Assignee: Josef Bacik
URL:
Keywords:
Depends on:
Blocks:
 
Reported: 2015-12-29 00:04 UTC by Chris Murphy
Modified: 2016-01-13 15:42 UTC (History)
1 user (show)

See Also:
Kernel Version: 4.4.0-0.rc6.git0.1.fc24.x86_64
Subsystem:
Regression: No
Bisected commit-id:

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Description Chris Murphy 2015-12-29 00:04:43 UTC 
btrfs-progs-4.3.1-1.fc23.x86_64

1. Used f3write to test a USB stick formatted with mkfs.btrfs -M, this fills the entire device.
2. btrfs fi usage <mp>

Actual results:

[root@f23m ~]# btrfs fi usage /mnt/king
WARNING: MIXED blockgroups not handled
Overall:
    Device size:		  14.91GiB
    Device allocated:		  29.82GiB
    Device unallocated:		  16.00EiB
    Device missing:		     0.00B
    Used:			  29.23GiB
    Free (estimated):		  16.00EiB	(min: 16.00EiB)    !!!!!!!
    Data ratio:			      1.00
    Metadata ratio:		      1.00
    Global reserve:		 300.00MiB	(used: 0.00B)

Data+Metadata,single: Size:14.91GiB, Used:14.62GiB
   /dev/sdd	  14.91GiB

System,single: Size:4.00MiB, Used:4.00KiB
   /dev/sdd	   4.00MiB

Unallocated:
   /dev/sdd	     0.00B

[root@f23m ~]# df -h
Filesystem      Size  Used Avail Use% Mounted on
[..snip...]
/dev/sdd         15G   15G  301M  99% /mnt/king

[root@f23m ~]# btrfs fi df /mnt/king/
System, single: total=4.00MiB, used=4.00KiB
Data+Metadata, single: total=14.91GiB, used=14.62GiB
GlobalReserve, single: total=300.00MiB, used=0.00B

[root@f23m ~]# btrfs fi show /mnt/king
Label: none  uuid: 8040969d-6809-4c7a-9126-afbbb127a719
	Total devices 1 FS bytes used 14.62GiB
	devid    1 size 14.91GiB used 14.91GiB path /dev/sdd



Expected:

Should report in the vicinity of 300MiB free, not 16.00EiB.
Comment 1 Chris Murphy 2015-12-29 02:51:08 UTC 
Regression testing.

With a new mkfs, and mounting the new empty fs, I get this:

[root@f23m ~]# btrfs fi usage /mnt/king
WARNING: MIXED blockgroups not handled
Overall:
    Device size:		  14.91GiB
    Device allocated:		  20.00MiB
    Device unallocated:		  14.89GiB
    Device missing:		     0.00B
    Used:			  60.00KiB
    Free (estimated):		  14.90GiB	(min: 14.90GiB)
    Data ratio:			      1.00
    Metadata ratio:		      1.00
    Global reserve:		   4.00MiB	(used: 0.00B)

Data+Metadata,single: Size:8.00MiB, Used:28.00KiB
   /dev/sdd	   8.00MiB

System,single: Size:4.00MiB, Used:4.00KiB
   /dev/sdd	   4.00MiB

Unallocated:
   /dev/sdd	  14.90GiB


And then after copying ~837MiB file, the problem still doesn't happen.


[root@f23m ~]# btrfs fi usage /mnt/king/
WARNING: MIXED blockgroups not handled
Overall:
    Device size:		  14.91GiB
    Device allocated:		   2.02GiB
    Device unallocated:		  12.89GiB
    Device missing:		     0.00B
    Used:			   1.64GiB
    Free (estimated):		  13.08GiB	(min: 13.08GiB)
    Data ratio:			      1.00
    Metadata ratio:		      1.00
    Global reserve:		  20.00MiB	(used: 0.00B)

Data+Metadata,single: Size:1.01GiB, Used:837.86MiB
   /dev/sdd	   1.01GiB

System,single: Size:4.00MiB, Used:4.00KiB
   /dev/sdd	   4.00MiB

Unallocated:
   /dev/sdd	  13.90GiB


However, the Used amount is off by a factor of 2x.

[root@f23m king]# btrfs fi df /mnt/king/
System, single: total=4.00MiB, used=4.00KiB
Data+Metadata, single: total=1.01GiB, used=837.86MiB
GlobalReserve, single: total=20.00MiB, used=0.00B


Around 48% used (per conventional df, which matches up reasonably well with btrfs fi df), "fi usage" flips from a sane looking (but still wrong) value to 16.00EiB.

This may be due to the lack of support for mixedbg by 'fi usage'.
Comment 2 David Sterba 2016-01-13 15:42:56 UTC 
Mixed block groups reporting in 'fi usage' should be fixed in devel, queued for 4.4.
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