maxpct option for small xfs filesystems

[Alexander Tsvetkov]

On 01/27/2015 07:31 PM, Eric Sandeen wrote:
> On 1/27/15 10:23 AM, Alexander Tsvetkov wrote:
>
> ...
>
>> I have not the same results,  just installed 3.19-rc6 and repeated the test.,
>> df -i reports 640 inodes for filesystem, but actually created 40512 files:
>>
>> [root at fedora ~]# mkfs.xfs -f -d size=16m -i maxpct=1 /dev/sdb2
>> meta-data=/dev/sdb2              isize=256    agcount=1, agsize=4096 blks
>>           =                       sectsz=512   attr=2, projid32bit=1
>>           =                       crc=0        finobt=0
>> data     =                       bsize=4096   blocks=4096, imaxpct=1
>>           =                       sunit=0      swidth=0 blks
>> naming   =version 2              bsize=4096   ascii-ci=0 ftype=0
>> log      =internal log           bsize=4096   blocks=853, version=2
>>           =                       sectsz=512   sunit=0 blks, lazy-count=1
>> realtime =none                   extsz=4096   blocks=0, rtextents=0
>> [root at fedora ~]# mount /dev/sdb2 /mnt/scratch/
>> fill with files until enospc...
>> [root at fedora ~]# df -i /mnt/scratch/
>> Filesystem     Inodes IUsed IFree IUse% Mounted on
>> /dev/sdb2         640   640     0  100% /mnt/scratch
>> [root at fedora ~]# df -Th /mnt/scratch/
>> Filesystem     Type  Size  Used Avail Use% Mounted on
>> /dev/sdb2      xfs    13M   13M  156K  99% /mnt/scratch
>> [root at fedora ~]# umount /mnt/scratch
>> [root at fedora ~]# xfs_db -c "blockget -n" -c "ncheck" /dev/sdb2 | wc -l
>> 40512
> and what does df -i say after remount?
Nothing changed after remount:

[root at fedora ~]# xfs_db -c "blockget -n" -c "ncheck" /dev/sdb2 | wc -l
40512
[root at fedora ~]# mount /dev/sdb2 /mnt/scratch/
[root at fedora ~]# xfs_info /mnt/scratch/
meta-data=/dev/sdb2 isize=256 agcount=1, agsize=4096 blks
                  =                sectsz=512   attr=2, projid32bit=1
                  =                crc=0 finobt=0
data          =                bsize=4096   blocks=4096, imaxpct=1
                  =                sunit=0      swidth=0 blks
naming     =version 2 bsize=4096   ascii-ci=0 ftype=0
log            =internal    bsize=4096   blocks=853, version=2
                  =                sectsz=512   sunit=0 blks, lazy-count=1
realtime    =none        extsz=4096   blocks=0, rtextents=0
[root at fedora ~]# df -i /mnt/scratch/
Filesystem     Inodes IUsed IFree IUse% Mounted on
/dev/sdb2         640   640     0  100% /mnt/scratch
[root at fedora ~]# umount /mnt/scratch
[root at fedora ~]# xfs_db -c "blockget -n" -c "ncheck" /dev/sdb2 | wc -l
40512
[root at fedora ~]# mount /dev/sdb2 /mnt/scratch/
[root at fedora ~]# df -i /mnt/scratch/
Filesystem     Inodes IUsed IFree IUse% Mounted on
/dev/sdb2         640   640     0  100% /mnt/scratch
[root at fedora ~]# mount -o remount /dev/sdb2 /mnt/scratch/
[root at fedora ~]# df -i /mnt/scratch/
Filesystem     Inodes IUsed IFree IUse% Mounted on
/dev/sdb2         640   640     0  100% /mnt/scratch
[root at fedora ~]# umount /mnt/scratch
[root at fedora ~]# xfs_db -c "blockget -n" -c "ncheck" /dev/sdb2 | wc -l
40512

>
> This is actually a problem with the lazy superblock counters I've run into before,
> but haven't yet fixed.  This kind of workload is such that it never trips the
> runtime rebalancing.
>
>> Looking into ncheck output there are 40512 pairs reported in the output each with own unique
>> inode number. ncheck doesn't report inodes count by definition, but what does these
>> 40512 reported inode numbers mean if only actually 640 inodes were allocated? From another hand
>> each new file should have associated meta-data in the corresponding allocated inode structure, so for
>> 40512 newly created files I expect the same count of allocated inodes, is it correct?
> Recheck df -i after remount, I think you will see many more than 640.
Do you mean that ncheck reports right number of allocated inodes instead 
of df -i? If counters are incorrect then the
maxpct limit is not working as well, because there are much more of 
filesystem space allocated for inodes then defined limit 1%.

What is expected behaviour in this case when it's required for fs to 
allocate new inodes starting to exceed defined maxpct
percentage? Which error is expected to be returned to user, enospc or 
probably just some warning?


>
> -Eric
Thanks,
Alexander Tsvetkov