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Re: maxpct option for small xfs filesystems

To: Alexander Tsvetkov <alexander.tsvetkov@xxxxxxxxxx>, Dave Chinner <david@xxxxxxxxxxxxx>
Subject: Re: maxpct option for small xfs filesystems
From: Eric Sandeen <sandeen@xxxxxxxxxxx>
Date: Tue, 27 Jan 2015 10:31:28 -0600
Cc: xfs@xxxxxxxxxxx
Delivered-to: xfs@xxxxxxxxxxx
In-reply-to: <54C7BB78.4060203@xxxxxxxxxx>
References: <54C667F3.8040303@xxxxxxxxxx> <20150126223715.GA7621@dastard> <54C7BB78.4060203@xxxxxxxxxx>
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@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@fedora ~]# mount /dev/sdb2 /mnt/scratch/
> fill with files until enospc...
> [root@fedora ~]# df -i /mnt/scratch/
> Filesystem     Inodes IUsed IFree IUse% Mounted on
> /dev/sdb2         640   640     0  100% /mnt/scratch
> [root@fedora ~]# df -Th /mnt/scratch/
> Filesystem     Type  Size  Used Avail Use% Mounted on
> /dev/sdb2      xfs    13M   13M  156K  99% /mnt/scratch
> [root@fedora ~]# umount /mnt/scratch
> [root@fedora ~]# xfs_db -c "blockget -n" -c "ncheck" /dev/sdb2 | wc -l
> 40512

and what does df -i say after remount?

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.

-Eric

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