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Re: Enabling quota on XFS filesystem with many files hangs

To: Dave Chinner <david@xxxxxxxxxxxxx>
Subject: Re: Enabling quota on XFS filesystem with many files hangs
From: Milan Holzäpfel <listen@xxxxxxxx>
Date: Tue, 13 Nov 2012 16:23:56 +0100
Cc: xfs@xxxxxxxxxxx
In-reply-to: <20121028215713.GM29378@dastard>
References: <20121026191540.ca9ee64db2a51e7166b7fadc@xxxxxxxx> <508ADE1C.40208@xxxxxxxxxxx> <20121028132050.c8d143729cd565307fcee279@xxxxxxxx> <20121028215713.GM29378@dastard>
On Mon, 29 Oct 2012 08:57:13 +1100
Dave Chinner <david@xxxxxxxxxxxxx> wrote:

> On Sun, Oct 28, 2012 at 01:20:50PM +0100, Milan Holzäpfel wrote:
> > On Fri, 26 Oct 2012 14:01:48 -0500
> > Eric Sandeen <sandeen@xxxxxxxxxxx> wrote:
> > 
> > > On 10/26/12 12:15 PM, Milan Holzäpfel wrote:
> > > > Hello all, 
> > > > 
> > > > I have an XFS filesystem of size 1.2 TiB with 101 GiB free space and 14
> > > > million inodes in use. 
> > 
> > Meanwhile, I deleted 200 GiB of data on that filesystem, with 9.9
> > million inodes still in use. Now, quotacheck just works. 
> IOWs, the problem is load related.

I'm not quite sure what you mean by "load". During the quotacheck, the
quotacheck was almost the sole source of I/O. I only started programs
like "top", "iotop", "smartctl -a" or "hddtemp" during the quotacheck. 

> And slow SATA drives will not improve the situation, either.  The
> software RAID with small random writes that quotacheck does will
> cause lots of RMW cycles and hence be very slow. This, alone, can
> trigger hung task warnings. When you add encryption to the stack,
> the storage stack will be even slower.
> If you can reproduce it, I'd be really interested to know what the
> sysrq-w output shows, as it will probably indicate a dm-crypt or md
> thread hung waiting for something else to occur....

I tried to reproduce it, but didn't succeed. I moved a copy of the
original 200 GiB of data on the filesystem, I created lot's of new,
small files until the FS had 17 M used inodes and 84 GiB free space,
but quotacheck finished normally. 

I really don't understand why it has disappeared: As far as I remember,
I made two attempts to run quotacheck before removing the 200 GiB, and
it hung both times.  Nothing in the system setup has changed. 
Anyway, the problem doesn't seem to exist anymore. 

Thanks for your interest. 

Milan Holzäpfel

Milan Holzäpfel <listen@xxxxxxxx>

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