Re: Filesystem wedges caused by r251446

From: Konstantin Belousov <kostikbel_at_gmail.com>
Date: Sat, 13 Jul 2013 13:03:37 +0300
On Sat, Jul 13, 2013 at 10:14:06AM +0200, Ian FREISLICH wrote:
> Konstantin Belousov wrote:
> > On Fri, Jul 12, 2013 at 11:34:18PM +0200, Ian FREISLICH wrote:
> > > (kgdb) print runningbufreq
> > > $1 = 1
> > > (kgdb) print runningbufspace
> > > $2 = 0
> > > (kgdb) print lorunningspace
> > > $3 = 4587520
> > > (kgdb) print hirunningspace
> > > $4 = 4194304
> > 
> > This is extremely weird.  The hirunningspace is less then lorunningspace,
> > am I right ?  This causes the runningbufspace machinery to never wake up
> 
> Yes.  This state of affairs doesn't happen on r251445 and further
> testing on my side shows it doesn't hapen on all my amd64 servers.
> It appears that this particular server type (Dell R200) running
> amd64 with geom_mirror is affected.  I will have to test further
> by destroying the mirror and removing it from the kernel and see
> if I can still reproduce the issue.  Perhaps r251446 exposes
> insufficient locking on opperations affecting these variables.
No.  The lorunningspace is constant for the system lifetime.
It can only be changed by the sysctl vfs.lorunningspace.
Look into /etc/sysctl.conf or scripts which apply sysctl settings.

Boot the system single-user and show the
sysctl vfs.lorunningspace
sysctl vfs.hirunningspace

Compare the values from single user with the values after the system
booted normal.

> 
> > I just verified on the 4G VM on amd64, my numbers for lo is 4587520,
> > for high 6881280.  Verify your tuning and kernel options, which you should
> > have provided with the original report, I think.
> 
> Sorry about that (and I'm relieved:) I had originally compiled with
> CPUTYPE?=opteron which is incorrect for this CPU.  However the
> problem persists with CPUTYPE?=core2, but I'm not sure how much of
> a difference this makes with clang.  Also, I have another affected
> host that's compiled with gcc and the correct CPUTYPE so I doubt
> it's the compiler.
> 
This is irrelevant, CPU type cannot affect the calculation, unless the
compiler is horribly broken.

Received on Sat Jul 13 2013 - 08:03:44 UTC

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