System freeze for few seconds when using dm-cache on high load

System freeze for few seconds when using dm-cache on high load

[Michał Zubkowicz]

I'm using dm-cache on such setup:
dm-cache -> luks -> lvm2 ->ext4
Kernel version: 3.13.0-43

On high disk load (ie when saving virtual machine state) whole system 
freezes for a few seconds.
I've tried already to change scheduler (from deadline to cbq), change 
ext4 mount options, now i've got:
errors=remount-ro,noatime,nodiratime,discard,barrier=0,relatime

There is something I should check, or maybe it's a 'normal' behaviour, 
or maybe my  whole setup is wrong?

-- 
Best Regards
Michał Zubkowicz

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Re: System freeze for few seconds when using dm-cache on high load

[Anssi Hannula]

Hi,

14.01.2015, 14:34, Michał Zubkowicz kirjoitti:
> I'm using dm-cache on such setup:
> dm-cache -> luks -> lvm2 ->ext4
> Kernel version: 3.13.0-43
> 
> On high disk load (ie when saving virtual machine state) whole system 
> freezes for a few seconds.
> I've tried already to change scheduler (from deadline to cbq), change 
> ext4 mount options, now i've got:
> errors=remount-ro,noatime,nodiratime,discard,barrier=0,relatime
> 
> There is something I should check, or maybe it's a 'normal' behaviour, 
> or maybe my  whole setup is wrong?
> 

Can't really help you directly, but just for the record, I also get
whole-system (i.e. not just frozen disks) freezes of 10-60 seconds on
heavy disk load on a somewhat similar system:
kernel 3.14.27,
md-raid6 (16x 4TB) -> lvm with lvm-cache (dm-cache) -> luks -> ext4.

Haven't had the time to investigate further, and they are still rather
rare for me (~1 per month).
They seemed to start when I added dm-cache and luks to the setup.

No messages appear in kernel log when it happens.


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Anssi Hannula

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