[PVE-User] PBS : is dirty-bitmap really accurate ?

Jorge Boncompte jbonor at gmail.com
Thu Jul 23 11:00:55 CEST 2020


El 23/7/20 a las 8:53, Daniel Berteaud escribió:
> ----- Le 23 Juil 20, à 8:43, Fabian Grünbichler f.gruenbichler at proxmox.com a écrit :
> 
>> possibly you haven't upgraded to pve-qemu-kvm 5.0-11 (or your VM hasn't
>> been restarted yet since the upgrade):
>>
>> https://git.proxmox.com/?p=pve-qemu.git;a=commit;h=f257cc05f4fbf772cad3231021b3ce7587127a1b
> 
> I'm running pve-qemu-kvm 5.0.0-11, and all the implied VM have been either (cold) rebooted, or migrated.
> 
>>
>> the bitmap has a granularity of 4MB, so depending on the activity inside
>> you can see quite a bit of amplification. also writing and then
>> zeroing/reverting again to the old content would leave a mark in the
>> bitmap without permanently changing the contents.
>>
> 
> Yes, I'd expect some amplification, but not that much. For my Zabbix server, it's nearly canceling all the benefit of using a dirty bitmap.
> One thing I've noted, is that I get expected values at least for one guest, running PfSense (where I get ~150MB of dirty blocks each days). Most of my other VM are Linux, I'll check if it could be related to the atime update or something

	Hi, does the dirty-bitmap take somehow into account block discarding
and zeroing? Because the other thing I would look for in this case is
for a fstrim firing every day.

> 
> Cheers,
> Daniel
> 




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