[pve-devel] disabling transparent hugepage by default like kernel 2.6.32 ?

[Alexandre DERUMIER]

here an interesting recent lklm discussion about THP

http://www.spinics.net/lists/linux-mm/msg84776.html

----- Mail original -----
De: "aderumier" <aderumier at odiso.com>
À: "Andreas Steinel" <a.steinel at gmail.com>
Cc: "pve-devel" <pve-devel at pve.proxmox.com>
Envoyé: Mercredi 9 Septembre 2015 17:43:58
Objet: Re: [pve-devel] disabling transparent hugepage by default like kernel 2.6.32 ?

>>In my benchmarks, THP increase the memory transaction speed by 5-10% in the KVM guest if THP is activated on the host side, not in the VM side. I know that THP for databases is bad, but we are not using THP in the guest >>where the database lives. Can someone provide some benchmarks for that case or further information? Any suggestions? 

Oh, good to known. 

How much memory do you use it your vm ? what is the database software ? 

----- Mail original ----- 
De: "Andreas Steinel" <a.steinel at gmail.com> 
À: "Daniel Hunsaker" <danhunsaker at gmail.com> 
Cc: "aderumier" <aderumier at odiso.com>, "dietmar" <dietmar at proxmox.com>, "pve-devel" <pve-devel at pve.proxmox.com> 
Envoyé: Mercredi 9 Septembre 2015 16:32:23 
Objet: Re: [pve-devel] disabling transparent hugepage by default like kernel 2.6.32 ? 

Hi, 
In my benchmarks, THP increase the memory transaction speed by 5-10% in the KVM guest if THP is activated on the host side, not in the VM side. I know that THP for databases is bad, but we are not using THP in the guest where the database lives. Can someone provide some benchmarks for that case or further information? Any suggestions? 

On Wed, Sep 9, 2015 at 3:45 PM, Daniel Hunsaker < danhunsaker at gmail.com > wrote: 




What about setting CONFIG_TRANSPARENT_HUGEPAGE_ALWAYS = N? As I understand it, "not set" means "use the default setting the kernel devs think is the most sane for normal use", which in this case would be Y... 

On Wed, Sep 9, 2015, 06:58 Alexandre DERUMIER < aderumier at odiso.com > wrote: 

 
>>I could set it in kernel config, for example: 
>> 
>>CONFIG_TRANSPARENT_HUGEPAGE_MADVISE=y 
>> 
>>would that help? 

Well, this is like "echo madvise > /sys/kernel/mm/transparent_hugepage/enabled" 

But I don't see how to set never. 

maybe 

# CONFIG_TRANSPARENT_HUGEPAGE_ALWAYS is not set 
# CONFIG_TRANSPARENT_HUGEPAGE_MADVISE is not set 


But I don't known how to unset CONFIG_TRANSPARENT_HUGEPAGE_ALWAYS in the new pve-kernel package makefile ? 


I have tried to add 

PVE_CONFIG_OPTS= \ 
.. 
-d CONFIG_TRANSPARENT_HUGEPAGE_ALWAYS \ 
.. 

but it don't seem to work, I still have CONFIG_TRANSPARENT_HUGEPAGE_ALWAYS=Y in .config 

Any idea ? 



----- Mail original ----- 
De: "dietmar" < dietmar at proxmox.com > 
À: "aderumier" < aderumier at odiso.com >, "pve-devel" < pve-devel at pve.proxmox.com > 
Envoyé: Mercredi 9 Septembre 2015 06:33:05 
Objet: Re: [pve-devel] disabling transparent hugepage by default like kernel 2.6.32 ? 

> I think it's better to disable it by default. 
> 
> echo never > /sys/kernel/mm/transparent_hugepage/enabled. 
> 
> (I don't known what is the best way to disable it by default) 

I could set it in kernel config, for example: 

CONFIG_TRANSPARENT_HUGEPAGE_MADVISE=y 

would that help? 
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