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

Alexandre DERUMIER aderumier at odiso.com
Wed Sep 9 19:30:24 CEST 2015


Do you have tested it with a real workload and big memory ? (100-200GB for example).

I'm curious to see what happen with a lot of alloc/desalloc and fragmentation.


----- Mail original -----
De: "Andreas Steinel" <a.steinel at gmail.com>
À: "aderumier" <aderumier at odiso.com>
Cc: "Daniel Hunsaker" <danhunsaker at gmail.com>, "dietmar" <dietmar at proxmox.com>, "pve-devel" <pve-devel at pve.proxmox.com>
Envoyé: Mercredi 9 Septembre 2015 18:41:37
Objet: Re: [pve-devel] disabling transparent hugepage by default like kernel 2.6.32 ?

I tried with a simple 128 MB Jessie Box and 'mbw' program and got these results: 

mbw -n 100 50 | grep AVG > hthp_1_gthp_1 



HostTransparentHugePages_(1|0)_GuestTransparentHugePages_(1|0) 


Test hthp_0_gthp_0 
AVG Method: MEMCPY Elapsed: 0.01728 MiB: 50.00000 Copy: 
2893.123 MiB/s 
AVG Method: DUMB Elapsed: 0.01770 MiB: 50.00000 Copy: 
2824.581 MiB/s 
AVG Method: MCBLOCK Elapsed: 0.01111 MiB: 50.00000 Copy: 
4499.575 MiB/s 
Test hthp_0_gthp_1 
AVG Method: MEMCPY Elapsed: 0.01927 MiB: 50.00000 Copy: 
2594.132 MiB/s 
AVG Method: DUMB Elapsed: 0.01869 MiB: 50.00000 Copy: 
2674.970 MiB/s 
AVG Method: MCBLOCK Elapsed: 0.01157 MiB: 50.00000 Copy: 
4322.956 MiB/s 
Test hthp_1_gthp_0 
AVG Method: MEMCPY Elapsed: 0.01645 MiB: 50.00000 Copy: 
3039.115 MiB/s 
AVG Method: DUMB Elapsed: 0.01572 MiB: 50.00000 Copy: 
3180.148 MiB/s 
AVG Method: MCBLOCK Elapsed: 0.00987 MiB: 50.00000 Copy: 
5066.072 MiB/s 
Test hthp_1_gthp_1 
AVG Method: MEMCPY Elapsed: 0.02151 MiB: 50.00000 Copy: 
2324.526 MiB/s 
AVG Method: DUMB Elapsed: 0.01553 MiB: 50.00000 Copy: 
3220.203 MiB/s 
AVG Method: MCBLOCK Elapsed: 0.00998 MiB: 50.00000 Copy: 
5009.729 MiB/s 

On Wed, Sep 9, 2015 at 5:43 PM, Alexandre DERUMIER <aderumier at odiso.com> wrote: 
>>>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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