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Date: Wed, 15 Aug 2012 18:22:58 +0400
From: Michael Tokarev <mjt@tls.msk.ru>
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Subject: Re: [Qemu-devel] qemu and transparent huge pages
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To: Avi Kivity <avi@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>, qemu-devel <qemu-devel@nongnu.org>

On 15.08.2012 16:51, Avi Kivity wrote:
> On 08/15/2012 03:45 PM, Michael Tokarev wrote:
>>
>> But apparently, THP does not work still, even with 2Mb
>> alignment: when running a guest, AnonHugePages in
>> /proc/meminfo stays at 0 - either in kvm mode or in tcg
>> mode.  Any idea why?  What else is needed for THP to work?
> 
> It does for me:
> 
> AnonHugePages:    368640 kB
> 
> Note the patch you reference doesn't impact thp, just kvm's ability to
> propagate them to the shadow page table.
> 
>>
>> This is quite a frequent question in #kvm IRC channel,
>> and I always suggested using -mem-path for this,  but
>> I'm curios why it doesn't work automatically when it
>> probably should?
>>
> 
> Please provide extra info, like the setting of
> /sys/kernel/mm/transparent_hugepage/enabled.

That was it - sort of.  Default value here is enabled=madvise.
When setting it to always the effect finally started appearing,
so it is actually working.

But can't qemu set MADV_HUGEPAGE flag too, so it works automatically?

Thanks,

/mjt