qemu/kvm memory allocation

qemu/kvm memory allocation

[Alexei Fedotov]

Hi engineers,

Could anyone direct me where memory allocation [1] for a new virtual
machine takes place in the code? I want to understand why the memory
is initialized with zeroes when I call malloc in a virtual machine.


[1] http://www.linux-kvm.org/page/Memory


--
With best regards / с наилучшими пожеланиями,
Alexei Fedotov / Алексей Федотов,
http://dataved.ru/
+7 916 562 8095

[1] Start using Apache Openmeetings today, http://openmeetings.apache.org/
[2] Join Alexei Fedotov @linkedin, http://ru.linkedin.com/in/dataved/
[3] Join Alexei Fedotov @facebook, http://www.facebook.com/openmeetings

Re: qemu/kvm memory allocation

[Paolo Bonzini]

Il 04/07/2014 16:49, Alexei Fedotov ha scritto:
> Hi engineers,
>
> Could anyone direct me where memory allocation [1] for a new virtual
> machine takes place in the code? I want to understand why the memory
> is initialized with zeroes when I call malloc in a virtual machine.

Nowhere in KVM.

Memory allocation happens in userspace, which usually (but not 
necessarily) means QEMU.  Quoting from the wiki page you mentioned:

> The qemu/kvm process runs mostly like a normal Linux program. It
> allocates its memory with normal malloc() or mmap() calls. If a guest is
> going to have 1GB of physical memory, qemu/kvm will effectively do a
> malloc(1<<30), allocating 1GB of host virtual space. However, just like
> a normal program doing a malloc(), there is no actual physical memory
> allocated at the time of the malloc(). It will not be actually allocated
> until the first time it is touched.

Paolo

Re: qemu/kvm memory allocation

[Alexei Fedotov]

Paolo, thank you.
--
With best regards / с наилучшими пожеланиями,
Alexei Fedotov / Алексей Федотов,
http://dataved.ru/
+7 916 562 8095

[1] Start using Apache Openmeetings today, http://openmeetings.apache.org/
[2] Join Alexei Fedotov @linkedin, http://ru.linkedin.com/in/dataved/
[3] Join Alexei Fedotov @facebook, http://www.facebook.com/openmeetings


On Fri, Jul 4, 2014 at 8:17 PM, Paolo Bonzini <pbonzini@redhat.com> wrote:
> Il 04/07/2014 16:49, Alexei Fedotov ha scritto:
>
>> Hi engineers,
>>
>> Could anyone direct me where memory allocation [1] for a new virtual
>> machine takes place in the code? I want to understand why the memory
>> is initialized with zeroes when I call malloc in a virtual machine.
>
>
> Nowhere in KVM.
>
> Memory allocation happens in userspace, which usually (but not necessarily)
> means QEMU.  Quoting from the wiki page you mentioned:
>
>> The qemu/kvm process runs mostly like a normal Linux program. It
>> allocates its memory with normal malloc() or mmap() calls. If a guest is
>> going to have 1GB of physical memory, qemu/kvm will effectively do a
>> malloc(1<<30), allocating 1GB of host virtual space. However, just like
>> a normal program doing a malloc(), there is no actual physical memory
>> allocated at the time of the malloc(). It will not be actually allocated
>> until the first time it is touched.
>
>
> Paolo

Re: qemu/kvm memory allocation

[Alexei Fedotov]

Hi Paolo, all,

could anyone advise which source file implements memory allocation in
KVM? I want to check the source of the corresponding malloc. A simple
search says that
KVM source tree contains three malloc implementations.


--
With best regards / с наилучшими пожеланиями,
Alexei Fedotov / Алексей Федотов,
http://dataved.ru/
+7 916 562 8095

[1] Start using Apache Openmeetings today, http://openmeetings.apache.org/
[2] Join Alexei Fedotov @linkedin, http://ru.linkedin.com/in/dataved/
[3] Join Alexei Fedotov @facebook, http://www.facebook.com/openmeetings


On Mon, Jul 7, 2014 at 1:35 PM, Alexei Fedotov <alexei.fedotov@gmail.com> wrote:
> Paolo, thank you.
> --
> With best regards / с наилучшими пожеланиями,
> Alexei Fedotov / Алексей Федотов,
> http://dataved.ru/
> +7 916 562 8095
>
> [1] Start using Apache Openmeetings today, http://openmeetings.apache.org/
> [2] Join Alexei Fedotov @linkedin, http://ru.linkedin.com/in/dataved/
> [3] Join Alexei Fedotov @facebook, http://www.facebook.com/openmeetings
>
>
> On Fri, Jul 4, 2014 at 8:17 PM, Paolo Bonzini <pbonzini@redhat.com> wrote:
>> Il 04/07/2014 16:49, Alexei Fedotov ha scritto:
>>
>>> Hi engineers,
>>>
>>> Could anyone direct me where memory allocation [1] for a new virtual
>>> machine takes place in the code? I want to understand why the memory
>>> is initialized with zeroes when I call malloc in a virtual machine.
>>
>>
>> Nowhere in KVM.
>>
>> Memory allocation happens in userspace, which usually (but not necessarily)
>> means QEMU.  Quoting from the wiki page you mentioned:
>>
>>> The qemu/kvm process runs mostly like a normal Linux program. It
>>> allocates its memory with normal malloc() or mmap() calls. If a guest is
>>> going to have 1GB of physical memory, qemu/kvm will effectively do a
>>> malloc(1<<30), allocating 1GB of host virtual space. However, just like
>>> a normal program doing a malloc(), there is no actual physical memory
>>> allocated at the time of the malloc(). It will not be actually allocated
>>> until the first time it is touched.
>>
>>
>> Paolo

Re: qemu/kvm memory allocation

[Paolo Bonzini]

Il 11/07/2014 16:35, Alexei Fedotov ha scritto:
> Hi Paolo, all,
>
> could anyone advise which source file implements memory allocation in
> KVM? I want to check the source of the corresponding malloc. A simple
> search says that
> KVM source tree contains three malloc implementations.

I'm not even sure what you're talking about, since I already told you 
that the KVM hypervisor does not do any memory allocation.

Paolo

Re: qemu/kvm memory allocation

[Anshul Makkar]

kvm and QEMU are different..

On Fri, Jul 11, 2014 at 4:58 PM, Paolo Bonzini <pbonzini@redhat.com> wrote:
> Il 11/07/2014 16:35, Alexei Fedotov ha scritto:
>
>> Hi Paolo, all,
>>
>> could anyone advise which source file implements memory allocation in
>> KVM? I want to check the source of the corresponding malloc. A simple
>> search says that
>> KVM source tree contains three malloc implementations.
>
>
> I'm not even sure what you're talking about, since I already told you that
> the KVM hypervisor does not do any memory allocation.
>
>
> Paolo
> --
> To unsubscribe from this list: send the line "unsubscribe kvm" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html

Re: qemu/kvm memory allocation

[Alexei Fedotov]

Guys, thanks for guiding me. I'm looking into qemu sources right now.

--
With best regards / с наилучшими пожеланиями,
Alexei Fedotov / Алексей Федотов,
http://dataved.ru/
+7 916 562 8095

[1] Start using Apache Openmeetings today, http://openmeetings.apache.org/
[2] Join Alexei Fedotov @linkedin, http://ru.linkedin.com/in/dataved/
[3] Join Alexei Fedotov @facebook, http://www.facebook.com/openmeetings


On Fri, Jul 11, 2014 at 6:58 PM, Paolo Bonzini <pbonzini@redhat.com> wrote:
> Il 11/07/2014 16:35, Alexei Fedotov ha scritto:
>
>> Hi Paolo, all,
>>
>> could anyone advise which source file implements memory allocation in
>> KVM? I want to check the source of the corresponding malloc. A simple
>> search says that
>> KVM source tree contains three malloc implementations.
>
>
> I'm not even sure what you're talking about, since I already told you that
> the KVM hypervisor does not do any memory allocation.
>
> Paolo