VM Vs Swap space

hi

if somebody can tell me that is this correct?

can i say that swap area created by linux is nothign
but virtual memory. is it correct to use the term
interchangeably

thanks

ankit

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Re: VM Vs Swap space

Ankit Jain wrote:

>hi
>
>if somebody can tell me that is this correct?
>
>(1)can i say that swap area created by linux is nothign
>but virtual memory. (2)is it correct to use the term
>interchangeably
>
>thanks
>
>ankit
>
>
(1) A swap file or swap partition can be used as virtual memory.
(2) I am not sure. Why one would wish to use 'swap area'
interchangeably with 'virtual memory'.
:-|
Chuck


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Re: VM Vs Swap space

swap area forms a part of the memory which is used for the memory
objects like the stack when executable
starts running. This anonymous segment will grow dependin upon the
pattern of the functions calls in ur executable

On Wed, 06 Oct 2004 21:57:27 -0400, chuck gelm wrote:
> Ankit Jain wrote:
>
> >hi
> >
> >if somebody can tell me that is this correct?
> >
> >(1)can i say that swap area created by linux is nothign
> >but virtual memory. (2)is it correct to use the term
> >interchangeably
> >
> >thanks
> >
> >ankit
> >
> >
> (1) A swap file or swap partition can be used as virtual memory.
> (2) I am not sure. Why one would wish to use 'swap area'
> interchangeably with 'virtual memory'.
> :-|
> Chuck
>
>
>
>
> -
> To unsubscribe from this list: send the line "unsubscribe linux-newbie" in
> the body of a message to majordomo@vger.kernel.org
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Re: VM Vs Swap space

how will u differentiate virtual memory and swap area

thanks

ankit
--- chuck gelm wrote:
> Ankit Jain wrote:
>
> >hi
> >
> >if somebody can tell me that is this correct?
> >
> >(1)can i say that swap area created by linux is
> nothign
> >but virtual memory. (2)is it correct to use the
> term
> >interchangeably
> >
> >thanks
> >
> >ankit
> >
> >
> (1) A swap file or swap partition can be used as
> virtual memory.
> (2) I am not sure. Why one would wish to use 'swap
> area'
> interchangeably with 'virtual memory'.
> :-|
> Chuck
>
>
>

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Re: VM Vs Swap space

Virtual Memory is a policy. Swap Area is a artifact, u use to
implement this policy

Hope makes sense


On Thu, 7 Oct 2004 10:15:15 +0100 (BST), Ankit Jain
wrote:
> how will u differentiate virtual memory and swap area
>
> thanks
>
> ankit
> --- chuck gelm wrote:
> > Ankit Jain wrote:
> >
> > >hi
> > >
> > >if somebody can tell me that is this correct?
> > >
> > >(1)can i say that swap area created by linux is
> > nothign
> > >but virtual memory. (2)is it correct to use the
> > term
> > >interchangeably
> > >
> > >thanks
> > >
> > >ankit
> > >
> > >
> > (1) A swap file or swap partition can be used as
> > virtual memory.
> > (2) I am not sure. Why one would wish to use 'swap
> > area'
> > interchangeably with 'virtual memory'.
> > :-|
> > Chuck
> >
> >
> >
>
> ____________________________________________________________ ____________
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Re: VM Vs Swap space

well if we dont have a swap area then shall i say my
system dosent have virtual memory

is this correct? because i feel even if this swap area
is not there then also virtual memory concept exists?

thanks

ankit
--- kernel kernel wrote:
> Virtual Memory is a policy. Swap Area is a
> artifact, u use to
> implement this policy
>
> Hope makes sense
>
>
> On Thu, 7 Oct 2004 10:15:15 +0100 (BST), Ankit Jain
> wrote:
> > how will u differentiate virtual memory and swap
> area
> >
> > thanks
> >
> > ankit
> > --- chuck gelm wrote:
> > > Ankit Jain wrote:
> > >
> > > >hi
> > > >
> > > >if somebody can tell me that is this correct?
> > > >
> > > >(1)can i say that swap area created by linux is
> > > nothign
> > > >but virtual memory. (2)is it correct to use the
> > > term
> > > >interchangeably
> > > >
> > > >thanks
> > > >
> > > >ankit
> > > >
> > > >
> > > (1) A swap file or swap partition can be used as
> > > virtual memory.
> > > (2) I am not sure. Why one would wish to use
> 'swap
> > > area'
> > > interchangeably with 'virtual memory'.
> > > :-|
> > > Chuck
> > >
> > >
> > >
> >
> >
>
____________________________________________________________ ____________
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> "unsubscribe linux-newbie" in
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> http://www.linux-learn.org/faqs
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>

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Re: VM Vs Swap space

Ankit Jain wrote:

>well if we dont have a swap area then shall i say my
>system dosent have virtual memory
>
>
Yes, I think so. I think that it is difficult to say that a system
has no 'swap area', because a 'swap area' could be a file.

How can you be sure that none of the files on a system are
a 'swap file' ?

I think that you can say that a system has no 'swap' or 'virtual memory'
if there are no swap areas enabled.

I suggest that the output of 'free' will indicate your swap.
If 'free' indicates that you have no swap, then you have no swap.
If 'free' indicates that you have swap, then you have swap.

>is this correct? because i feel even if this swap area
>is not there then also virtual memory concept exists?
>
A system can have a swap partition and not use it.
A system can have a swap file and not use it.
Swap can be enabled and disabled on a running kernel.
So, at any given instance, a running system can have
or have not 'virtual memory'.

>thanks
>
>ankit
>--- kernel kernel wrote:
>
>
>>Virtual Memory is a policy. Swap Area is a
>>artifact, u use to
>>implement this policy
>>
>>Hope makes sense
>>
>>
>>On Thu, 7 Oct 2004 10:15:15 +0100 (BST), Ankit Jain
>> wrote:
>>
>>
>>>how will u differentiate virtual memory and swap
>>>
>>>
>>area
>>
>>
>>>thanks
>>>
>>>ankit
>>>--- chuck gelm wrote:
>>>
>>>
>>>>Ankit Jain wrote:
>>>>
>>>>
>>>>
>>>>>hi
>>>>>
>>>>>if somebody can tell me that is this correct?
>>>>>
>>>>>(1)can i say that swap area created by linux is
>>>>>
>>>>>
>>>>nothign
>>>>
>>>>
>>>>>but virtual memory. (2)is it correct to use the
>>>>>
>>>>>
>>>>term
>>>>
>>>>
>>>>>interchangeably
>>>>>
>>>>>thanks
>>>>>
>>>>>ankit
>>>>>
>>>>>
>>>>>
>>>>>
>>>>(1) A swap file or swap partition can be used as
>>>>virtual memory.
>>>>(2) I am not sure. Why one would wish to use
>>>>
>>>>
>>'swap
>>
>>
>>>>area'
>>>>interchangeably with 'virtual memory'.
>>>>:-|
>>>>Chuck
>>>>
>>>>


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Re: VM Vs Swap space

Ankit Jain wrote:

>how will u differentiate virtual memory and swap area
>
>thanks
>
>ankit
>
>
Virtual memory is swap area in use.

Regards, Chuck

> --- chuck gelm wrote:
>
>
>>Ankit Jain wrote:
>>
>>
>>
>>>hi
>>>
>>>if somebody can tell me that is this correct?
>>>
>>>(1)can i say that swap area created by linux is
>>>
>>>
>>nothign
>>
>>
>>>but virtual memory. (2)is it correct to use the
>>>
>>>
>>term
>>
>>
>>>interchangeably
>>>
>>>thanks
>>>
>>>ankit
>>>
>>>
>>>
>>>
>>(1) A swap file or swap partition can be used as
>>virtual memory.
>>(2) I am not sure. Why one would wish to use 'swap
>>area'
>>interchangeably with 'virtual memory'.
>>:-|
>>Chuck
>>
>>


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Re: VM Vs Swap space

On Thu, 7 Oct 2004 10:37:40 +0100 (BST), Ankit Jain
wrote:
> well if we dont have a swap area then shall i say my
> system dosent have virtual memory

No.

> is this correct? because i feel even if this swap area
> is not there then also virtual memory concept exists?

Virtual memory is the reason why applications can think they have 4GB
of memory while your physical machine might actually have only 32MB.
You don't need to have swap in order to have virtual memory, although
its very advantageous to have swap with VM.

Virtual memory maps the viurtual pages (from 0 to 4GB) to actually
physical memory pages (from 0 to however much RAM you have). Swapping
is the process of using the disk to store physical memory pages when
they are not in use, and then restoring them when an application
accesses them.
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Re: VM Vs Swap space

On Thu, 7 Oct 2004 10:37:40 +0100 (BST), Ankit Jain
wrote:
> well if we dont have a swap area then shall i say my
> system dosent have virtual memory

No.

> is this correct? because i feel even if this swap area
> is not there then also virtual memory concept exists?

Virtual memory is the reason why applications can think they have 4GB
of memory while your physical machine might actually have only 32MB.
You don't need to have swap in order to have virtual memory, although
its very advantageous to have swap with VM.

Virtual memory maps the viurtual pages (from 0 to 4GB) to actually
physical memory pages (from 0 to however much RAM you have). Swapping
is the process of using the disk to store physical memory pages when
they are not in use, and then restoring them when an application
accesses them.

Pratik.
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Re: VM Vs Swap space

On Thu, 07 Oct 2004 06:41:38 -0400, chuck gelm wrote:
> Ankit Jain wrote:
>
> >how will u differentiate virtual memory and swap area
> >
> >thanks
> >
> >ankit
> >
> >
> Virtual memory is swap area in use.

umm. A running system can or cannot have swap. Correct me if I am
wrong but you can't disable virtual memory once its enabled, or at the
very least it would be extremely tough to do so and I don't know of
any system that does it. Virtual memory is enabled when the kernel
starts up and stays that way. Swap is a different issue.

Pratik.
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Re: VM Vs Swap space

Yes. 32 bit address = 2^32 addresses = 4GB

For a 64-bit machine, the limit is 2^64.

Pratik.

On Thu, 7 Oct 2004 17:06:56 +0100 (BST), Ankit Jain
wrote:
> why limit is upto 4 GB is it due to address bus limit?
>
> thanks
>
> ankit
> --- Pratik Solanki
> wrote:
>
>
> > On Thu, 7 Oct 2004 10:37:40 +0100 (BST), Ankit Jain
> > wrote:
> > > well if we dont have a swap area then shall i say
> > my
> > > system dosent have virtual memory
> >
> > No.
> >
> > > is this correct? because i feel even if this swap
> > area
> > > is not there then also virtual memory concept
> > exists?
> >
> > Virtual memory is the reason why applications can
> > think they have 4GB
> > of memory while your physical machine might actually
> > have only 32MB.
> > You don't need to have swap in order to have virtual
> > memory, although
> > its very advantageous to have swap with VM.
> >
> > Virtual memory maps the viurtual pages (from 0 to
> > 4GB) to actually
> > physical memory pages (from 0 to however much RAM
> > you have). Swapping
> > is the process of using the disk to store physical
> > memory pages when
> > they are not in use, and then restoring them when an
> > application
> > accesses them.
> >
> > Pratik.
> >
>
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Re: VM Vs Swap space

[CCing linux-newbie]

On Thu, 7 Oct 2004 18:21:57 +0100 (BST), Ankit Jain
wrote:
> well i dont know exactly but somewhat i feel that
> there must be some way to disable the virtual memory.
> yaa of course there should be some way. it is not that
> sys cant work without it

Yes, you can have a system without virtual memory. Search for MMUless
linux kernel and you'll see patches/websites.

My point was that disabling VM after its been enabled would tough (if
not impossible). Someone correct me if I am wrong here.

Pratik.

> ankit
> --- Pratik Solanki
> wrote:
>
>
> > On Thu, 07 Oct 2004 06:41:38 -0400, chuck gelm
> > wrote:
> > > Ankit Jain wrote:
> > >
> > > >how will u differentiate virtual memory and swap
> > area
> > > >
> > > >thanks
> > > >
> > > >ankit
> > > >
> > > >
> > > Virtual memory is swap area in use.
> >
> > umm. A running system can or cannot have swap.
> > Correct me if I am
> > wrong but you can't disable virtual memory once its
> > enabled, or at the
> > very least it would be extremely tough to do so and
> > I don't know of
> > any system that does it. Virtual memory is enabled
> > when the kernel
> > starts up and stays that way. Swap is a different
> > issue.
> >
> > Pratik.
> > -
> > To unsubscribe from this list: send the line
> > "unsubscribe linux-newbie" in
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> > More majordomo info at
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> > Please read the FAQ at
> > http://www.linux-learn.org/faqs
>
>
> >
>
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Re: VM Vs Swap space

Pratik Solanki wrote:

>[CCing linux-newbie]
>
>On Thu, 7 Oct 2004 18:21:57 +0100 (BST), Ankit Jain
> wrote:
>
>
>>well i dont know exactly but somewhat i feel that
>>there must be some way to disable the virtual memory.
>>yaa of course there should be some way. it is not that
>>sys cant work without it
>>
>>
>
>Yes, you can have a system without virtual memory. Search for MMUless
>linux kernel and you'll see patches/websites.
>
>My point was that disabling VM after its been enabled would tough (if
>not impossible). Someone correct me if I am wrong here.
>
>Pratik.
>
I was thinking that an active swap partition was 'virtual memory'.
Why are many folks using capital letters 'VM'. Am I missing
something? Is 'VM' == virtual memory or is there a application
or service called 'VM' ?

Anywho, the only 'virtual memory' I know of is an active
swap file or swap partition and either can be started
or stopped in a running kernel.
(I think.)

Regards, Chuck


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Re: VM Vs Swap space

chuck gelm wrote:

> Pratik Solanki wrote:
>
>> [CCing linux-newbie]
>>
>> On Thu, 7 Oct 2004 18:21:57 +0100 (BST), Ankit Jain
>> wrote:
>>
>>
>>> well i dont know exactly but somewhat i feel that
>>> there must be some way to disable the virtual memory.
>>> yaa of course there should be some way. it is not that
>>> sys cant work without it
>>>
>>
>>
>> Yes, you can have a system without virtual memory. Search for MMUless
>> linux kernel and you'll see patches/websites.
>>
>> My point was that disabling VM after its been enabled would tough (if
>> not impossible). Someone correct me if I am wrong here.
>>
>> Pratik.
>>
> I was thinking that an active swap partition was 'virtual memory'.
> Why are many folks using capital letters 'VM'. Am I missing
> something? Is 'VM' == virtual memory or is there a application
> or service called 'VM' ?
>
> Anywho, the only 'virtual memory' I know of is an active
> swap file or swap partition and either can be started
> or stopped in a running kernel.
> (I think.)
>
> Regards, Chuck



From "Understanding the Linux Kernel":

"Virtual memory acts as a logical layer between the application memory
requests and the hardware Memory Management Unit (MMU)."

It is an abstraction of system memory to provide an
architecture-independent memory interface. It allows for a great many
things, including swap functionality, but its primary function is to
make the details of memory management invisible to application
programmers. You just malloc() some memory, and you don't have to worry
overmuch about far jumps, hardware cache alignment, or other annoying stuff.

It also allows large malloc() calls to succeed, even if physical memory
is completely fragmented, by maintaining a set of page tables that allow
virtual-to-physical mapping of memory addresses.

This is one of the most challenging areas of kernel development, and
very hardware-specific. I tried to understand how it worked recently,
gave myself a splitting headache after 30 minutes, and decided to let it
sit for another year or so until I understand kernel internals, computer
architecture, and assembler much better than I do now :)

Jim
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Re: VM Vs Swap space

In That case, also. There is a implicit Swap area and a Explicit area.


On Thu, 7 Oct 2004 12:07:21 -0400, Pratik Solanki
wrote:
> On Thu, 7 Oct 2004 10:37:40 +0100 (BST), Ankit Jain
> wrote:
> > well if we dont have a swap area then shall i say my
> > system dosent have virtual memory
>
> No.
>
> > is this correct? because i feel even if this swap area
> > is not there then also virtual memory concept exists?
>
> Virtual memory is the reason why applications can think they have 4GB
> of memory while your physical machine might actually have only 32MB.
> You don't need to have swap in order to have virtual memory, although
> its very advantageous to have swap with VM.
>
> Virtual memory maps the viurtual pages (from 0 to 4GB) to actually
> physical memory pages (from 0 to however much RAM you have). Swapping
> is the process of using the disk to store physical memory pages when
> they are not in use, and then restoring them when an application
> accesses them.
>
> Pratik.
>
>
> -
> To unsubscribe from this list: send the line "unsubscribe linux-newbie" in
> the body of a message to majordomo@vger.kernel.org
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Re: VM Vs Swap space

On Thu, 07 Oct 2004 18:13:52 -0400, chuck gelm wrote:
> Pratik Solanki wrote:
>
> >[CCing linux-newbie]
> >
> >On Thu, 7 Oct 2004 18:21:57 +0100 (BST), Ankit Jain
> > wrote:
> >
> >
> >>well i dont know exactly but somewhat i feel that
> >>there must be some way to disable the virtual memory.
> >>yaa of course there should be some way. it is not that
> >>sys cant work without it
> >>
> >>
> >
> >Yes, you can have a system without virtual memory. Search for MMUless
> >linux kernel and you'll see patches/websites.
> >
> >My point was that disabling VM after its been enabled would tough (if
> >not impossible). Someone correct me if I am wrong here.
> >
> >Pratik.
> >
> I was thinking that an active swap partition was 'virtual memory'.
> Why are many folks using capital letters 'VM'. Am I missing
> something? Is 'VM' == virtual memory or is there a application
> or service called 'VM' ?

Yes, VM is virtual memory.

> Anywho, the only 'virtual memory' I know of is an active
> swap file or swap partition and either can be started
> or stopped in a running kernel.
> (I think.)

Swap can be started or stopped. Virtual memory cannot be started or
stopped. Just because you stopped swap does not mean the kernel is not
using virtual memory. The kernel always uses virtual memory (except if
its MMUless) . Swap is used only when the kernel needs more memory
than what's physically available.

Pratik.
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