Windows XP Pagefile

[Horst Walter]

I've got the following question about the Page File under Windows XP.

My system has 2GB RAM. When I run a couple of applications 1,2 GB of
the physical RAM is used. Although I still have 0,8 GB physical RAM
available the Windows Task Manager already shows a usage of 1,12 GB
for the page file.

Can someone point out, why this happens. I'd rather expect no usage of
the page file as long RAM still is available.

[Colin Painter]

I am not positive, but I think that the page file space is reserved for
various contingencies. For example, you may be running an app that has
carved out a big virtual address space but only a fraction of these pages
actually exist. The space on the page file is reserved just in case your app
causes these pages to actually exist and some other app forces these pages
out. Doing this pre-reservation helps XP avoid memory management deadlocks.

cp

"Horst Walter" > wrote in message
om...
> I've got the following question about the Page File under Windows XP.
>
> My system has 2GB RAM. When I run a couple of applications 1,2 GB of
> the physical RAM is used. Although I still have 0,8 GB physical RAM
> available the Windows Task Manager already shows a usage of 1,12 GB
> for the page file.
>
> Can someone point out, why this happens. I'd rather expect no usage of
> the page file as long RAM still is available.

[John Holmes]

Colin Painter came up with this:

> I am not positive, but I think

Really?


--
"It ain't much, if it ain't Dutch..."

[Alex Nichol]

Horst Walter wrote:

>I've got the following question about the Page File under Windows XP.
>
>My system has 2GB RAM. When I run a couple of applications 1,2 GB of
>the physical RAM is used. Although I still have 0,8 GB physical RAM
>available the Windows Task Manager already shows a usage of 1,12 GB
>for the page file.
>
>Can someone point out, why this happens. I'd rather expect no usage of
>the page file as long RAM still is available.

Task Manager's 'use' for the page file is misleading. This is in
relation to pages which programs have asked to be allocated, but have
never brought into use (and most probably never will). They have to be
allocated to *something* so the system assigns then to *potential* spots
in a *potential* page file. If they come into use, some RAM will be
assigned instead - and if necessary some trivial use of RAM (eg caching
files that were accessed hours ago) will be dropped. But if there were
not the *possibility* of a page file, they would have to be assigned to
RAM, and lock some of it out to no purpose. The area of file does not
even have to exist - if you set it to have initial 50 Max say 1000 it
will almost certainly not grow beyond the 50 size (the system does tend
to park about 20 MB of items in it as a precaution)

Read more extensively at www.aumha.org/win5/a/xpvm.htm

--
Alex Nichol MS MVP (Windows Technologies)
Bournemouth, U.K. (remove the D8 bit)

[Horst Walter]

Thanks! Good article.
HW


Alex Nichol > wrote in message >...
> Horst Walter wrote:
>
> >I've got the following question about the Page File under Windows XP.
> >
> >My system has 2GB RAM. When I run a couple of applications 1,2 GB of
> >the physical RAM is used. Although I still have 0,8 GB physical RAM
> >available the Windows Task Manager already shows a usage of 1,12 GB
> >for the page file.
> >
> >Can someone point out, why this happens. I'd rather expect no usage of
> >the page file as long RAM still is available.
>
> Task Manager's 'use' for the page file is misleading. This is in
> relation to pages which programs have asked to be allocated, but have
> never brought into use (and most probably never will). They have to be
> allocated to *something* so the system assigns then to *potential* spots
> in a *potential* page file. If they come into use, some RAM will be
> assigned instead - and if necessary some trivial use of RAM (eg caching
> files that were accessed hours ago) will be dropped. But if there were
> not the *possibility* of a page file, they would have to be assigned to
> RAM, and lock some of it out to no purpose. The area of file does not
> even have to exist - if you set it to have initial 50 Max say 1000 it
> will almost certainly not grow beyond the 50 size (the system does tend
> to park about 20 MB of items in it as a precaution)
>
> Read more extensively at www.aumha.org/win5/a/xpvm.htm