Physical memory fragmentation

Dmitriy Vyukov

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Apr 12, 2009, 9:32:11 AM4/12/09

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Is there any way to programmatically de-fragment physical memory on
latest versions of Windows (Vista, Server 2008)? I need it for
allocation of large pages (MEM_LARGE_PAGES). Instantly after boot I am
able to allocate ~250 2MB large pages (machine has 2GB of physical
memory), but after some time I am able to allocate 0 large pages. As
far as I understand this relates to physical memory fragmentation.

p.s. I am not allowed to install own service to pre-allocate large
pages.

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Best regards,
Dmitriy V'jukov

Nathan Mates

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Apr 12, 2009, 12:21:19 PM4/12/09

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In article <71cc459a-dc01-4490...@t11g2000vbc.googlegroups.com>,

Dmitriy Vyukov <dvy...@gmail.com> wrote:
>Is there any way to programmatically de-fragment physical memory on
>latest versions of Windows (Vista, Server 2008)? I need it for
>allocation of large pages (MEM_LARGE_PAGES). Instantly after boot I am
>able to allocate ~250 2MB large pages (machine has 2GB of physical
>memory), but after some time I am able to allocate 0 large pages. As
>far as I understand this relates to physical memory fragmentation.

If you need large chunks of RAM, then you really should be
considering going to a 64-bit OS. Vista and Server 2008 both have
64-bit flavors. You can allocate *MUCH* more memory on them.

Nathan Mates

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<*> Nathan Mates - personal webpage http://www.visi.com/~nathan/
# Programmer at Pandemic Studios -- http://www.pandemicstudios.com/
# NOT speaking for Pandemic Studios. "Care not what the neighbors
# think. What are the facts, and to how many decimal places?" -R.A. Heinlein

scot...@mvps.org

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Apr 12, 2009, 12:44:11 PM4/12/09

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On Apr 12, 12:21 pm, nat...@visi.com (Nathan Mates) wrote:

> Dmitriy Vyukov <dvyu...@gmail.com> wrote:
>
> >Is there any way to programmatically de-fragment physical memory on
> >latest versions of Windows (Vista, Server 2008)? I need it for
> >allocation of large pages (MEM_LARGE_PAGES). Instantly after boot I am
> >able to allocate ~250 2MB large pages (machine has 2GB of physical
> >memory), but after some time I am able to allocate 0 large pages. As
> >far as I understand this relates to physical memory fragmentation.

Have you tried it without the MEM_LARGE_PAGES bit? 2 MB is not very
"large".

Dmitriy Vyukov

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Apr 13, 2009, 1:58:35 AM4/13/09

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On Apr 12, 8:21 pm, nat...@visi.com (Nathan Mates) wrote:
> In article <71cc459a-dc01-4490-848f-e684f7368...@t11g2000vbc.googlegroups.com>,

> Dmitriy Vyukov <dvyu...@gmail.com> wrote:
>
> >Is there any way to programmatically de-fragment physical memory on
> >latest versions of Windows (Vista, Server 2008)? I need it for
> >allocation of large pages (MEM_LARGE_PAGES). Instantly after boot I am
> >able to allocate ~250 2MB large pages (machine has 2GB of physical
> >memory), but after some time I am able to allocate 0 large pages. As
> >far as I understand this relates to physical memory fragmentation.
>
> If you need large chunks of RAM, then you really should be
> considering going to a 64-bit OS. Vista and Server 2008 both have
> 64-bit flavors. You can allocate *MUCH* more memory on them.

64-bit OS has something to do only with process' virtual address
space. It has nothing to do with physical memory.
64-bit Windows has exactly the same problems with large pages as 32-
bit Windows.

Dmitriy Vyukov

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Apr 13, 2009, 2:03:45 AM4/13/09

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Yes, I tried it w/o the MEM_LARGE_PAGES, and memory is allocated w/o
problems then. 2MB is indeed not very large for process' virtual
space, though as it turns out is *very* large for continuous physical
memory.