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Re: Support for Multiple Page Sizes

From: Espen Skoglund
Subject: Re: Support for Multiple Page Sizes
Date: Thu, 9 Aug 2007 17:25:43 +0200

[Neal H Walfield]
> Why Multiple Page Sizes
> -----------------------

> In Jochen's paper in which he describes guarded page tables he
> discusses fitting objects into the minimum number of pages possible.
> But is the common usage pattern to really access all bits of an
> object?  Today we don't swap tasks; we page them.  The justification
> is that only bits and pieces are used and the cost of the additional
> faults, memory and TLBs is generally less than the cost of paging
> the object as a whole.

> An exception to this observation is a rendered image.  In this case,
> the image is often either completely or wholly displayed on the
> screen (think web browser); the entirety of the object is used at
> once.

The main reason for wanting multiple page sizes is mostly to lower the
TLB footprint.  [2] gives a good summary of what the performance
advantages are and talks about various strategies for demoting and
promoting pages/superpages.


> [1] Page Table Structures For Fine-Grain Virtual Memory by Jochen
>     Liedtke (1994).

>     http://citeseer.ist.psu.edu/liedtke94page.html

[2] Practical, Transparent Operating System Support for Superpages,
    Juan Navarro, Sitaram Iyer, Peter Druschel, Alan Cox (2002)


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