context overflow

[Paul Mackerras]

Gabriel Paubert writes:

> > CONFIG_HIGHMEM has little to do with the kernel virtual space. The main
> > purpose is to get the memory into user space, where user programs can use
> > them. I really don't understand, what problem you're trying to solve. The
> > kernel only wants to manage high memory and rarely access it (and uses
> > kmap for this), most of the time these pages should be in the user virtual
> > address space only.
>
> Confused. If you have up to 64 Gb or RAM (the 7450 has 36 address lines)
> and can use not even use one gigabyte for cache, you end up with a
> seriously unbalanced system. Depending on what you do of course.

The highmem pages are used mainly as page-cache pages and anonymous
user pages.  At the moment the kernel uses bounce buffers for doing
I/O to/from highmem pages but that is on the list of things to be
fixed. :)

Paul.

--
Paul Mackerras, Open Source Research Fellow, Linuxcare, Inc.
+61 2 6262 8990 tel, +61 2 6262 8991 fax
paulus at linuxcare.com.au, http://www.linuxcare.com.au/
Linuxcare.  Putting open source to work.

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