On Thu, 22 Apr 1999 21:41:38 +0200 (CEST), Andrea Arcangeli
<andrea@e-mind.com> said:
> On Thu, 22 Apr 1999, Timo Ketola wrote:
>> 2) The kernel message says that 412k of the memory is reserved. I'm
>> afraid that the 640k-1M area is reserved and lost. If thats true, how
>> can I get them back.
> I don't think you loose memory. reserved should be memory used by the
> kernel too.
No. If there is phsyical memory at those addresses, you can't use it.
Look at arch/i386/mm/init.c, function mem_init(): basically we have
already marked all memory as reserved by this point, and we now go
through the low memory (below 0x9F0000) and high memory (above 1MB)
clearing the PG_reserved bits. Once we've done that, we do a
free_page() on all non-reserved pages to place them on the kernel free
list. The reserved pages never make it onto the free lists so are never
allocated by the kernel.
The kernel _does_ let you play with reserved pages to some extent, for
example to allow mmap()ing of ISA framebuffers into process address
space. However, the VM is careful to tread carefully around those
reserved pages, not performing any demand-paging or swapping on them.
--Stephen
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