Question concerning memory configuration variables

I have been looking at 2.2.23 and noticed that a few things concerning memory
paging has changed. I wonder if anybody could give me a definition of a couple
of the variables that are defined. The first is the max_low_pfn variable. It looks
like the first time that I see this called is during the paging_init() function and
passed to free_area_init(). The memory map size is determined from
this variable.
It memory map will extend to the end of physical memory (what used to be mips_memory_
upper). Do I determine the max_low_pfn by calculating the available memory and subtract
the size of the kernel? How does the variable "start" play into this equation? Are they
the same? Any help would be greatly appreciated.

Thanks,
Jeff

--
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Jeff Harrell Work: (801) 619-6104
Broadband Access group/TI
[email protected]
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The max_low_pfn variable is the number of `normal' memory pages. Normal as opposed to high memory which we don't currently don't support on MIPS. That is for contiguous memory starting at physical address zero it's value equals available_memory / PAGE_SIZE.

The value of max_low_pfn is set by a call to init_bootmem. A typical setup could look like below. Mb in this example is the number of available megabytes of memory. You may simplify this somewhat more, it's derived from the Origin code.

        free_start = PFN_ALIGN(&_end) - PAGE_OFFSET;
        free_end = PAGE_OFFSET + (mb << 20);
        start_pfn = PFN_UP((unsigned long)&_end - PAGE_OFFSET);

        /* Register all the contiguous memory with the bootmem allocator
           and free it.  Be careful about the bootmem freemap.  */
        bootmap_size = init_bootmem(start_pfn, mb << (20 - PAGE_SHIFT));

	/* Free the entire available memory after the _end symbol.  */
        free_bootmem(__pa(free_start), (mb << 20) - __pa(free_start));

	/* We also did free the memory where the bootmap is stored,
	   reserve it again. */
        reserve_bootmem(__pa(free_start), bootmap_size);

        printk("Found %ldmb of memory.\n", mb);

Ralf