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weirdness in bootmem_init(), arch/mips64/kernel/setup.c

To: Linux-MIPS <linux-mips@linux-mips.org>
Subject: weirdness in bootmem_init(), arch/mips64/kernel/setup.c
From: Andrew Clausen <clausen@melbourne.sgi.com>
Date: Tue, 18 Feb 2003 17:54:27 +1100
Original-recipient: rfc822;linux-mips@linux-mips.org
Sender: linux-mips-bounce@linux-mips.org
User-agent: Mutt/1.4i
Hi all,

This code isn't really relevant to what I'm working on (it isn't compiled
in to kernels for the ip27), but I just noticed it, and it looks broken:

        /* Find the highest page frame number we have available.  */
        max_pfn = 0;
        for (i = 0; i < boot_mem_map.nr_map; i++) {
                unsigned long start, end;

                if (boot_mem_map.map[i].type != BOOT_MEM_RAM)
                        continue;

*****           start = PFN_UP(boot_mem_map.map[i].addr);
*****           end = PFN_DOWN(boot_mem_map.map[i].addr
                      + boot_mem_map.map[i].size);

*****           if (start >= end)
                        continue;
                if (end > max_pfn)
                        max_pfn = end;
        }


That test looks like it will always succeed... and it looks like the
author wanted it to be a sanity check.

Why all this business with PFN_UP and PFN_DOWN?  (They are bit
shifts... PFN_UP shifts left, PFN_DOWN shifts right)

Cheers,
Andrew


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