Hello all,
I can't undestand one thing in kernel source,
so if anybody has information about it,
please sched the light on it.
There is a max_pfn variable. According to the comment
this is "the highest page frame number we have available"
It is calculated on x86 while iterating over memory regions:
for (i = 0; i < e820.nr_map; i++) {
unsigned long start, end;
/* RAM? */
if (e820.map[i].type != E820_RAM)
continue;
start = PFN_UP(e820.map[i].addr);
end = PFN_DOWN(e820.map[i].addr + e820.map[i].size);
if (start >= end)
continue;
if (end > max_pfn)
max_pfn = end;
memory_present(0, start, end);
}
4GB RAM is installed on my node, 32 bit kernel,
4 * 1024 * 1024 / 4 = 1024 * 1024 = 1048576 page frames.
Page frames are counted starting from 0, so, I suppose,
max_pfn should equal 1048575.
However on my real node max_pfn = 1048576.
I think, that we should change
end = PFN_DOWN(e820.map[i].addr + e820.map[i].size);
to
end = PFN_DOWN(e820.map[i].addr + e820.map[i].size - 1);
What do you think about it, do I miss something?
Thanks.
--
Vasily Tarasov,
tarasov.vasily@xxxxxxxxx
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