Duncan wrote:
I'm /definitely/ not sure on this, hopefully someone else will correct me
if I'm wrong, but I /believe/ "virtual address space" or "virtual memory"
in this case means something other than swap. I /believe/ swap would
still be part of the physical memory address space.
well, I did a bit of research, and I'm not certain you're correct.
$ less /usr/src/linux/Documentation/x86_64/mm.txt
from this lil document, you can see that user apps have 47 bits of
addressable space. From what I read, the kernel can map any portion of
the physical memory (40 bits) into these 47 bits for the process.
However, Linux supports 46 bits of physical address mapping instead of
40. I guess linux just doesn't use the extra bits, but has them there
"just in case". In addition to mapping the physical to virtual
addresses, the kernel then swap out those virtual pages to disk. So I
believe the kernel could access 256TB of swap, although it would be VERY
slow to read anything approaching 0.3% swap usage back into main memory.
I'd like to find better references, but below is what I was able to come
up with.
References:
http://en.wikipedia.org/wiki/Virtual_memory
http://www.linux-tutorial.info/modules.php?name=Tutorial&pageid=261
http://www.thejemreport.com/mambo/content/view/160/42/
http://os.newsforge.com/article.pl?sid=05/03/30/1242206&tid=152&tid=2&tid=150&tid=74
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