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