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How many page flags do we really have?

How many page flags do we really have?

Posted Jun 7, 2009 1:12 UTC (Sun) by giraffedata (subscriber, #1954)
Parent article: How many page flags do we really have?

Why are people willing to accept 4 bytes per physical page waste on a 64 bit system, but not on a 32 bit system?


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How many page flags do we really have?

Posted Jun 7, 2009 9:33 UTC (Sun) by farnz (subscriber, #17727) [Link]

One difference is the size of lowmem. On a 32-bit system, those 4 bytes per page all come out of the first 896MB of physical RAM. On a 64-bit system, they come out of your total RAM. It's a lot easier to accept waste when it's not in such a tightly restricted block of memory; we already have problems with running low on lowmem on 32-bit systems with more than around 8GB RAM, which are best solved by going to 64-bit.

How many page flags do we really have?

Posted Jul 10, 2009 17:45 UTC (Fri) by sethml (guest, #8471) [Link]

Yeah, I was left wondering why the page flags are an unsigned long rather than a uint32_t?
Surely in such a space constrained data structure it's best to use only as many bits as
necessary?


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