Rohit> I'm afraid you may be wasting a lot of extra memory by
Rohit> replicaitng these PTEs(Take an example of one 4G large TLB
Rohit> size entry and assume there are few hunderd processes using
Rohit> that same physical page.)
In my opinion, this is perhaps the strongest argument *for* a separate
"giant page" syscall interface. It will be very hard (perhaps
impossible) to optimize superpages to work efficiently when the ratio
of superpage/basepage grows huge (as, by definition, the kernel would
manage them as a set of basepages). For example, even if we used a
base page-size of 64KB, a 4GB giant page (as supported by Itanium 2)
would correspond to 65536 base pages. A superpage of this size would
almost certainly still do a lot better than 65536 base pages, but
compared to a single giant page, it probably stands no chance
performance-wise.
--david
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