Re: Why preallocate pmd in x86 32-bit PAE?

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William Lee Irwin III wrote:

There may be bigger fish to fry in terms of per-process overhead, if
you're trying to cut that down. The trouble with trying to address
some of those is that there is mutual antagonism between compactness
and expansibility in the process address space layout, so you'll end
up instantiating a lot more than you want barring some sort of provision
for a compact address space layout. Pagetable sharing is a far more
powerful resource scalability method, though it also needs cooperation
in user address space layout to reap its gains.

There are other overheads, of course, though they're more typically
per-something besides processes.


I think Jeremy's question was due to trying to reduce the 32/64-bit differences. Performance-wise, it might add a small amount to user setup time (a typical 32-bit process will need all four, for the main binary, libraries, stack and kernel, respectively) but it is probably not significant (although I'd like to see numbers just in case).

	-hpa

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