Re: mprotect() api overhead.

[Alan Cox]

> 	For x86 system, is there way to specify 4MB page table entry
> 	instead of 4K page table entry when use the mmap() api.  
> 	With 4MB mmap() page table entry, mprotected should take only
> 	8 iterations to change the access bits for 32 MB of share
> 	memory as compare to 8k iterations for 4k page table entries.
> 	Am I corrected on this?

The mainstream kernel has no real support for 4Mb pages - some experimental
work has been done but little else. Even then the TLB flush has a non
trivial overhead. On SMP the effect will be more significant since it
must ensure the other threads on other processors also see updated page 
tables.

Alan