I am making a kernel(4.4) for 32bit(above i686) processors.
I guess almost 32bit PC has under 4GB RAM, but some PC has more than 4GB RAM.
So I consider about PAE kernel option.
But there is a cost. like below...

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CONFIG_X86_PAE: PAE is required for NX support, and furthermore enables larger swapspace support for non-overcommit purposes. It has the cost of more pagetable lookup overhead, and also consumes more pagetable space per process.
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I can understand roughly.
But I can't feel excatly.
How big are the overhead and the pagetable space?

Page tables take on the order of 1-2% of the size of RAM. Why are you worrying about the overhead of PAE? You have two arms, but maybe you could get by with one. Why not buy shirts with just one sleeve?

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That's the least of concerns with PAE. Linus has ranted against PAE many times - have a read of one such here

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Only by testing on your system can you decide.

I'll guess that you won't be able to find any difference unless your system is under 24 hour loads.

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