I'm rebuilding my kernel, and thought I'd go ahead and add 64 gig support even though I only have 4G of memory, just for growth. Do I lose anything by doing that, in performance or anything else?

TIA!
anw

I seem to remember reading something about a 1-3% loss in processing with bigmem. But, that's probably on a machine that's fully loaded 100% of the time. As a practical matter, you shouldn't notice anything.

You need the "64G" level of memory support (AKA "PAE") just to get more than three point something GB of usable ram.

So if you have 4GB of ram, you won't have use of all of it unless you select the 64 gig support.

PAE adds a tiny bit of work for the kernel when mapping memory and a tiny bit of work for the CPU during TLB misses, but usually those things add up to nothing measurable. (64 bit mode adds more to both those things than PAE does and still usually isn't a measurable difference).

Some workloads could see a performance loss of a few percent, but those aren't very likely.

If your system can use 3.5GB or less without PAE and nearly a full 4GB with PAE, and you do significant file I/O, it is more likely to get a few percent performance improvement from the extra caching you get from the extra ram than it is to lose a few percent from the PAE overhead. But in an ordinary home system, I don't think you'll notice the performance difference in either direction.

Thanks, guys! I'll go for it.