Linus Torvalds wrote:
PAE is 'make it barely work'. The whole concept is fundamentally flawed, and anybody who runs a 32-bit kernel with 16GB of RAM doesn't even understand *how* flawed and stupid that is.
Don't do it. Upgrade to 64-bit, or live with the fact that IO performance will suck. The fact that it happened to work better under your particular load with one particular IO size is entirely just 'random noise'.
Yeah, the difference between 'we can cache it' and 'we have to do IO' is huge. With a 32-bit kernel, we do IO much earlier now, just to avoid some really nasty situations. That makes you go from the 'can sit in the cache' to the 'do lots of IO' situation. Tough.
Seriously, you can compile yourself a 64-bit kernel and continue to use your 32-bit user-land. And you can complain to whatever distro you used that it didn't do that in the first place. But we're not going to bother with trying to tune PAE for some particular load. It's just not worth it to .anybody