From: Peter Chubb <peterc@xxxxxxxxxxxxxxxxxx> Date: Wed, 26 Mar 2008 10:41:32 +1100 > It's actually harder than it looks. Ian Wienand just finished his > Master's project in this area, so we have *lots* of data. The main > issue is that, at least on Itanium, you have to turn off the hardware > page table walker for hugepages if you want to mix superpages and > standard pages in the same region. (The long format VHPT isn't the > panacea we'd like it to be because the hash function it uses depends > on the page size). This means that although you have fewer TLB misses > with larger pages, the cost of those TLB misses is three to four times > higher than with the standard pages. If the hugepage is more than 3 to 4 times larger than the base page size, which it almost certainly is, it's still an enormous win. > Other architectures (where the page size isn't tied into the hash > function, so the hardware walked can be used for superpages) will have > different tradeoffs. Right, admittedly this is just a (one of many) strange IA64 quirk. -- To unsubscribe from this list: send the line "unsubscribe linux-ia64" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
|