Hi Linus, On Mon, Apr 5, 2010 at 11:32 PM, Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> wrote: >> AFAIK, most modern GCs split memory in young and old generation >> "zones" and _copy_ surviving objects from the former to the latter if >> their lifetime exceeds some threshold. The JVM keeps scanning the >> smaller young generation very aggressively which causes TLB pressure >> and scans the larger old generation less often. > > .. my only input to this is: numbers talk, bullsh*t walks. > > I'm not interested in micro-benchmarks, either. I can show infinite TLB > walk improvement in a microbenchmark. > > In order for me to be interested in any complex hugetlb crap, I want real > numbers from real applications. Not "it takes this many cycles to walk a > page table", or "it could matter under these circumstances". > > I also want those real numbers _not_ directly after a clean reboot, but > after running other real loads on the machine that have actually used up > all the memory and filled it with things like dentry data etc. The "right > after boot" case is totally pointless, since a huge part of hugetlb > entries is the ability to allocate those physically contiguous and > well-aligned regions. > > Until then, it's just extra complexity for no actual gain. > > Oh, and while I'm at it, I want a pony too. Unfortunately I wasn't able to find a pony on Google but here are some huge page numbers if you're interested: http://zzzoot.blogspot.com/2009/02/java-mysql-increased-performance-with.html I'm actually bit surprised you find the issue controversial, Linus. I am not a real JVM hacker (although I could probably play one on TV) but the "hugepages are a big win" argument seems pretty logical for any GC heavy activity. Wouldn't be the first time I was wrong, though. Pekka -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxxx For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>