Based on what we've been seeing maintaining Oracle Linux, there are many workloads for which THP results in a ~9-10% performance hit overall on the system, and this includes kernels up through 3.8.13 (which we're using as the baseline for a new kernel in that distro). It has to do with the fact that the memory allocator uses the slowpath almost all the time, rather than a faster path when memory fragmentation is low. It's not that THP is _enabled_ so much that it is _compiled into the kernel at all_; as a result, we're probably going to remove it for the time being, and re-enable it when the allocator is revamped.
However, there is also good reason for choosing madvise as the default. Transparent hugepages *cannot be swapped out*. Read that carefully: when you use them, the allocated memory is always in-core, as if it had been mlock()ed into place. While systems with plenty of memory shouldn't need to worry about this (hell, I run my systems without swap at all!), it's a consideration to keep in mind. Applications for which huge pages may provide proven benefit, but aren't required, should start to adopt MADV_HUGEPAGE as an advisory call; this might include databases, Web browsers, and other data-intensive applications. That way, you don't run the risk of hitting memory walls thanks to a bunch of smaller system processes that just happen to use hugepages because it's set to "always". -- You received this bug notification because you are a member of Kernel Packages, which is subscribed to linux in Ubuntu. https://bugs.launchpad.net/bugs/743688 Title: Transparent HugePages not enabled in 11.04 kernel Status in “linux” package in Ubuntu: Confirmed Bug description: Transparent hugepages, which is a major performance enhancement in the 2.6.38 kernel is not enabled in the 11.04 kernel.: $ cat /etc/issue Ubuntu natty (development branch) \n \l $ grep TRANSPARENT /boot/config-2.6.38-7-server # CONFIG_TRANSPARENT_HUGEPAGE is not set $ grep TRANSPARENT /boot/config-2.6.38-7-generic # CONFIG_TRANSPARENT_HUGEPAGE is not set $ If this is the way 11.04 kernels will be built, it's a bummer. To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/743688/+subscriptions -- Mailing list: https://launchpad.net/~kernel-packages Post to : kernel-packages@lists.launchpad.net Unsubscribe : https://launchpad.net/~kernel-packages More help : https://help.launchpad.net/ListHelp
