The Linux 3.8 Kernel Can Save A Lot Of RAM

For certain workloads with the Linux 3.8 kernel the physical memory usage is lowered by a significant amount thanks to improvements within this kernel that's presently under development.

Linus Torvalds merged this afternoon Andrew Morton's patch-bomb for the Linux 3.8 merge window that opened earlier this week. When it comes to the miscellaneous VM changes happening for Linux 3.8, there's one item in particular that's worthy of being mentioned.

This merge brings forth zero huge_page support, which as mentioned in the commit message, "Not a performance boost but it an save large amounts of physical memory in some situations." The merge happened with this Git activity.

The zero huge page support for the Linux kernel was introduced by Intel. As said in the original patch series, "During testing I noticed big (up to 2.5 times) memory consumption overhead on some workloads (e.g. ft.A from NPB) if THP is enabled. The main reason for that big difference is lacking zero page in THP case. We have to allocate a real page on read page fault...With thp-never RSS is about 400k, but with thp-always it's 200M. After the patcheset thp-always RSS is 400k too." (THP is Transparent Huge-Pages.)

With Andrew's patch-bomb from today, the only other item worth mentioning is that there have also been improvements to memory hot-plugging. It was discovered that the current Linux state of memory hot-plugging was actually "badly broken", but Fujitsu has begun to fix-up the support.