This probably applies to other kernels, too, but I'm most familiar with Linux. --- It took me a while to get the wording below to this point. Maybe there's not enough detail for folks unfamiliar with how OSes work, or maybe there's too much and will be TL;DR-ed...
TUNING | 20 +++++++++++++++++++- 1 file changed, 19 insertions(+), 1 deletion(-) diff --git a/TUNING b/TUNING index 247090b..1f55228 100644 --- a/TUNING +++ b/TUNING @@ -72,10 +72,28 @@ See Unicorn::Configurator for details on the config file format. have them unbuffered (File#sync = true) or they are record(line)-buffered in userspace before any writes. -== Kernel Parameters (Linux sysctl) +== Kernel Parameters (Linux sysctl and sysfs) WARNING: Do not change system parameters unless you know what you're doing! +* Transparent hugepages (THP) improves performance in many cases, + but can also increase memory use when relying on a + copy-on-write(CoW)-friendly GC (Ruby 2.0+) with "preload_app true". + CoW operates at the page level, so writing to a huge page would + trigger a 2 MB copy (x86-64), as opposed to a 4 KB copy on a + regular (non-huge) page. + + Consider only allowing THP to be used when requested via the + madvise(2) syscall: + + echo madvise >/sys/kernel/mm/transparent_hugepage/enabled + + Or disabling it system-wide, via "never". + + n.b. "page" in this context only applies to the OS kernel, + Ruby GC implementations also use this term for the same concept + in a way that is agnostic to the OS. + * net.core.rmem_max and net.core.wmem_max can increase the allowed size of :rcvbuf and :sndbuf respectively. This is mostly only useful for UNIX domain sockets which do not have auto-tuning buffer sizes. -- EW -- unsubscribe: unicorn-public+unsubscr...@bogomips.org archive: https://bogomips.org/unicorn-public/
