|author||Eric Wong <firstname.lastname@example.org>||2016-11-28 23:50:10 +0000|
|committer||Eric Wong <email@example.com>||2016-11-28 23:50:10 +0000|
This probably applies to other kernels, too, but I'm most familiar with Linux.
1 files changed, 19 insertions, 1 deletions
@@ -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 it is 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.