®The LuaJIT GC64 Mode
OpenResty® uses LuaJIT for its main computing engine, and
users
mainly use the Lua programming language to write applications atop OpenResty,
sometimes very complex ones. For years, there has been a notorious hard
limit in the maximum memory size managed by LuaJIT’s garbage collector
(GC). This limit was 2 GB on 64-bit systems (including x86_64). Fortunately,
since 2016, the official LuaJIT[1] has introduced a new build mode
called “GC64”, which raises this limit to 128 TB (or the low 47-bit address
space). Effectively, this translates to no limit for almost all the PCs
and servers in the
market nowadays. Over the two years, the GC64 mode has matured enough and
starting from the OpenResty 1.15.8.1 release,
we enable this
by default on the x86_64 architectures, just like the ARM64 (or AArch64)
architecture. This article will provide an overview of the old memory limit
as well as an explanation of the new GC64 mode.