https://github.com/openjdk/jdk/blob/3b576ed99d7664ea0fc851e66f9480a6f4638197/src/hotspot/os/posix/os_posix.inline.hpp#L47

Many functions like os::write, os::exit, os::dll_unload, etc, are implemented in various os*.inline.hpp files. This forces many .hpp and .cpp files to explicitly include "runtime/os.inline.hpp".

There's no performance reason to inline these functions. They will make a system call, whose overhead is way bigger than the cost of making an extra function call.

The full list methods moved from os*inline.hpp to os_<platform>.cpp are:

os::dll_unload(void *lib)
os::lseek(int fd, jlong offset, int whence)
os::fsync(int fd)
os::ftruncate(int fd, jlong length)
os::read(int fd, void *buf, unsigned int nBytes)
os::write(int fd, const void *buf, unsigned int nBytes)
os::close(int fd)
os::socket_close(int fd)
os::socket(int domain, int type, int protocol)
os::recv(int fd, char* buf, size_t nBytes, uint flags)
os::send(int fd, char* buf, size_t nBytes, uint flags)
os::raw_send(int fd, char* buf, size_t nBytes, uint flags)
os::connect(int fd, struct sockaddr* him, socklen_t len)
os::get_host_by_name(char* name)
os::exit(int num)