[COFF] Re: Terminology query - 'system process'?

On Dec 14, 2023, at 1:48 PM, jnc(a)mercury.lcs.mit.edu wrote: So Lars Brinkhoff and I were chatting about daemons: https://gunkies.org/wiki/Talk:Daemon and I pointed out that in addition to 'standard' daemons (e.g. the printer spooler daemon, email daemon, etc, etc) there are some other things that are daemon-like, but are fundamentally different in major ways (explained later below). I dubbed them 'system processes', but I'm wondering if ayone knows if there is a standard term for them? (Or, failing that, if they have a suggestion for a better name?) Early UNIX is one of the first systems to have one (process 0, the "scheduling (swapping) process"), but the CACM "The UNIX Time-Sharing System" paper: https://people.eecs.berkeley.edu/~brewer/cs262/unix.pdf doesn't even mention it, so no guidance there. Berkeley UNIX also has one, mentioned in "Design and Implementation of the Berkeley Virtual Memory Extensions to the UNIX Operating System": http://roguelife.org/~fujita/COOKIES/HISTORY/3BSD/design.pdf where it is called the "pageout daemon".("During system initialization, just before the init process is created, the bootstrapping code creates process 2 which is known as the pageout daemon. It is this process that .. writ[es] back modified pages. The process leaves its normal dormant state upon being waken up due to the memory free list size dropping below an upper threshold.") However, I think there are good reasons to dis-favour the term 'daemon' for them. For one thing, typical daemons look (to the kernel) just like 'normal' processes: their object code is kept in a file, and is loaded into the daemon's process when it starts, using the same mechanism that 'normal' processes use for loading their code; daemons are often started long after the kernel itself is started, and there is usually not a special mechanism in the kernel to start daemons (on early UNIXes, /etc/rc is run by the 'init' process, not the kernel); daemons interact with the kernel through system calls, just like 'ordinary' processes; the daemon's process runs in 'user' CPU mode (using the same standard memory mapping mechanisms, just like blah-blah). 'System processes' do none of these things: their object code is linked into the monolithic kernel, and is thus loaded by the bootstrap; the kernel contains special provision for starting the system process, which start as the kernel is starting; they don't do system calls, just call kernel routines directly; they run in kernel mode, using the same memory mapping as the kernel itself; etc, etc. Another important point is that system processes are highly intertwined with the operation of the kernel; without the system process(es) operating correctly, the operation of the system will quickly grind to a halt. The loss of ordinary' daemons is usually not fatal; if the email daemon dies, the system will keep running indefinitely. Not so, for the swapping process, or the pageout daemon Anyway, is there a standard term for these things? If not, a better name than 'system process'? Noel