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[107.215.223.229]) by smtp.gmail.com with ESMTPSA id n8-20020a170902e54800b001b03f208323sm12926328plf.64.2023.12.14.14.06.34 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 14 Dec 2023 14:06:34 -0800 (PST) Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable From: Bakul Shah Mime-Version: 1.0 (1.0) Date: Thu, 14 Dec 2023 14:06:23 -0800 Message-Id: References: <20231214214805.81B2618C08F@mercury.lcs.mit.edu> In-Reply-To: <20231214214805.81B2618C08F@mercury.lcs.mit.edu> To: jnc@mercury.lcs.mit.edu X-Mailer: iPad Mail (20H232) Message-ID-Hash: 2DNCDDPPMABG46AHFGYPONK2E6OCBMWA X-Message-ID-Hash: 2DNCDDPPMABG46AHFGYPONK2E6OCBMWA X-MailFrom: bakul@iitbombay.org X-Mailman-Rule-Misses: dmarc-mitigation; no-senders; approved; emergency; loop; banned-address; member-moderation; nonmember-moderation; administrivia; implicit-dest; max-recipients; max-size; news-moderation; no-subject; digests; suspicious-header CC: coff@tuhs.org X-Mailman-Version: 3.3.6b1 Precedence: list Subject: [COFF] Re: Terminology query - 'system process'? List-Id: Computer Old Farts Forum Archived-At: List-Archive: List-Help: List-Owner: List-Post: List-Subscribe: List-Unsubscribe: I remember calling them kernel processes as they had no code running in user= mode. Not sure now of the year but sometime in =E2=80=9880s. Now I=E2=80=99= d probably call them kernel threads as they don=E2=80=99t have a separate ad= dress space. > On Dec 14, 2023, at 1:48 PM, jnc@mercury.lcs.mit.edu wrote: >=20 > =EF=BB=BFSo Lars Brinkhoff and I were chatting about daemons: >=20 > https://gunkies.org/wiki/Talk:Daemon >=20 > 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 a= re > daemon-like, but are fundamentally different in major ways (explained late= r > 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?) >=20 >=20 > Early UNIX is one of the first systems to have one (process 0, the "schedu= ling (swapping) > process"), but the CACM "The UNIX Time-Sharing System" paper: >=20 > https://people.eecs.berkeley.edu/~brewer/cs262/unix.pdf >=20 > 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": >=20 > http://roguelife.org/~fujita/COOKIES/HISTORY/3BSD/design.pdf >=20 > where it is called the "pageout daemon".("During system initialization, ju= st > 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 bein= g > 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 ter= m > 'daemon' for them. >=20 >=20 > 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). >=20 > 'System processes' do none of these things: their object code is linked in= to > 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 routi= nes > directly; they run in kernel mode, using the same memory mapping as the > kernel itself; etc, etc. >=20 > Another important point is that system processes are highly intertwined wi= th > the operation of the kernel; without the system process(es) operating > correctly, the operation of the system will quickly grind to a halt. The l= oss > of ordinary' daemons is usually not fatal; if the email daemon dies, the > system will keep running indefinitely. Not so, for the swapping process, o= r > the pageout daemon >=20 >=20 > Anyway, is there a standard term for these things? If not, a better name t= han > 'system process'? >=20 > Noel