[TUHS] VM over-commit (and the OOM killers)

At Thu, 27 Feb 2025 17:55:49 -0500, Henry Bent <henry.r.bent(a)gmail.com> wrote: Subject: [TUHS] Re: Having dickens of a time compiling gcc-4.4.7 on tru64 . I'm pretty sure over-commit in virtual memory systems is older than linux, and of course it's common in the BSDs now too. Windows-NT did it, as did early AIX. IBM'S VM does it, as do many other virtual machine supervisors. Unix System V may even have done it. I don't know where it originated, and I couldn't find a quick reference online just now to give a history of it, but likely someone here does. AIX also had an "OOM" killer (but I think it was the paging system itself, no a user-level process) -- which in early releases (the first version 3 on RS/6000 in 1989 or 1990) just tromped on the biggest process, which was usually the Xserver. I seem to remember the system rebooting if X died too. Even earlier (for the RT) IBM had invented SIGDANGER to warn of a pending OOM condition. Big users of memory could catch SIGDANGER and know they had to release some memory if they could. I think catchers of SIGDANGER would avoid the early SIGKILLs too, but I don't believe the Xserver tried to catch SIGDANGER, at least not in early releases. Some systems, e.g. macOS (nee OS X) somewhat solved the problem by simply adding more swap space dynamically by creating files in the root filesystem (until the disk fills). -- Greg A. Woods <gwoods(a)acm.org> Kelowna, BC +1 250 762-7675 RoboHack <woods(a)robohack.ca> Planix, Inc. <woods(a)planix.com> Avoncote Farms <woods(a)avoncote.ca>