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

[Greg A. Woods]

At Fri, 28 Feb 2025 12:09:49 -0500, Dennis Boone <drb at msu.edu> wrote:
Subject: [TUHS] Re: VM over-commit (and the OOM killers)
>
> I was told a few years ago by a smart person I respect that one of the
> reasons Mac laptops were still so poorly endowed with RAM (iirc 8 GB
> max) was because Apple was shipping SSD in them, so the performance hit
> wasn't really noticeable.  One hopes those were sturdy (DWPD) SSDs, but
> barring the marketing decisions (removing ports people want), Apple's
> hardware engineering is usually decent.

That's probably mostly true, but also misguided and ignorant of the
actual behaviour of RAM-starved systems.  I suspect it was policy based
on memory prices at some time in the past, but seemingly hasn't been
re-evaluated for modern workloads more recently.

MacOS has long been OK at handling a little bit of paging, but seems to
get to the state of thrashing far sooner than one would expect it to.  I
find Apple's default memory provisioning to be half as big as it should
be for the real-world uses most people encounter, especially these days
with the bloatware that is modern desktop software (especially browsers!)


On my BSD systems I always allocate lots of swap space (I try for at
least as much as I have RAM, if not more), but I get worried any time I
see any of it used.  As Warner said, it's fine for transient loads, but
if a system starts paging during regular production loads then I have a
big problem.

--
					Greg A. Woods <gwoods at acm.org>

Kelowna, BC     +1 250 762-7675           RoboHack <woods at robohack.ca>
Planix, Inc. <woods at planix.com>     Avoncote Farms <woods at avoncote.ca>
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