[TUHS] signals and blocked in I/O

Warner Losh imp at bsdimp.com
Tue Dec 5 03:19:19 AEST 2017

On Mon, Dec 4, 2017 at 9:36 AM, <arnold at skeeve.com> wrote:

> Larry McVoy <lm at mcvoy.com> wrote:
> > So I have 10 processes, they all run until the system starts to
> > thrash, then they are all in wait mode for memory but there isn't
> > any (and there is no swap configured).
> Um, pardon me for asking the obvious question, but why not just configure
> a few gigs of swap to give the OS some breathing room?
> Most modern systems let you use a regular old file in the filesystem
> for swap space, instead of having to repartition your disk and using a
> dedicated partition. I'd be suprised if your *BSD box didn't let you do
> that too.  It's a little slower, but a gazillion times more convenient.

The deployed systems in the field have swap space configured. But if we're
not careful we can still run out. Larry's tests are at the extreme limits,
to be sure, and not having swap exacerbates the bad behavior at the limit.
If he's trying to ameliorate bad effects, doing it on worst case scenario
certainly helps. The BSD box allows for it, and it's not that much slower,
but it kinda misses the point of the exercise.

Also, the systems in questions often operate at the limits of the disk
subsystem, so additional write traffic is undesirable. They are also SSDs,
so doubly undesirable where avoidable.

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