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Date:      Sat, 06 Oct 2018 07:59:57 +0000
From:      bugzilla-noreply@freebsd.org
To:        bugs@FreeBSD.org
Subject:   [Bug 229764] Default settings allow system to wire all ram
Message-ID:  <bug-229764-227-9MoxdAEhqU@https.bugs.freebsd.org/bugzilla/>
In-Reply-To: <bug-229764-227@https.bugs.freebsd.org/bugzilla/>
References:  <bug-229764-227@https.bugs.freebsd.org/bugzilla/>

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https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=3D229764

--- Comment #2 from Shane <FreeBSD@ShaneWare.Biz> ---
(In reply to Andriy Gapon from comment #1)

I'm not looking to change anything as memory is being allocated, I'm only
looking at the sysctl settings, specifically arc_max being limited. Initial=
ly
the default settings but also when assigning a new value. Currently we have
defaults and allow assigning values that let a system get into a non-respon=
sive
state.

On a machine with 8GB of physical RAM, max_wired is 2.4GB and arc_max is 7G=
B -
that's RAM minus 1GB, so out of the box an 8GB system is allowed to wire mo=
re
than 9GB, well maybe not allowed but two unrelated areas assuming they can
allocate. I know from experience that a system with 8GB that has over 7GB w=
ired
only responds to the reset button. In this configuration, I expect sysctl
should prevent arc_max being more than 5GB.

If max_wired is only user wired allocations, then kernel wiring is another
factor to be added into the equation.

So initally, as max_wired is 30% of RAM, the default arc_max should not be =
set
higher than 70% of RAM. When sysctl assigns a new value to arc_max the phys=
ical
RAM and max_wired (and kernel wiring?) should be considered to check if the=
 new
value would allow the total wired RAM to be too high.

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