Date: Sat, 4 Jan 2025 12:36:20 -0500 From: Karl Denninger <karl@denninger.net> To: freebsd-hackers@freebsd.org Subject: Re: curious crashes when under memory pressure Message-ID: <33db3282-25c4-42fb-8d97-1918d52fa9e2@denninger.net> In-Reply-To: <9e71d8eb-74c3-4bcb-89b1-90d4f9746168@quip.cz> References: <CAPx1GvfwqFqvMm0RkTvxa4BJStvOdG0=pNx2dCuWEzCXsqhqHw@mail.gmail.com> <slrnvnij2h.26bu.pmc@disp.intra.daemon.contact> <CAPx1GvfOh4g1AeOcYXC26W5jbPAgA_E_t7CW9chg4miC8c15-w@mail.gmail.com> <9e71d8eb-74c3-4bcb-89b1-90d4f9746168@quip.cz>
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From: Karl Denninger <karl@denninger.net>
To: freebsd-hackers@freebsd.org
Message-ID: <33db3282-25c4-42fb-8d97-1918d52fa9e2@denninger.net>
Subject: Re: curious crashes when under memory pressure
References: <CAPx1GvfwqFqvMm0RkTvxa4BJStvOdG0=pNx2dCuWEzCXsqhqHw@mail.gmail.com>
<slrnvnij2h.26bu.pmc@disp.intra.daemon.contact>
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<9e71d8eb-74c3-4bcb-89b1-90d4f9746168@quip.cz>
In-Reply-To: <9e71d8eb-74c3-4bcb-89b1-90d4f9746168@quip.cz>
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<p><br>
</p>
<div class=3D"moz-cite-prefix">On 1/4/2025 12:30, Miroslav Lachman
wrote:<br>
</div>
<blockquote type=3D"cite"
cite=3D"mid:9e71d8eb-74c3-4bcb-89b1-90d4f9746168@quip.cz">On
04/01/2025 17:27, Chris Torek wrote:
<br>
<blockquote type=3D"cite">On Sat, Jan 4, 2025 at 7:01=E2=80=AFAM Pe=
ter 'PMc'
Much
<br>
<a class=3D"moz-txt-link-rfc2396E" href=3D"mailto:pmc@citylink.di=
noex.sub.org"><pmc@citylink.dinoex.sub.org></a> wrote:
<br>
<blockquote type=3D"cite">
<blockquote type=3D"cite">I'm swapping to a zfs mirror
<br>
</blockquote>
<br>
Well, You shouldn't do that.
<br>
</blockquote>
<br>
Why not? Swapping to a *file* on zfs has obvious issues, but
swapping
<br>
to a mirrored swap partition seems like it should be entirely
safe. A
<br>
bit slow (double writes) but I spent $ on RAM rather than M.2
drives
<br>
on the theory that I can add those later as needed.
<br>
</blockquote>
<br>
Do you have swap on ZFS or not (in the first post you said
"swapping to a zfs mirror")? If yes then it can cause the problems
in memory pressure because system has no free memory but ZFS needs
memory.
<br>
If you want the swap on a mirror, then use separate partition on 2
disks and add gmirror on top of them.
<br>
<br>
Kind regards
<br>
Miroslav Lachman
<br>
<br>
</blockquote>
<p>What's the argument for swapping to a mirror in the first place?=C2=
=A0
If the issue is throughput IMHO the answer is to swap to multiple
devices.</p>
<p>Putting swap through a filesystem abstraction as noted above runs
the risk of requiring an allocation of RAM for the operation to
complete when you're desperately short on it in the first place
resulting in serious trouble.<br>
</p>
<div class=3D"moz-signature">-- <br>
Karl Denninger<br>
<a href=3D"mailto:karl@denninger.net" class=3D"moz-txt-link-freetex=
t">karl@denninger.net</a><br>
<i>The Market Ticker</i><br>
<font size=3D"-2"><i>[S/MIME encrypted email preferred]</i></font><=
/div>
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