Re: SwapOnZRAM and how it affects earlyoom thresholds

[Igor Raits]

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On Tue, 2020-07-14 at 01:28 +0900, Alexey A. wrote:
>  > The most
>  > common value I've found over a long period of time, for swap
>  > without
>  > hibernation is 50% of RAM.
>  
>  With low RAM (2G) it's easy to use swap on zram with disksize = 150%
>  MemTotal with opening browsers.
>  
>  50% maybe OK with MemTotal=8G.
>  
>  > I'd like to hear from Alexey what he thinks about further reducing
>  > the
>  > values in earlyoom versus possibly raising the cap in
>  > zram-generator-defaults.
>  
>  It may be OK to reduce mem cap to 200 MiB. This threshold also can
>  work
>  well and may be sufficient to prevent freezing.
>  
>  I would suggest to increase zram disksize caps up to 75% and maybe to
>  6GB. 
Please open ticket upstream with some more details, please.

>  пт, 10 июл. 2020 г. в 01:19, Chris Murphy
> <lists(a)colorremedies.com&gt;:
>  
>  > On Thu, Jul 9, 2020 at 9:49 AM Rex Dieter <rdieter(a)math.unl.edu&gt;
>  > wrote:
>  > > 
>  > > part of some irc discussions on
>  > > https://fedoraproject.org/wiki/Changes/KDEEarlyOOM
>  > > 
>  > > raised my attention to related item,
>  > > https://fedoraproject.org/wiki/Changes/SwapOnZRAM
>  > > 
>  > > As it stands currently with earlyoom, it's default thresholds are
>  > > 4% ram
>  > and
>  > > 10% swap before it acts.  That's fine and dandy.
>  > > 
>  > > Upon reading the SwapOnZRAM feature proposal, I see it is
>  > > advocating
>  > > allocating 50% of ram for swap.  I'd like folks to consider and
>  > > evaluate
>  > how
>  > > this impacts earlyoom.  It effectively makes the earlyoom memory
>  > threshold
>  > > double (right?).  If so, at least think about lowering 4 to (2 or
>  > > 3),
>  > since
>  > > that will make earlyoom's behavior closer to before swaponzram
>  > > was
>  > > introduced.
>  > > 
>  > > Thoughts?
>  > 
>  > The net effect is that earlyoom is more likely to trigger than with
>  > a
>  > disk based swap because right now disk based swap is huge by
>  > default.
>  > It's huge by default to accommodate a hibernation image. The most
>  > common value I've found over a long period of time, for swap
>  > without
>  > hibernation is 50% of RAM. So this approximates those expectations.
>  > 
>  > I'd like to hear from Alexey what he thinks about further reducing
>  > the
>  > values in earlyoom versus possibly raising the cap in
>  > zram-generator-defaults. I don't want to get too carried away
>  > there,
>  > because we are applying this to upgrades (wherever the to-be-
>  > obsoleted
>  > 'zram' package exists already even if not enabled). There is an
>  > opportunity, of course, right now and through beta testing, to keep
>  > on
>  > testing variations on both the size of the zram device used for
>  > swap
>  > and for earlyoom. But we also have another Fedora release, Fedora
>  > 34.
>  > So I'm more inclined to go conservative so long as that itself
>  > isn't
>  > causing problems.
>  > 
>  > One thing I'm a bit skeptical of with reducing earlyoom's triggers
>  > is
>  > that free memory is needed for the recovery from an actual kill.
>  > Usually this is just sigterm. That's the first attempt. If that
>  > doesn't work then earlyoom issues sigkill, which is at a lower
>  > threshold already.
>  > 
>  > 
>  > --
>  > Chris Murphy
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- -- 
Igor Raits <ignatenkobrain(a)fedoraproject.org&gt;
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