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Re: kern/55166: uvm_pdpolicy_clock params (anon/exec/file max/min)defaults
The following reply was made to PR kern/55166; it has been noted by GNATS.
From: Joerg Sonnenberger <joerg%bec.de@localhost>
Cc: kern-bug-people%netbsd.org@localhost, gnats-admin%netbsd.org@localhost,
Subject: Re: kern/55166: uvm_pdpolicy_clock params (anon/exec/file
Date: Mon, 13 Apr 2020 19:55:11 +0200
On Mon, Apr 13, 2020 at 03:30:04PM +0000, Izumi Tsutsui wrote:
> The following reply was made to PR kern/55166; it has been noted by GNATS.
> From: Izumi Tsutsui <tsutsui%ceres.dti.ne.jp@localhost>
> To: gnats-bugs%netbsd.org@localhost
> Cc: joerg%bec.de@localhost, tsutsui%ceres.dti.ne.jp@localhost
> Subject: Re: kern/55166: uvm_pdpolicy_clock params (anon/exec/file max/min)defaults
> Date: Tue, 14 Apr 2020 00:29:16 +0900
> joerg@ wrote:
> > > There parameters can be changed by sysctl(8), but initial values
> > > are hardcorded in uvmpdpol_init():
> > What about actually tuning the initial parameters on the amount of RAM
> > in the system? That seems much more sensible than hard-coding different
> > option sets in various kernels. It's not like it is going to add a lot
> > of (cold) code.
> I'm afraid we don't have reasonable fomula to determine optimized
> parameters per the amount of RAM. IIRC, there were several discussion
> about the default value ("current filemax was too large" etc.) just
> after UBC was introduced, but I didn't see any conclusion.
> My suggestion (making the initial parameters configurable) is just
> an intermediate fix.
Sure, we are quite bad at auto-tuning based on avalable memory in
general. That doesn't mean we shouldn't try. We don't have to go for
perfect here either. Pick a reasonable size for boosting exec
specifically should be enough.
> > filemax seems questionable to me, the rest sound a useful default for
> > systems with <= 16MB RAM.
> I guess the default BUFCACHE (vm.bufcache / vm.bufmem, 15% of RAM) is
> enough and no extra file cache is necessary for less memory systems.
But the buffer cache is only used for meta-data, not for regular
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