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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: Izumi Tsutsui <>
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.
 >  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.
 Izumi Tsutsui

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