Date: Mon, 13 Aug 2018 11:53:50 -0700 From: bob prohaska <fbsd@www.zefox.net> To: Mark Millard <marklmi@yahoo.com> Cc: Mark Johnston <markj@FreeBSD.org>, John Kennedy <warlock@phouka.net>, freebsd-arm <freebsd-arm@freebsd.org>, bob prohaska <fbsd@www.zefox.net> Subject: Re: RPI3 swap experiments ["was killed: out of swap space" with: "v_free_count: 5439, v_inactive_count: 1"] Message-ID: <20180813185350.GA47132@www.zefox.net> In-Reply-To: <FC0798A1-C805-4096-9EB1-15E3F854F729@yahoo.com> References: <20180808204841.GA19379@raichu> <2DC1A479-92A0-48E6-9245-3FF5CFD89DEF@yahoo.com> <20180809033735.GJ30738@phouka1.phouka.net> <20180809175802.GA32974@www.zefox.net> <20180812173248.GA81324@phouka1.phouka.net> <20180812224021.GA46372@www.zefox.net> <B81E53A9-459E-4489-883B-24175B87D049@yahoo.com> <20180813021226.GA46750@www.zefox.net> <0D8B9A29-DD95-4FA3-8F7D-4B85A3BB54D7@yahoo.com> <FC0798A1-C805-4096-9EB1-15E3F854F729@yahoo.com>
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On Mon, Aug 13, 2018 at 10:35:38AM -0700, Mark Millard wrote: > On 2018-Aug-12, at 8:36 PM, Mark Millard <marklmi at yahoo.com> wrote: > > > On 2018-Aug-12, at 7:12 PM, bob prohaska <fbsd at www.zefox.net> wrote: > > > >> . . . > >> Would 1024 be enough to turn OOMA off completely? That's what I originally wanted to > >> try. > > > > [The 1024 is for vm.pageout_oom_seq.] > > I'm going to try a different wording about vm.pageout_oom_seq > to address such questions: > > vm.pageout_oom_seq indirectly sets how long FreeBSD will tolerate > Low Free RAM (by its Low Free RAM criteria). The "indirect" is > because my wording is time based but the vm.pageout_oom_seq units > are not. For a given environment smaller vs. larger is less time > vs. more time. > > So, while one can make FreeBSD tolerate Low Free RAM longer > (up to a point, apparently huge), no specific value directly > turns off OOM (better: Low Free RAM) process killing. (Based on > mathematical arithmetic. I've not analyze odd consequences of > causing overflows for the code's details.) > > The approximation to turning off being intolerant of Low Free > RAM is to have vm.pageout_oom_seq so large that you would not > be willing to wait for the process kills to start. > > But the minimum for that is likely not obvious, so just use > a fairly large figure for the int value for the architecture > being tested. (rpi2 V1.1's and rpi3's have fairly large int > types in C.) > > (I've assumed that the representation of vm.pageout_oom_seq is > respected everywhere that it is used. If someplace mixes it > with smaller types, this would need to be considered for what > is "fairly large". This would require a code inspection.) > I'll start with 1024 as "almost" ten times 120 and see what happens. Thank you very much for explaining in plain English what vm.pageout_oom_seq influences. I had no idea it was tied to free RAM, taking the reference to swap literally. I can't resist asking two dumb questions: First, why the confusing wording of the error message, is it shared with other tests? Second, wouldn't it be better to suppress the starting of new processes, rather than killing those already underway? Sort of like a harried clerk saying "take a number!". Another approach might be to write an entire process space to /tmp for restart when the crisis is over. Lousy for throughput, but it would keep folks away from the power switch. Many thanks! bob prohaska
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