Date: Wed, 18 Jul 2018 12:35:38 -0700 From: Mark Millard <marklmi@yahoo.com> To: bob prohaska <fbsd@www.zefox.net> Cc: freebsd-arm <freebsd-arm@freebsd.org>, Trev <freebsd-arm@sentry.org> Subject: Re: RPI3 swap experiments Message-ID: <2CFAE691-3176-4E8C-8542-6D66BE4421A6@yahoo.com> In-Reply-To: <20180718190951.GB27481@www.zefox.net> References: <20180629233937.GC35717@www.zefox.net> <0f137e06-214a-3e8c-a216-f061ec04ac2c@sentry.org> <20180630005145.GA43801@www.zefox.net> <6f3406e2-71f3-d0c2-2b65-703e1a1d3c25@sentry.org> <8e92b2b7-da61-3efb-7231-9fac76b2c1d4@sentry.org> <ba33d8a7-a849-3893-8016-0765ebe1c51f@sentry.org> <2deaaec3-f78f-0b09-5ca7-27e14c6979f9@sentry.org> <20180704004554.GA61273@www.zefox.net> <20180718060650.GA24566@www.zefox.net> <F31DD1B5-42A8-4A48-A771-D38479604FD5@yahoo.com> <20180718190951.GB27481@www.zefox.net>
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On 2018-Jul-18, at 12:09 PM, bob prohaska <fbsd at www.zefox.net> wrote: > On Wed, Jul 18, 2018 at 07:42:13AM -0700, Mark Millard wrote: >>=20 >>=20 >> On 2018-Jul-17, at 11:06 PM, bob prohaska <fbsd at www.zefox.net> = wrote: >>=20 >>> It appears that some progress has been made in getting swap working = reasonably >>> on the RPI3. A -j4 buildworld attempt running r336356 to compile = 336431 failed >>> with "out of swap" but the worst read and write delays were less = than 5 seconds, >>> a marked improvement over previous examples. >>=20 >> Attributing the time variations that have been observed mostly to = FreeBSD and not >> mostly to the device at issue seems to have little or no evidence to = support it. >>=20 > Possibly a fair objection. This test is with a USB3.0 flash drive. = I'll repeat soon > as possible with a USB3.1 device, which in the past reported much = greater (15 second) > delays. >=20 >>> In this case swap was split, 2 each 1GB partitions on USB flash = plus 1 GB on the=20 >>> microSD card. Previous attempts using 3 each 1 GB partitions on USB = flash have been >>> repeatedly successful, while a single attempt using 3 each 1GB = partitions on microSD >>> failed. >>=20 >> The more swap partitions (or space?) not on a /dev/mmcsd0s* the less = of the >> activity that /dev/mmcsd0 handles and likely the more time it tends = to have >> between explicit operations to do internal housekeeping before the = next >> explicit operation. >>=20 >> So the better approximation to not using /dev/mmcsd0 at all might not = be >> all that much of a surprise at having less of a problem on the device >> (or a problem less often). >>=20 > In earlier tests (same card type) putting _all_ swap on microSD (along = with /tmp)=20 > avoided OOMA kills. Dependable mischief seems to come when swap is on = both microSD=20 > and USB. As I do not know what all is going on for Out Of Memory kills, I was = only directly talking of the likes of ms/w and/or ms/r time figures being = large sometimes. OOMA may have other issues contributing to some of its = activity for all I know. Is a difference, for example, 2 GB total swap vs. 3 GB total swap and = the message about the swap configuration? The memory tracking swap can = fragment and be a source of not being able to use swap as I understand. (I've = quoted the man page material in the past in these exchanges.) Large swap spaces can hit such fragmentation issues sooner. (So there is a tradeoff in having more swap than needed as the amount-more increases.) Trev has reported: "I have run the -j4 buildworld now 11 times using a = single 2G partition". I wonder what would happen for him if he used two 1 GB partitions or three about 2/3 GB byte partitions. The contrasting case = of a working environment changed to have multiple partitions (with the same = total) could indicate something about if multiple partitions are sufficient to = lead to problems (ms/w, ms/r, OOM killing, or some combination). > It's understood that USB and Ethernet share I/O hardware, but I = thought microSD=20 > was at least somewhat independent. Is this wrong? >=20 This I do not know. =3D=3D=3D Mark Millard marklmi at yahoo.com ( dsl-only.net went away in early 2018-Mar)
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