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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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