RPI3 swap experiments

[Mark Millard]

On 2018-Jul-17, at 11:06 PM, bob prohaska <fbsd at www.zefox.net> wrote:

> 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.

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.

> In this case swap was split, 2 each 1GB  partitions on USB flash plus 1 GB on the 
> 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.

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.

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).

> Details are at
> http://www.zefox.net/~fbsd/rpi3/swaptests/r336356/2gbusbflash_1gbsdflash/


===
Mark Millard
marklmi at yahoo.com
( dsl-only.net went
away in early 2018-Mar)