RPI3 swap experiments

[Mark Millard]

On 2018-Jul-30, at 11:44 PM, Mark Millard <marklmi at yahoo.com> wrote:

> On 2018-Jul-30, at 10:47 PM, bob prohaska <fbsd at www.zefox.net> wrote:
> 
>> OOMA is still killing processes in -j4 buildworld sessions for no obvious reason
>> when using mixed USB/microSD swap.  The most recent experiment is with r336877 
>> rebuilding itself from a clean start.
>> 
>> The various log files are at 
>> http://www.zefox.net/~fbsd/rpi3/swaptests/r336877/
>> The OOMA kills occur around two hours after
>> the worst read/write delays, which are in the low tens
>> of seconds. Perhaps most curiously, the long delays
>> don't appear to involve swap partitions. 
>> 
>> Similar problems now seem present with the RPI2 on
>> 11-stable. The first failure was with r335398 trying 
>> to compile 336871. Buildworld has been backed down to 
>> -j2 and restarted in the hope it'll eventually succeed.
>> In this particular case all swap is on USB, in a single
>> 2 GB partition.
> 
> My records indicate (from old boot messages and reported
> in past list messages):
> 
> rpi2: . . . exceeds maximum recommended amount (411488 pages).
> rpi3: . . . exceeds maximum recommended amount (925680 pages).
> 
> 411488*4K Bytes = 1,685,454,848 Bytes for rpi2 (older V1.1 armv7
> variant). In other words: you have more swap than is recommended
> for such a context because of fragmentation issues and such for
> overhead information related to keeping track of swapping/paging.
> 
> I suggest trying not exceeding the 1,685,454,848 figure for the
> rpi2 context, just as a cross check. May be 411000*4K Bytes,
> so 1,683,456,000 Bytes, avoiding being right at the boundary?
> 
> 925680*4K Bytes = 3,791,585,280 Bytes for rpi3.
> 
> Are thew drives involved different ones than used with the
> rpi3 experiments? (Just curious.)
> 
> 
>> It would be most interesting to see what happens if OOMA
>> could be turned off. Is that possible? 
> 
> If the code reaches conditions which initiate OOMA now, what
> would proposed alternate action be? As stands if OOMA itself
> fails to happen, my guess would be the kernel would panic,
> deadlock, or livelock in some way. Simply having OOMA not
> attempted would likely be the same as OOMA failing unless
> more than disabling OOMA was done.
> 
> (I'm no expert at such so if someone that knows makes a claim,
> believe them instead of me.)

Looking around, there have been other rpi2 figures that I've
seen and reported on the lists, for example:

exceeds maximum recommended amount (405460 pages)
exceeds maximum recommended amount (469280 pages)

So if you do not have a specific figure from a boot message,
your might want:

400000*4K Bytes = 1,638,400,000 Bytes

or even somewhat less. If you have a specific figure from a
current boot message for the same version, I'd go somewhat
less than that figure scaled to Bytes.


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