Is maximum swap usage tunable?

[Mike]

On 2/28/2018 4:43 PM, bob prohaska wrote:
> On Wed, Feb 28, 2018 at 02:37:36PM -0500, Mike wrote:
>> On 2/28/2018 1:55 PM, bob prohaska wrote:
>>> On Wed, Feb 28, 2018 at 12:20:56PM -0500, Mike wrote:
>>>> On 2/28/2018 12:03 PM, bob prohaska wrote:
>>>>> In watching system compilations on an RPi3 it looks as if the
>>>>> system starts killing processes with "out of swap" warnings 
>>>>> well below 50% of full utilization (in this case, 2 GB). One
>>>>> recent instance of make -j4 kernel-toolchain killed llvm-tblgen
>>>>> with only 34% of the swap in use.
>>>>>
>>>>> Is the maximum swap usage limit adjustable in any way? I didn't
>>>>> recognize anything useful in the page at
>>>>> https://www.freebsd.org/cgi/man.cgi?query=sysctl(8)&sektion=&manpath=freebsd-release-ports 
>>>>>
>>>>> It's possible the problem is really swap speed, rather than size, so I'd
>>>>> like to try changing size limits if possible. The swap media claims 2-3 
>>>>> MB/sec random write speed and observations with gstat seem to support the
>>>>> claim, but transient stalls are hard to observe. An RPi2 with similar 
>>>>> hardware seems to have no problems.
>>>>>
>>>>
>>>>
>>>>> It's possible the problem is really swap speed
>>>>
>>>> I was running into swap speed / timeout issues.  There were messages on
>>>> the console to that effect.
>>>>
>>>> Once I put the swap space on rotating rust, that part of the compile
>>>> problem disappeared.  I use 1GB swap space.
>>>>
>>>
>>> The latest kernel versions seem to have largely done away with the
>>> "indefinite wait buffobj" warnings. They're few and far between,
>>> the compile proceeds unless they're abundant. The fact that armv7
>>> has no problem, and the system is reporting "out of swap" with 34%
>>> in use strikes me as suspicious. Kernel and userland are in sync, 
>>> so the figure of 34% swap usage is probably accurate. 
>>>
>>> Perhaps my question is better phrased thus: How does FreeBSD-arm 
>>> determine when it's out of swap?
>>>
>>
>>
>> Thanks for the follow-up.
>>
>> I was planning to download and try the
>>
>>   RPI3-20180226-r330034
>>
>> image file this evening.  Per your comment, I'll not use the rusty swap
>> space, and see what happens.
>>
>> I'll report back, probably on the morrow...
>>
> FWIW, I've been using Sandisk Extreme USB 3 flash drives for
> /usr /var/ and swap on the Pi3. It seems that flash write 
> speed is a tighter bottleneck than USB 2.0 ports on the Pi.
> Attempts to use older, slower USB 2 flash drives on a Pi2
> didn't work, though the symptoms were never "out of swap".
> 

buildworld is still running.  I started it around 3PM (EST) on March 1.

I'm seeing a lot of swap messages on the console.  The text is:

  swap_pager: indefinite wait buffer: bufobj: 0,
     blkno: [varies], size: [varies]