FYI: various 11.0-CURRENT -r293227 (and older) hangs on arm (rpi2): a description of sorts

[Paul Mather]

On Jan 8, 2016, at 12:49 AM, Mark Millard <markmi at dsl-only.net> wrote:

> Top post of a major conclusion:
> 
> I have isolated a working vs. failing context for the hangs issue:
> (Note that everything for world and ports and such is on the SSD root partition in my examples.)
> 
> A) Using a swap file on the root partition as the swap space leads to hangs when the space gets sufficient activity
> 
> vs.
> 
> B) Using a swap partition as the swap space works without hangs
> 
> It is the same SSD as before both ways. (I had to dump, repartition, restore since I'd not provided space for a swap partition earlier.)
> 
> A swap partition on the sdcard as the swap space also works.
> 
> 
> So it appears there is a problem with using swapfiles --at least when they are on otherwise sometimes-also-busy file systems but possibly more generally. (As the SSD has a USB SSD interface to the RPI2, swapfiles do not provide trim support any more than swap partitions would.)
> 
> The SSD is likely noticeably faster in various respects and so may be more of a challenge for swapfile handling in some way (via extra file-system/IO/resource load with less time between various activities), at least on rpi2's.


This meshes with recent experience I have been having with CURRENT on a BeagleBone Black.  I use a swapfile on the SD card (which also hosts all the OS file systems) and the system would regularly lock up, with GEOM complaining on the console about I/O errors to the mmcsd0 device.

In the past, too, I have experienced panics (on all my arm systems) when the system attempts to page in from swap.

For now, on the BeagleBone Black, I have attached an external USB hard drive and am using a swap partition on there to see if it "solves" the swap problem.  The good news is that it hasn't locked up so far.  (Usually, the nightly periodic jobs are enough to provoke the problem.)

It's good to hear, though, that a swap partition on the SD card also works in your testing.  I will try that next.

Cheers,

Paul.