RPI3 swap experiments

[Trev]

Trev wrote on 04/07/2018 07:09:
> Conclusion: The only way to buildworld on the RPi3B+ is to use an 
> external USB mechanical hard disk (my hybrid Seagate 500G 2.5" drive 
> required a powered USB hub). No issues on a RPi2B v1.1 with swap and 
> /usr on a USB memory key.

One last experiment occurred to me: I placed a SanDisk 8GB Ultra micro 
SDCard in a microSD card reader (this one: 
https://www.amazon.co.uk/MICRO-SD-MICRO-SDHC-MEMORY-READER/dp/B002WKD0CQ 
), created a 2G swap partition and ran make -j4 buildworld SUCCESSFULLY! 
Twice.

uname -aKUp
FreeBSD rpi3.sentry.org 12.0-CURRENT FreeBSD 12.0-CURRENT #0 r335854: 
Mon Jul  2 16:03:04 AEST 2018 
root at rpi3.sentry.org:/usr/obj/usr/src/arm64.aarch64/sys/RPI3-12.0  arm64 
aarch64 1200069 1200069


gpart show -l da0
=>      40  15523760  da0  GPT  (7.4G)
         40   4194304    1  usdswap  (2.0G)
    4194344  11329456       - free -  (5.4G)


# Custom /etc/fstab for FreeBSD embedded images
/dev/ufs/rootfs   /       ufs     rw,noatime      1       1
/dev/msdosfs/MSDOSBOOT /boot/msdos msdosfs rw,noatime 0 0
md1 /tmp mfs rw,noatime,-s100m 0 0
md2 /var/log mfs rw,noatime,-s15m 0 0
md3 /var/tmp mfs rw,noatime,-s15m 0 0
/dev/da0p1      none    swap    sw      0       0


da0 at umass-sim0 bus 0 scbus0 target 0 lun 0
da0: <SD/MMC Card  Reader 1.00> Removable Direct Access SCSI device
da0: Serial Number 058F63356432
da0: 40.000MB/s transfers
da0: 7580MB (15523840 512 byte sectors)
da0: quirks=0x2<NO_6_BYTE>


The only unusual, but apparently harmless, log messages were:

Jul  7 15:39:01 rpi3 kernel: swap_pager: indefinite wait buffer: bufobj: 
0, blkno: 143089, size: 327
68
Jul  7 17:46:35 rpi3 kernel: swap_pager: indefinite wait buffer: bufobj: 
0, blkno: 14712, size: 8192
Jul  7 17:47:21 rpi3 kernel: swap_pager: indefinite wait buffer: bufobj: 
0, blkno: 17239, size: 2457
6
Jul  7 17:47:21 rpi3 kernel: swap_pager: indefinite wait buffer: bufobj: 
0, blkno: 20737, size: 8192
Jul  7 17:47:21 rpi3 kernel: swap_pager: indefinite wait buffer: bufobj: 
0, blkno: 511807, size: 409
6
Jul  7 18:50:34 rpi3 kernel: swap_pager: indefinite wait buffer: bufobj: 
0, blkno: 988, size: 4096
Jul  7 18:50:34 rpi3 kernel: swap_pager: indefinite wait buffer: bufobj: 
0, blkno: 318727, size: 655
36
Jul  7 18:55:02 rpi3 kernel: swap_pager: indefinite wait buffer: bufobj: 
0, blkno: 354041, size: 286
72
Jul  7 21:45:10 rpi3 kernel: swap_pager: indefinite wait buffer: bufobj: 
0, blkno: 164496, size: 491
52
Jul  7 23:04:38 rpi3 kernel: swap_pager: indefinite wait buffer: bufobj: 
0, blkno: 372151, size: 655
36