GPT vs MBR for swap devices

Thu Jun 21 14:51:57 UTC 2018

[When I send to Trev, my Email is rejected as spam. This happens
even for a direct send without the list address or other addresses
involved. I do not see evidence of why in what I get back in the
"unable to deliver" notice. The below is just a resend with this
note added: no new technical content.]

On 2018-Jun-21, at 7:16 AM, Mark Millard <marklmi at yahoo.com> wrote:

> On 2018-Jun-21, at 12:28 AM, Trev <freebsd-arm at sentry.org> wrote:
> 
>> I gave in and bought an Raspberry Pi 3B+ and now I've been bitten by Bob's OOM assassin too...
>> 
>> % gpart show
>> =>      63  31116225  mmcsd0  MBR  (15G)
>>       63      2016          - free -  (1.0M)
>>     2079    102312       1  fat32lba  [active]  (50M)
>>   104391  31008825       2  freebsd  (15G)
>> 31113216      3072          - free -  (1.5M)
>> 
>> =>       0  31008825  mmcsd0s2  BSD  (15G)
>>        0        57            - free -  (29K)
>>       57  31008768         1  freebsd-ufs  (15G)
>> 
>> =>      40  60567472  da0  GPT  (29G)
>>       40   4194304    1  freebsd-swap  (2.0G)
>>  4194344  56373168    2  freebsd-ufs  (27G)
>> 
>> % cat /etc/fstab
>> # 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/ufs/swap   none    swap    sw      0       0
>> /dev/ufs/usr    /usr    ufs     rw,noatime      2       2
>> 
>> da0 is a brand new 32G EMTEC USB2 memory key housing /usr and swap partitions.
>> 
>> FreeBSD 12.0-CURRENT #0 r335317: Mon Jun 18 17:37:04 UTC 2018 root at releng3.nyi.freebsd.org:/usr/obj/usr/src/arm64.aarch64/sys/GENERIC arm64
>> 
>> make -j4 buildworld resulted in:
>> 
>> Jun 21 17:05:12 rpi3 kernel: pid 10326 (c++), uid 0, was killed: out of swap space
>> --- CodeGen/AsmPrinter/CodeViewDebug.o ---
>> c++: error: unable to execute command: Killed
>> c++: error: clang frontend command failed due to signal (use -v to see invocation)
>> FreeBSD clang version 6.0.0 (tags/RELEASE_600/final 326565) (based on LLVM 6.0.0)
>> Target: aarch64-unknown-freebsd12.0
>> Thread model: posix
>> InstalledDir: /usr/bin
>> c++: note: diagnostic msg: PLEASE submit a bug report to https://bugs.freebsd.org/submit/ and include the crash backtrace, preprocessed source, and associated run script.
>> c++: note: diagnostic msg:
>> 
>> I happened to have been watching top (5 second interval) at the time and of the 2G swap, only 45M was shown to be in use.
> 
> Are you getting errors such as those listed in:
> 
> https://lists.freebsd.org/pipermail/freebsd-arm/2018-June/018091.html
> 
> ? If not, your context may be a better test case than Bob P.'s.
> 
> It looks like the latest from Bob P. is that when his /dev/da0
> is not used for swap (and so has far less I/O) his builds finish,
> apparently without logging errors:
> 
> http://www.zefox.net/~fbsd/rpi3/swaptests/newtests/1gbsdflash_1.3gbusbmechanical_swapinfo/readme
> 
> where he writes:
> 
>> This test used the 1 GB SD flash swap partition plus a 1.3 GB partition 
>> on a USB mechanical disk. The -j4 buildworld ran to completion without
>> obvious errors, serving mostly to suggest there's nothing wrong with 
>> the read/write behavior of /dev/da0, the USB flash drive holding /usr
>> and with it /usr/obj.
> 
> 
> (I do not share his conclusion about /dev/da0 based on the smaller
> amount of I/O when it was not used for swapping.)
> 
> As far as I know the swap system is far more dependent on timely
> I/O than the other I/O involved in a build.
> 
> Even without errors considered Bob was getting things like the
> large ms/w figures below:
> 
>> Mon Jun 18 09:42:05 PDT 2018
>> Device          1K-blocks     Used    Avail Capacity
>> /dev/da0b         1048576     3412  1045164     0%
>> /dev/mmcsd0s3b    1048576     3508  1045068     0%
>> Total             2097152     6920  2090232     0%
>> dT: 10.043s  w: 10.000s
>> L(q)  ops/s    r/s   kBps   ms/r    w/s   kBps   ms/w    d/s   kBps   ms/d   %busy Name
>>   0      0      0      0    0.0      0      9   10.8      0      0    0.0    0.1  mmcsd0
>>  46      0      0      0    0.0      0     16  12355      0      0    0.0   85.9  da0
>>   0      0      0      0    0.0      0      9   10.8      0      0    0.0    0.1  mmcsd0s3
>>   0      0      0      0    0.0      0      9   10.8      0      0    0.0    0.1  mmcsd0s3a
>>  33      0      0      0    0.0      0     22  12318      0      0    0.0  114.1  da0d
>> Mon Jun 18 09:42:25 PDT 2018
>> Device          1K-blocks     Used    Avail Capacity
>> /dev/da0b         1048576     3412  1045164     0%
>> /dev/mmcsd0s3b    1048576     3508  1045068     0%
>> Total             2097152     6920  2090232     0%
> 
> 
> Are you getting such during the swapping activity?
> 
> Overall: the I/O errors (if any) and the large ms/w (or ms/r) figures
> are things to look for.

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