swap space issues

[Donald Wilde]

On 6/24/20, Kevin Oberman <rkoberman at gmail.com> wrote:
> On Wed, Jun 24, 2020 at 10:30 PM Greg 'groggy' Lehey <grog at freebsd.org>
> wrote:
>
>> On Wednesday, 24 June 2020 at 20:34:24 -0700, Donald Wilde wrote:
>> > On 6/24/20, Greg 'groggy' Lehey <grog at freebsd.org> wrote:
>> >> On Wednesday, 24 June 2020 at 18:51:04 -0700, Donald Wilde wrote:
>> >>> On 6/24/20, Greg 'groggy' Lehey <grog at freebsd.org> wrote:
>> >>>> On Wednesday, 24 June 2020 at  9:36:23 -0700, Donald Wilde wrote:
>> >>>>> All,
>> >>>>>
>> >>>>> I recently upgraded my 12-STABLE system to the latest, and now my
>> >>>>> swap subsystems aren't working. I deliberately set up a 40GB
>> >>>>> partition for swap, and when I do 'top -t' I am only seeing 7906M
>> >>>>> total.
>> >>>>
>> >>>> That looks suspiciously like the difference from 32 GB.  Could it be
>> >>>> numeric overflow?  And if so, where?  What does pstat -s say?
>> >>>
>> >>> Well, hi Greg! LTNT2!
>> >>
>> >> Indeed.
>> >>
>> >>> pstat -shm:
>> >>>
>> >>> /dev/ada0s1b  65536 (1M blocks), Used: 1.5G, Avail: 63G, Capacity: 2%
>> >>
>> >> Now that's really puzzling.  Why does it say 64 G when you said 40 G,
>> >> and the error from top tends to confirm it?  How big is the partition
>> >> (gpart output)?
>> >
>> > Attached 'gpart list' output
>>
>> FWIW, gpart show would have done the job.  But what I see there is Yet
>> Another swap partition size, 66 GB.   So so far we have various parts
>> reporting 8 GB, 40 GB, 64 GB and 66 GB.
>>
>> > Reduced kern.maxswzone to 9999999. Is it decimal or unlabeled hex?
>>
>> It'll be decimal, but it refers to the number of swblk structures
>> assigned in memory, and after reading the code I'm still not 100% in
>> the clear how this relates to the size of swap, if at all.
>>
>> > 'top' now shows 4597M total swap.
>>
>> ... and 4.6 GB.  5 different sizes.
>>
>> You really shouldn't be relying on top for swap info.  It's a third
>> party program that demonstrably shows incorrect results (though I

I was continuing to reference it because its 'incorrect results' might
flag where we need to see things working. When 'top' shows the right
results, we've fixed the right thing.

>> believe that the maintainer would be very interested to know why and
>> to fix it).  But pstat -s (without any further options) should show
>> what the kernel thinks.

Here's what I see immediately following shutdown -r and boot:

Device          1K-blocks     Used    Avail Capacity
/dev/ada0s1b     67108864        0 67108864     0%

>>
>> >>> What else can I share to help diagnose this?
>> >>
>> >> Background, maybe?  You say that you upgraded your system.  Did you
>> >> change the swap size when you did?  What were swap and RAM sizes
>> >> before and after?
>> >
>> > Meant that I upgraded from 12.1-RELEASE to 12-STABLE. When I
>> > configured the -RELEASE install, I manually messed with the MBR disk
>> > partitions. This is nominally a half-TB HDD which showed up as a total
>> > of 446 G available (IIRC, gpart should show it's actual size). I did
>> > auto partitioning, looked at the sizes, and manually set my partitions
>> > to give me 40G of swap instead of the auto-generated size of 4G.
>>
>> That's really puzzling.  It seems that it gave you much more than you
>> asked for.
>>
>> Try this in single user mode: modify the size of the swap partition to
>> 30 GB.  I haven't used MBR partitions for years now, but I believe
>> that 'bsdlabel -e' will do the trick.  Just shorten the length of the
>> b partition.  You may need to 'mount -u /'.  If you do it right
>> (check!), this won't harm any of the other partitions: it'll just
>> leave 26 GB free between the swap partition and the next partition.

Thanks again, Greg!

>>
> gpart(8) works just fine on MBR drives and partitions/slices and has a much
> friendlier user interface. "gpart resize"  is the command you want.
> --
> Kevin Oberman, Part time kid herder and retired Network Engineer

Thanks, Kevin! My laptop's BIOS is old enough that it balked when I
tried to boot from a GPT setup of 12.1R. One Of These Days I'll fix
that but the MBR works and I needed to move on.

We'll get there! :D
-- 
Don Wilde
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