GPT vs MBR for swap devices

Mark Millard marklmi at
Sat Jun 16 23:13:26 UTC 2018

bob prohaska fbsd at wrote on
Sat Jun 16 19:12:22 UTC 2018 (some by reference
to other web pages, which is what I quote from
here) :

> Presently, the divided swap layout fails during -j4 buildworld with
> "out of swap" kills during the more frantic portions of buildworld.
> When all swap is placed on a single 3 GB USB mechanical disk partition
> the "out of swap" errors go away. Similarly, when swap is placed entirely
> on the microSD card in two partitions, one the original 1 GB partition 
> plus a second 2 GB partition, the "out of swap" errors dissapear.

Since the "multiple swap partitions across multiple
devices" context (my description) is what has problems,
it would be interesting to see swapinfo information
from around the time frame of the failures: how much is
used vs. available on each swap partition? Is only one
being (significantly) used? The small one (1 GiByte)?

A related, additional example to try? . . .

Since you report needing around 1.2 GiByte of swap, what
happens if you have a split but both devices have, say,
1.5 GiByte of swap space for the partition used? If I read
right, you could shrink the 2GiByte microSD card partition
and the 3 GiByte USB mechanical disk partition and then use
that pair as a test. (This also avoids the message about
having too much swap. Also, I'm avoiding having significant
size differences between the partitions used.) Technically,
without the split, either partition should be sufficient
without the other involved. In such a context, does the
split still fail? Or does it only fail when one partition
is stoo small to be sufficient by itself?

These suggestions are going a different direction than the
I/O rate investigation but also having I/O rate information
would not hurt. But I/O rate information can not substitute
for the swapinfo output here. Nor can top cover what I'd be
looking for: per partition usage figures are required, not
just grand total swap-space usage.

Mark Millard
marklmi at
( went
away in early 2018-Mar)

More information about the freebsd-arm mailing list