GPT vs MBR for swap devices

Warner Losh imp at
Fri Jun 15 04:01:13 UTC 2018

On Thu, Jun 14, 2018, 9:52 PM bob prohaska <fbsd at> wrote:

> On Thu, Jun 14, 2018 at 02:10:21PM -0700, Rodney W. Grimes wrote:
> >
> > It might be interesting to do in order the swapon
> > commands to 1G USB flash, 1G SD flash, 2G SD flash,
> It seems clear that USB flash swap, alone or in any
> combination, fails early in buildworld.

I think that's because USB flash can't swap fast enough to keep up with the
page demand. You might be able to confirm this by looking at the write
rates to the swap portions for the various other media with gstat. I
suspect it's FTL is doing more expensive garbage collection under a swap
work load leading to long pauses from time to time that the VM system
responds to by starting OOM too soon.


1 GB of SD
> flash swap seemed to work consideraby better, but
> even it slowed greatly when 500 MB swap was in use.
> 3 GB of USB mechanical swap seems to work. 3 GB of SD flash
> swap (2 GB plus 1 GB) also seemed to work.
> These tests were not with the same kernel and sources,
> which makes the comparisons rather suspect.
> The machine is now reverting to r334939 using 1 GB + 2 GB of
> SD flash swap. If that succeeds I will then run buildworld
> for each case using the same kernel, world and sources.
> Thanks for reading!
> bob prohaska
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