Re: ZFS + FreeBSD XEN dom0 panic

On 2022.04.12. 18:37, Roger Pau Monné wrote:
> 
> I have a patch to disable the bounce buffering done in blkback
> (attached).

Regarding this patch, it wouldn't apply on RELEASE 13.0 code, because i 
guess there are other changes, when updating code manually i got compile 
error, variable xen_cpuid_base not defined, and include paths do not 
have <contrib> at the start.

So i applied it manually to main branch, commit: 
2f0baec1ecb2e79cfb97a19e1bbfb27741365847, since there at least variable 
xen_cpuid_base existed.


> While I think it's not directly related to the panic you are hitting,
> it's long time since we should have disabled that.  It should reduce
> the memory consumption by blkback greatly, so might have the side
> effect of helping with your issue related to pmap_growkernel.

I think i do not understand this clearly. Was it an obsolete feature 
that had to be removed?


> On my test box a single instance of blkback reduced memory usage from
> ~100M to ~300K.

On my lab system this seems to work quiet niceley as well. System is 
under load now for 17:36 hours, no panic, collecting vmstat. And what 
else is different, that VM start/stop script has not printed any error 
about adding block devices.

So this seems promissing.