Re: cache sync ioctl, freezes

[Manuel Bouyer <bouyer%antioche.eu.org@localhost>]

On Fri, Nov 01, 2024 at 08:36:07PM -0400, Greg Troxel wrote:
> [...]
> 
> Things are mostly ok, except:
> 
>   - I get spurious DIOCCACHESYNC failed messages (below).  I think
>     that's because zvols don't support cache sync.  I don't know if this
>     is harmless or not.

25 is ENOTTY, which indeed would point to zpool not supporting DIOCCACHESYNC.
This cause a reliability problem; if the dom0 crash you may end up with
a corruped domU filesystem (especially is using -o log).

I've never seen these DIOCCACHESYNC messages with file-backed domUs.

> 
>   - If I run the system out of ram (by mallocing 8GB in a system with
>     6GB of RAM, and then writing to each page), the system freezes, by
>     which I mean an ssh session stops responding to CR and if I do e.g
>        echo 204500; date
>     typing that at 204500, then the date printed is usually 2 minutes
>     plus later.  (This happens without zfs loaded!)

Yes, I also noticed that when the system runs out of ram+swap it usually
requires a hard reset (seen it on bare metal with a too high MAKE_JOBS).
No Xen or ZFS involved here.

-- 
Manuel Bouyer <bouyer%antioche.eu.org@localhost>
     NetBSD: 26 ans d'experience feront toujours la difference
--