[cfarm-users] request for tmpfs on gcc220 (was: gcc220 replaced with new hardware)

[Baptiste Jonglez]

Hi,

On 05-11-21, Juan Francisco Cantero Hurtado via cfarm-users wrote:
> On Fri, 05 Nov 2021 11:14:47 +0100
> Ævar Arnfjörð Bjarmason via cfarm-users
> <cfarm-users at lists.tetaneutral.net> wrote:
> > That's great, yes thanks for providing an OpenBSD machine that's this
> > capible, it's not long ago that I'd often not test at all on OpenBSD
> > because there was just some very slow VM'd 1-core box.
> > 
> > Request: Would it be possible to provide a tmpfs on that machine
> > ("man 8 mount_tmpfs" I believe) similar to the /run/user on some
> > linux boxes? Something in the small number of GBs would be more than
> > sufficient.
> 
> tmpfs was disabled long time ago on OpenBSD and is unsupported. The
> closest thing to tmpfs is mfs:

Indeed, the mount_tmpfs man page and command are still there, but it
doesn't work:

  # mount_tmpfs tmpfs /mnt/test
  mount_tmpfs: tmpfs on /mnt/test: Operation not supported

> https://dataswamp.org/~solene/2018-05-08-mfs-tmp.html
> 
> However, the performance is not really great. Also, if you reserve
> space for mfs, it can't be used as normal RAM.

This system has so much memory that it's not a problem to dedicate a
portion of memory to this.

After trying different configuration, it seems that MFS is limited to
around 32 GB of filesytem size:

  # echo "swap /scratch mfs rw,nodev,nosuid,-s=32750m,-m=0 0 0" >> /etc/fstab
  # mount /scratch
  # df -h /stratch
  Filesystem     Size    Used   Avail Capacity  Mounted on
  mfs:82330     31.0G    1.0K   31.0G     0%    /scratch

Specifying a larger size fails with:

  # mount -t mfs -o -s33G,-m0 swap /mnt/test   
  mount_mfs: mmap: Cannot allocate memory

32 GB should be enough already: Ævar, can you give it a try in /scratch/
and see how it goes?  If it works well, we could enable it for /tmp.

Baptiste
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