OpenZFS: kldload zfs.ko freezes on i386 4GB memory

[Cy Schubert]

In message <CAPrugNoYZS4wcyrpQ0584jZM1zTnwds7rCQPtm5ahJ8Gm91H1A at mail.gmail.c
om>
, Matthew Macy writes:
> On Fri, Oct 30, 2020 at 4:50 PM Cy Schubert <Cy.Schubert at cschubert.com> wrote
> :
> >
> > In message <20201030233138.GD34923 at zxy.spb.ru>, Slawa Olhovchenkov writes:
> > > On Fri, Oct 30, 2020 at 04:00:55PM -0700, Cy Schubert wrote:
> > >
> > > > > > > More stresses memory usually refers to performance penalty.
> > > > > > > Usually way for better performance is reduce memory access.
> > > > > >
> > > > > > The reason filesystems (UFS, ZFS, EXT4, etc.) cache is to avoid dis
> k
> > > > > > accesses. Nanoseconds vs milliseconds.
> > > > >
> > > > > I mean compared ZoL ZFS ARC vs old (BSD/Opensolaris/Illumos) ZFS ARC.
> > > > > Any reaason to rise ARC hit rate in ZoL case?
> > > >
> > > > That's what hit rate is. It's a memory access instead of a disk access.
> > > > That's what you want.
> > >
> > > Is ZoL ARC hit rate rise from FreeBSD ARC hit rate?
> >
> > We don't know that. You should be able to find out by running some tests
> > that would populate your ARC and run the test again. I see that my
> > -DNO_CLEAN buildworlds run faster, when I run them a second or third time
> > after making a minor edit, than they did before. Thus I assume it uses
> > memory more efficiently. By default it stores more metadata in ARC, 75%
> > instead of IIRC 25% by default.
> >
> > Getting back to your original question. A more efficient ARC would exercise
> > your memory more intensely because you are replacing disk reads with memory
> > reads. And as I said before the old ZFS "found" weak RAM on three separate
> > occasions in three different machines over the last ten years. You're
> > advised to replace the marginal memory.
>
> Ryan has been able to reproduce this in a VM with 4GB, similarly a VM
> with 2GB loads just fine. It would seem that 4GB triggers a bug in
> limit handling. We're hoping that we can simply lower one of the
> default limits on i386 and make the problem go away.
>
> Please don't shoot the messenger when I observe that, generally
> speaking, i386 is considered a self supported platform due to ZFS
> general inability to perform well with limited memory or KVA. Long
> mode has been available on virtually all processors shipped since
> 2006.

Yes, I was able to use ZFS on a 2 GB Pentium-M (i386) laptop for many 
years. ZFS worked well with a little tuning on such a small machine. Last 
time I booted it was late last year or early this year. It's in a drawer 
right now. I'll try to pull it out this coming week to test it out.

Serendipitous that I was thinking about pulling out that old laptop to test 
out the new ZFS just last week.


-- 
Cheers,
Cy Schubert <Cy.Schubert at cschubert.com>
FreeBSD UNIX:  <cy at FreeBSD.org>   Web:  https://FreeBSD.org
NTP:           <cy at nwtime.org>    Web:  https://nwtime.org

	The need of the many outweighs the greed of the few.