Re: DISCONTIGMEM is deprecated

Re: DISCONTIGMEM is deprecated

[Christoph Hellwig]

On Tue, Apr 23, 2019 at 07:49:57PM +0300, Meelis Roos wrote:
> > > ia64 (looks complicated ...)
> > 
> > Well as far as I can tell it was not even used 12 or so years ago on
> > Itanium when I worked on that stuff.
> 
> My notes tell that on UP ia64 (RX2620), !NUMA was broken with both
> SPARSEMEM and DISCONTIGMEM. NUMA+SPARSEMEM or !NUMA worked. Even
> NUMA+DISCONTIGMEM worked, that was my config on 2-CPU RX2660.

ia64 has a such a huge number of memory model choices.  Maybe we
need to cut it down to a small set that actually work.

That includes fund bits like the 'VIRTUAL_MEM_MAP' option where the
comment claims:

# VIRTUAL_MEM_MAP and FLAT_NODE_MEM_MAP are functionally equivalent.
# VIRTUAL_MEM_MAP has been retained for historical reasons.

but it still is selected as the default if sparsemem is not enabled..

RE: DISCONTIGMEM is deprecated

[Luck, Tony]

> ia64 has a such a huge number of memory model choices.  Maybe we
> need to cut it down to a small set that actually work.

SGI systems had extremely discontiguous memory (they used some high
order physical address bits in the tens/hundreds of terabyte range for the
node number ... so there would be a few GBytes of actual memory then
a huge gap before the next node had a few more Gbytes).

I don't know of anyone still booting upstream on an SN2, so if we start doing
serious hack and slash the chances are high that SN2 will be broken (if it isn't
already).

-Tony

Re: DISCONTIGMEM is deprecated

[Christoph Hellwig]

On Mon, Apr 29, 2019 at 04:58:09PM +0000, Luck, Tony wrote:
> > ia64 has a such a huge number of memory model choices.  Maybe we
> > need to cut it down to a small set that actually work.
> 
> SGI systems had extremely discontiguous memory (they used some high
> order physical address bits in the tens/hundreds of terabyte range for the
> node number ... so there would be a few GBytes of actual memory then
> a huge gap before the next node had a few more Gbytes).
> 
> I don't know of anyone still booting upstream on an SN2, so if we start doing
> serious hack and slash the chances are high that SN2 will be broken (if it isn't
> already).

When I wrote this, I thought of

!NUMA:  flat mem
NUMA:	sparsemem
SN2:	discontig

based on Meelis report.  But now that you mention it, I bet SN2 has
already died slow death from bitrot.  It is so different in places, and
it doesn't seem like anyone care - if people want room sized SGI
machines the Origin is much more sexy (hello Thomas!) :)

So maybe it it time to mark SN2 broken and see if anyone screams?

Without SN2 the whole machvec mess could basically go away - the
only real difference between the remaining machvecs is which iommu
if any we set up.

Re: DISCONTIGMEM is deprecated

[Christopher Lameter]

On Mon, 29 Apr 2019, Christoph Hellwig wrote:

> So maybe it it time to mark SN2 broken and see if anyone screams?
>
> Without SN2 the whole machvec mess could basically go away - the
> only real difference between the remaining machvecs is which iommu
> if any we set up.

SPARSEMEM with VMEMMAP was developed to address these
issues and allow one mapping scheme across the different platforms.

You do not need DISCONTIGMEM support for SN2. And as far as I know (from a
decade ago ok....) the distributions were using VMEMMAP instead.