Re: DISCONTIGMEM is deprecated

Mel Gorman
2019-04-19T19:16:22Z

On Fri, Apr 19, 2019 at 07:05:21AM -0700, Matthew Wilcox wrote:
> On Fri, Apr 19, 2019 at 10:43:35AM +0100, Mel Gorman wrote:
> > DISCONTIG is essentially deprecated and even parisc plans to move to
> > SPARSEMEM so there is no need to be fancy, this patch simply disables
> > watermark boosting by default on DISCONTIGMEM.
>
> I don't think parisc is the only arch which uses DISCONTIGMEM for !NUMA
> scenarios. Grepping the arch/ directories shows:
>
> alpha (does support NUMA, but also non-NUMA DISCONTIGMEM)
> arc (for supporting more than 1GB of memory)
> ia64 (looks complicated ...)
> m68k (for multiple chunks of memory)
> mips (does support NUMA but also non-NUMA)
> parisc (both NUMA and non-NUMA)
>
> I'm not sure that these architecture maintainers even know that DISCONTIGMEM
> is deprecated. Adding linux-arch to the cc.

Poor wording then -- yes, DISCONTIGMEM is still used but look where it's
used. I find it impossible to believe that any new arch would support
DISCONTIGMEM or that DISCONTIGMEM would be selected when SPARSEMEM is
available.`It's even more insane when you consider that SPARSEMEM can be
extended to support VMEMMAP so that it has similar overhead to FLATMEM
when mapping pfns to struct pages and vice-versa.

--
Mel Gorman
SUSE Labs