On 29.2.2016 18:55, Dan Williams wrote: > On Mon, Feb 29, 2016 at 4:33 AM, Vlastimil Babka <[email protected]> wrote: >> On 02/02/2016 06:42 AM, Andrew Morton wrote: >>> So if you want ZONE_DMA, you're limited to 512 NUMA nodes? >>> >>> That seems reasonable. >> >> >> Sorry for the late reply, but it seems that with !SPARSEMEM, or with >> SPARSEMEM_VMEMMAP, reducing NUMA nodes isn't even necessary, because >> SECTIONS_WIDTH is zero (see the diagrams in linux/page-flags-layout.h). In >> my brief tests with 4.4 based kernel with SPARSEMEM_VMEMMAP it seems that >> with 1024 NUMA nodes and 8192 CPU's, there's still 7 bits left (i.e. 6 with >> CONFIG_NR_ZONES_EXTENDED). >> >> With the danger of becoming even more complex, could the limit also depend >> on CONFIG_SPARSEMEM/VMEMMAP to reflect that somehow? > > In this case it's already part of the equation because: > > config ZONE_DEVICE > depends on MEMORY_HOTPLUG > depends on MEMORY_HOTREMOVE > > ...and those in turn depend on SPARSEMEM.
Fine, but then SPARSEMEM_VMEMMAP should be still an available subvariant of SPARSEMEM with SECTION_WIDTH=0.
