Re: [PATCH v3] mm: make expand_downwards symmetrical toexpand_upwards
From: David Rientjes
Date: Wed Apr 20 2011 - 17:34:58 EST
On Wed, 20 Apr 2011, Matthew Wilcox wrote:
> > That part makes me think the best option is to make parisc do
> > CONFIG_NUMA as well regardless of the historical intent was.
>
> But it's not just parisc. It's six other architectures as well, some
> of which aren't even SMP. Does !SMP && NUMA make any kind of sense?
>
It does as long as DISCONTIGMEM is hijacking NUMA abstractions throughout
the code; for example, look at the .config that James is probably using
for testing here:
CONFIG_PA8X00=y
CONFIG_64BIT=y
CONFIG_DISCONTIGMEM=y
CONFIG_NEED_MULTIPLE_NODES=y
CONFIG_NODES_SHIFT=3
and CONFIG_NUMA is not enabled. So we want CONFIG_NODES_SHIFT of 3
(because MAX_PHYSMEM_RANGES is 8) and CONFIG_NEED_MULTIPLE_NODES is
enabled because of DISCONTIGMEM:
#
# Both the NUMA code and DISCONTIGMEM use arrays of pg_data_t's
# to represent different areas of memory. This variable allows
# those dependencies to exist individually.
#
config NEED_MULTIPLE_NODES
def_bool y
depends on DISCONTIGMEM || NUMA
when in reality we should do away with CONFIG_NEED_MULTIPLE_NODES and just
force DISCONTIGMEM to enable CONFIG_NUMA at least for -stable and as a
quick fix for James.
In the long run, we'll probably want to define a lighterweight CONFIG_NUMA
as a layer that CONFIG_DISCONTIGMEM can use for memory range abstractions
and then CONFIG_NUMA is built on top of it to define proximity between
those ranges.
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