On 04/02/20 at 10:01am, Michal Hocko wrote:

On Wed 01-04-20 10:51:55, Mike Rapoport wrote:

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Hi,

On Wed, Apr 01, 2020 at 01:42:27PM +0800, Baoquan He wrote:

[...]

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From above information, we can remove HAVE_MEMBLOCK_NODE_MAP, and
replace it with CONFIG_NUMA. That sounds more sensible to store nid into
memblock when NUMA support is enabled.

 
Replacing CONFIG_HAVE_MEMBLOCK_NODE_MAP with CONFIG_NUMA will work, but
this will not help cleaning up the whole node/zone initialization mess and
we'll be stuck with two implementations.

Yeah, this is far from optimal.

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The overhead of enabling HAVE_MEMBLOCK_NODE_MAP is only for init time as
most architectures will anyway discard the entire memblock, so having it in
a UMA arch won't be a problem. The only exception is arm that uses
memblock for pfn_valid(), here we may also think about a solution to
compensate the addition of nid to the memblock structures. 

Well, we can make memblock_region->nid defined only for CONFIG_NUMA.
memblock_get_region_node would then unconditionally return 0 on UMA.
Essentially the same way we do NUMA for other MM code. I only see few
direct usage of region->nid.

Checked code again, seems HAVE_MEMBLOCK_NODE_MAP is selected directly in
all ARCHes which support it. Means HAVE_MEMBLOCK_NODE_MAP is enabled by
default on those ARCHes, and has no dependency on CONFIG_NUMA at all.
E.g on x86, it just calls free_area_init_nodes() in generic code path,
while free_area_init_nodes() is defined in CONFIG_HAVE_MEMBLOCK_NODE_MAP
ifdeffery scope. So I tend to agree with Mike to remove
HAVE_MEMBLOCK_NODE_MAP firstly on all ARCHes. We can check if it's worth
only defining memblock_region->nid for CONFIG_NUMA case after
HAVE_MEMBLOCK_NODE_MAP is removed.

config X86
        def_bool y
	...
	select HAVE_MEMBLOCK_NODE_MAP
	...