Re: [PATCH v9 02/12] mm/sparsemem: Add helpers track active portions of a section at boot

[Oscar Salvador]

On Wed, Jun 05, 2019 at 02:57:59PM -0700, Dan Williams wrote:
> Prepare for hot{plug,remove} of sub-ranges of a section by tracking a
> sub-section active bitmask, each bit representing a PMD_SIZE span of the
> architecture's memory hotplug section size.
> 
> The implications of a partially populated section is that pfn_valid()
> needs to go beyond a valid_section() check and read the sub-section
> active ranges from the bitmask. The expectation is that the bitmask
> (subsection_map) fits in the same cacheline as the valid_section() data,
> so the incremental performance overhead to pfn_valid() should be
> negligible.
> 
> Cc: Michal Hocko <mhocko@xxxxxxxx>
> Cc: Vlastimil Babka <vbabka@xxxxxxx>
> Cc: Logan Gunthorpe <logang@xxxxxxxxxxxx>
> Cc: Oscar Salvador <osalvador@xxxxxxx>
> Cc: Pavel Tatashin <pasha.tatashin@xxxxxxxxxx>
> Tested-by: Jane Chu <jane.chu@xxxxxxxxxx>
> Signed-off-by: Dan Williams <dan.j.williams@xxxxxxxxx>

Reviewed-by: Oscar Salvador <osalvador@xxxxxxx>

-- 
Oscar Salvador
SUSE L3