centos man page for node_map_pfn_alignment

NODE_MAP_PFN_ALIGNME(9) 				    Memory Management in Linux					   NODE_MAP_PFN_ALIGNME(9)

NAME
       node_map_pfn_alignment - determine the maximum internode alignment

SYNOPSIS
       unsigned long node_map_pfn_alignment(void);

ARGUMENTS
       void
	   no arguments

DESCRIPTION
       This function should be called after node map is populated and sorted. It calculates the maximum power of two alignment which can
       distinguish all the nodes.

       For example, if all nodes are 1GiB and aligned to 1GiB, the return value would indicate 1GiB alignment with (1 << (30 - PAGE_SHIFT)). If
       the nodes are shifted by 256MiB, 256MiB. Note that if only the last node is shifted, 1GiB is enough and this function will indicate so.

       This is used to test whether pfn -> nid mapping of the chosen memory model has fine enough granularity to avoid incorrect mapping for the
       populated node map.

       Returns the determined alignment in pfn's. 0 if there is no alignment requirement (single node).

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Kernel Hackers Manual 3.10					     June 2014						   NODE_MAP_PFN_ALIGNME(9)