mm: kill find_min_pfn_with_active_regions()

find_min_pfn_with_active_regions() is only called from free_area_init(). 
Open-code the PHYS_PFN(memblock_start_of_DRAM()) into free_area_init(),
and kill find_min_pfn_with_active_regions().

Link: https://lkml.kernel.org/r/20220815111017.39341-1-wangkefeng.wang@huawei.comSigned-off-by: Kefeng Wang <wangkefeng.wang@huawei.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

include/linux/mm.h

@@ -2520,7 +2520,6 @@ extern unsigned long absent_pages_in_range(unsigned long start_pfn,
 						unsigned long end_pfn);
 extern void get_pfn_range_for_nid(unsigned int nid,
 			unsigned long *start_pfn, unsigned long *end_pfn);
-extern unsigned long find_min_pfn_with_active_regions(void);
 
 #ifndef CONFIG_NUMA
 static inline int early_pfn_to_nid(unsigned long pfn)

mm/page_alloc.c

@@ -7908,17 +7908,6 @@ unsigned long __init node_map_pfn_alignment(void)
 	return ~accl_mask + 1;
 }
 
-/**
- * find_min_pfn_with_active_regions - Find the minimum PFN registered
- *
- * Return: the minimum PFN based on information provided via
- * memblock_set_node().
- */
-unsigned long __init find_min_pfn_with_active_regions(void)
-{
-	return PHYS_PFN(memblock_start_of_DRAM());
-}
-
 /*
  * early_calculate_totalpages()
  * Sum pages in active regions for movable zone.
@@ -8211,7 +8200,7 @@ void __init free_area_init(unsigned long *max_zone_pfn)
 	memset(arch_zone_highest_possible_pfn, 0,
 				sizeof(arch_zone_highest_possible_pfn));
 
-	start_pfn = find_min_pfn_with_active_regions();
+	start_pfn = PHYS_PFN(memblock_start_of_DRAM());
 	descending = arch_has_descending_max_zone_pfns();
 
 	for (i = 0; i < MAX_NR_ZONES; i++) {