mm/mm_init.c: not always search next deferred_init_pfn from very beginning

In function deferred_init_memmap(), we call
deferred_init_mem_pfn_range_in_zone() to get the next deferred_init_pfn.
But we always search it from the very beginning.

Since we save the index in i, we can leverage this to search from i next
time.

[rppt refine the comment]
Signed-off-by: Wei Yang <richard.weiyang@gmail.com>
Link: https://lore.kernel.org/all/20240605071339.15330-1-richard.weiyang@gmail.comSigned-off-by: Mike Rapoport (IBM) <rppt@kernel.org>

include/linux/memblock.h

@@ -299,25 +299,6 @@ void __next_mem_pfn_range(int *idx, int nid, unsigned long *out_start_pfn,
 void __next_mem_pfn_range_in_zone(u64 *idx, struct zone *zone,
 				  unsigned long *out_spfn,
 				  unsigned long *out_epfn);
-/**
- * for_each_free_mem_pfn_range_in_zone - iterate through zone specific free
- * memblock areas
- * @i: u64 used as loop variable
- * @zone: zone in which all of the memory blocks reside
- * @p_start: ptr to phys_addr_t for start address of the range, can be %NULL
- * @p_end: ptr to phys_addr_t for end address of the range, can be %NULL
- *
- * Walks over free (memory && !reserved) areas of memblock in a specific
- * zone. Available once memblock and an empty zone is initialized. The main
- * assumption is that the zone start, end, and pgdat have been associated.
- * This way we can use the zone to determine NUMA node, and if a given part
- * of the memblock is valid for the zone.
- */
-#define for_each_free_mem_pfn_range_in_zone(i, zone, p_start, p_end)	\
-	for (i = 0,							\
-	     __next_mem_pfn_range_in_zone(&i, zone, p_start, p_end);	\
-	     i != U64_MAX;					\
-	     __next_mem_pfn_range_in_zone(&i, zone, p_start, p_end))
 
 /**
  * for_each_free_mem_pfn_range_in_zone_from - iterate through zone specific

mm/mm_init.c

@@ -2021,24 +2021,29 @@ static unsigned long  __init deferred_init_pages(struct zone *zone,
 }
 
 /*
- * This function is meant to pre-load the iterator for the zone init.
- * Specifically it walks through the ranges until we are caught up to the
- * first_init_pfn value and exits there. If we never encounter the value we
- * return false indicating there are no valid ranges left.
+ * This function is meant to pre-load the iterator for the zone init from
+ * a given point.
+ * Specifically it walks through the ranges starting with initial index
+ * passed to it until we are caught up to the first_init_pfn value and
+ * exits there. If we never encounter the value we return false indicating
+ * there are no valid ranges left.
  */
 static bool __init
 deferred_init_mem_pfn_range_in_zone(u64 *i, struct zone *zone,
 				    unsigned long *spfn, unsigned long *epfn,
 				    unsigned long first_init_pfn)
 {
-	u64 j;
+	u64 j = *i;
+
+	if (j == 0)
+		__next_mem_pfn_range_in_zone(&j, zone, spfn, epfn);
 
 	/*
 	 * Start out by walking through the ranges in this zone that have
 	 * already been initialized. We don't need to do anything with them
 	 * so we just need to flush them out of the system.
 	 */
-	for_each_free_mem_pfn_range_in_zone(j, zone, spfn, epfn) {
+	for_each_free_mem_pfn_range_in_zone_from(j, zone, spfn, epfn) {
 		if (*epfn <= first_init_pfn)
 			continue;
 		if (*spfn < first_init_pfn)
@@ -2110,7 +2115,7 @@ deferred_init_memmap_chunk(unsigned long start_pfn, unsigned long end_pfn,
 {
 	unsigned long spfn, epfn;
 	struct zone *zone = arg;
-	u64 i;
+	u64 i = 0;
 
 	deferred_init_mem_pfn_range_in_zone(&i, zone, &spfn, &epfn, start_pfn);
 
@@ -2141,7 +2146,7 @@ static int __init deferred_init_memmap(void *data)
 	unsigned long start = jiffies;
 	struct zone *zone;
 	int max_threads;
-	u64 i;
+	u64 i = 0;
 
 	/* Bind memory initialisation thread to a local node if possible */
 	if (!cpumask_empty(cpumask))
@@ -2216,7 +2221,7 @@ bool __init deferred_grow_zone(struct zone *zone, unsigned int order)
 	unsigned long first_deferred_pfn = pgdat->first_deferred_pfn;
 	unsigned long spfn, epfn, flags;
 	unsigned long nr_pages = 0;
-	u64 i;
+	u64 i = 0;
 
 	/* Only the last zone may have deferred pages */
 	if (zone_end_pfn(zone) != pgdat_end_pfn(pgdat))