[PATCH 5/7] mm: move zone iterator outside of deferred_init_maxorder()

[Daniel Jordan]

padata will soon divide up pfn ranges between threads when parallelizing
deferred init, and deferred_init_maxorder() complicates that by using an
opaque index in addition to start and end pfns.  Move the index outside
the function to make splitting the job easier, and simplify the code
while at it.

deferred_init_maxorder() now always iterates within a single pfn range
instead of potentially multiple ranges, and advances start_pfn to the
end of that range instead of the max-order block so partial pfn ranges
in the block aren't skipped in a later iteration.  The section alignment
check in deferred_grow_zone() is removed as well since this alignment is
no longer guaranteed.  It's not clear what value the alignment provided
originally.

Signed-off-by: Daniel Jordan <daniel.m.jordan@xxxxxxxxxx>
---
 mm/page_alloc.c | 88 +++++++++++++++----------------------------------
 1 file changed, 27 insertions(+), 61 deletions(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 68669d3a5a665..990514d8f0d94 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -1708,55 +1708,23 @@ deferred_init_mem_pfn_range_in_zone(u64 *i, struct zone *zone,
 }
 
 /*
- * Initialize and free pages. We do it in two loops: first we initialize
- * struct page, then free to buddy allocator, because while we are
- * freeing pages we can access pages that are ahead (computing buddy
- * page in __free_one_page()).
- *
- * In order to try and keep some memory in the cache we have the loop
- * broken along max page order boundaries. This way we will not cause
- * any issues with the buddy page computation.
+ * Initialize the struct pages and then free them to the buddy allocator at
+ * most a max order block at a time because while we are freeing pages we can
+ * access pages that are ahead (computing buddy page in __free_one_page()).
+ * It's also cache friendly.
  */
 static unsigned long __init
-deferred_init_maxorder(u64 *i, struct zone *zone, unsigned long *start_pfn,
-		       unsigned long *end_pfn)
+deferred_init_maxorder(struct zone *zone, unsigned long *start_pfn,
+		       unsigned long end_pfn)
 {
-	unsigned long mo_pfn = ALIGN(*start_pfn + 1, MAX_ORDER_NR_PAGES);
-	unsigned long spfn = *start_pfn, epfn = *end_pfn;
-	unsigned long nr_pages = 0;
-	u64 j = *i;
-
-	/* First we loop through and initialize the page values */
-	for_each_free_mem_pfn_range_in_zone_from(j, zone, start_pfn, end_pfn) {
-		unsigned long t;
-
-		if (mo_pfn <= *start_pfn)
-			break;
-
-		t = min(mo_pfn, *end_pfn);
-		nr_pages += deferred_init_pages(zone, *start_pfn, t);
-
-		if (mo_pfn < *end_pfn) {
-			*start_pfn = mo_pfn;
-			break;
-		}
-	}
-
-	/* Reset values and now loop through freeing pages as needed */
-	swap(j, *i);
-
-	for_each_free_mem_pfn_range_in_zone_from(j, zone, &spfn, &epfn) {
-		unsigned long t;
-
-		if (mo_pfn <= spfn)
-			break;
+	unsigned long nr_pages, pfn;
 
-		t = min(mo_pfn, epfn);
-		deferred_free_pages(spfn, t);
+	pfn = ALIGN(*start_pfn + 1, MAX_ORDER_NR_PAGES);
+	pfn = min(pfn, end_pfn);
 
-		if (mo_pfn <= epfn)
-			break;
-	}
+	nr_pages = deferred_init_pages(zone, *start_pfn, pfn);
+	deferred_free_pages(*start_pfn, pfn);
+	*start_pfn = pfn;
 
 	return nr_pages;
 }
@@ -1814,9 +1782,11 @@ static int __init deferred_init_memmap(void *data)
 	 * that we can avoid introducing any issues with the buddy
 	 * allocator.
 	 */
-	while (spfn < epfn) {
-		nr_pages += deferred_init_maxorder(&i, zone, &spfn, &epfn);
-		cond_resched();
+	for_each_free_mem_pfn_range_in_zone_from(i, zone, &spfn, &epfn) {
+		while (spfn < epfn) {
+			nr_pages += deferred_init_maxorder(zone, &spfn, epfn);
+			cond_resched();
+		}
 	}
 zone_empty:
 	/* Sanity check that the next zone really is unpopulated */
@@ -1883,22 +1853,18 @@ deferred_grow_zone(struct zone *zone, unsigned int order)
 	 * that we can avoid introducing any issues with the buddy
 	 * allocator.
 	 */
-	while (spfn < epfn) {
-		/* update our first deferred PFN for this section */
-		first_deferred_pfn = spfn;
-
-		nr_pages += deferred_init_maxorder(&i, zone, &spfn, &epfn);
-		touch_nmi_watchdog();
-
-		/* We should only stop along section boundaries */
-		if ((first_deferred_pfn ^ spfn) < PAGES_PER_SECTION)
-			continue;
-
-		/* If our quota has been met we can stop here */
-		if (nr_pages >= nr_pages_needed)
-			break;
+	for_each_free_mem_pfn_range_in_zone_from(i, zone, &spfn, &epfn) {
+		while (spfn < epfn) {
+			nr_pages += deferred_init_maxorder(zone, &spfn, epfn);
+			touch_nmi_watchdog();
+
+			/* If our quota has been met we can stop here */
+			if (nr_pages >= nr_pages_needed)
+				goto out;
+		}
 	}
 
+out:
 	pgdat->first_deferred_pfn = spfn;
 	pgdat_resize_unlock(pgdat, &flags);
 
-- 
2.26.2