[PATCH v4 4/4] mm/page_alloc: Introduce free_area_init_core_hotplug

[osalvador]

From: Oscar Salvador <osalvador@xxxxxxx>

Currently, whenever a new node is created/re-used from the memhotplug path,
we call free_area_init_node()->free_area_init_core().
But there is some code that we do not really need to run when we are coming
from such path.

free_area_init_core() performs the following actions:

1) Initializes pgdat internals, such as spinlock, waitqueues and more.
2) Account # nr_all_pages and # nr_kernel_pages. These values are used later on
   when creating hash tables.
3) Account number of managed_pages per zone, substracting dma_reserved and memmap pages.
4) Initializes some fields of the zone structure data
5) Calls init_currently_empty_zone to initialize all the freelists
6) Calls memmap_init to initialize all pages belonging to certain zone

When called from memhotplug path, free_area_init_core() only performs actions #1 and #4.

Action #2 is pointless as the zones do not have any pages since either the node was freed,
or we are re-using it, eitherway all zones belonging to this node should have 0 pages.
For the same reason, action #3 results always in manages_pages being 0.

Action #5 and #6 are performed later on when onlining the pages:
 online_pages()->move_pfn_range_to_zone()->init_currently_empty_zone()
 online_pages()->move_pfn_range_to_zone()->memmap_init_zone()

This patch does two things:

First, moves the node/zone initializtion to their own function, so it allows us
to create a small version of free_area_init_core, where we only perform:

1) Initialization of pgdat internals, such as spinlock, waitqueues and more
4) Initialization of some fields of the zone structure data

These two functions are: pgdat_init_internals() and zone_init_internals().

The second thing this patch does, is to introduce free_area_init_core_hotplug(),
the memhotplug version of free_area_init_core():

Currently, we call free_area_init_node() from the memhotplug path.
In there, we set some pgdat's fields, and call calculate_node_totalpages().
calculate_node_totalpages() calculates the # of pages the node has.

Since the node is either new, or we are re-using it, the zones belonging to
this node should not have any pages, so there is no point to calculate this now.

Actually, we re-set these values to 0 later on with the calls to:

reset_node_managed_pages()
reset_node_present_pages()

The # of pages per node and the # of pages per zone will be calculated when
onlining the pages:

online_pages()->move_pfn_range()->move_pfn_range_to_zone()->resize_zone_range()
online_pages()->move_pfn_range()->move_pfn_range_to_zone()->resize_pgdat_range()

Also, since free_area_init_core() will now only get called during early init, let us replace
__paginginit with __init, so its code gets freed up.

Signed-off-by: Oscar Salvador <osalvador@xxxxxxx>
---
 include/linux/mm.h  |  4 +++
 mm/memory_hotplug.c | 16 ++++--------
 mm/page_alloc.c     | 71 ++++++++++++++++++++++++++++++++++++++---------------
 3 files changed, 60 insertions(+), 31 deletions(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 6954ad183159..17bab044c1bc 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -2002,6 +2002,10 @@ extern void free_area_init_node(int nid, unsigned long * zones_size,
 		unsigned long zone_start_pfn, unsigned long *zholes_size);
 extern void free_initmem(void);
 
+#ifdef CONFIG_MEMORY_HOTPLUG
+extern void free_area_init_core_hotplug(int nid);
+#endif
+
 /*
  * Free reserved pages within range [PAGE_ALIGN(start), end & PAGE_MASK)
  * into the buddy system. The freed pages will be poisoned with pattern
diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index 4eb6e824a80c..9eea6e809a4e 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -982,8 +982,6 @@ static void reset_node_present_pages(pg_data_t *pgdat)
 static pg_data_t __ref *hotadd_new_pgdat(int nid, u64 start)
 {
 	struct pglist_data *pgdat;
-	unsigned long zones_size[MAX_NR_ZONES] = {0};
-	unsigned long zholes_size[MAX_NR_ZONES] = {0};
 	unsigned long start_pfn = PFN_DOWN(start);
 
 	pgdat = NODE_DATA(nid);
@@ -1006,8 +1004,11 @@ static pg_data_t __ref *hotadd_new_pgdat(int nid, u64 start)
 
 	/* we can use NODE_DATA(nid) from here */
 
+	pgdat->node_id = nid;
+	pgdat->node_start_pfn = start_pfn;
+
 	/* init node's zones as empty zones, we don't have any present pages.*/
-	free_area_init_node(nid, zones_size, start_pfn, zholes_size);
+	free_area_init_core_hotplug(nid);
 	pgdat->per_cpu_nodestats = alloc_percpu(struct per_cpu_nodestat);
 
 	/*
@@ -1017,18 +1018,11 @@ static pg_data_t __ref *hotadd_new_pgdat(int nid, u64 start)
 	build_all_zonelists(pgdat);
 
 	/*
-	 * zone->managed_pages is set to an approximate value in
-	 * free_area_init_core(), which will cause
-	 * /sys/device/system/node/nodeX/meminfo has wrong data.
-	 * So reset it to 0 before any memory is onlined.
-	 */
-	reset_node_managed_pages(pgdat);
-
-	/*
 	 * When memory is hot-added, all the memory is in offline state. So
 	 * clear all zones' present_pages because they will be updated in
 	 * online_pages() and offline_pages().
 	 */
+	reset_node_managed_pages(pgdat);
 	reset_node_present_pages(pgdat);
 
 	return pgdat;
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 4e84a17a5030..4e386423622a 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -6237,21 +6237,9 @@ static void pgdat_init_kcompactd(struct pglist_data *pgdat)
 static void pgdat_init_kcompactd(struct pglist_data *pgdat) {}
 #endif
 
-/*
- * Set up the zone data structures:
- *   - mark all pages reserved
- *   - mark all memory queues empty
- *   - clear the memory bitmaps
- *
- * NOTE: pgdat should get zeroed by caller.
- */
-static void __paginginit free_area_init_core(struct pglist_data *pgdat)
+static void __paginginit pgdat_init_internals(struct pglist_data *pgdat)
 {
-	enum zone_type j;
-	int nid = pgdat->node_id;
-
 	pgdat_resize_init(pgdat);
-
 	pgdat_init_numabalancing(pgdat);
 	pgdat_init_split_queue(pgdat);
 	pgdat_init_kcompactd(pgdat);
@@ -6262,7 +6250,56 @@ static void __paginginit free_area_init_core(struct pglist_data *pgdat)
 	pgdat_page_ext_init(pgdat);
 	spin_lock_init(&pgdat->lru_lock);
 	lruvec_init(node_lruvec(pgdat));
+}
+
+static void __paginginit zone_init_internals(struct zone *zone, enum zone_type idx, int nid,
+							unsigned long remaining_pages)
+{
+	zone->managed_pages = remaining_pages;
+	zone_set_nid(zone, nid);
+	zone->name = zone_names[idx];
+	zone->zone_pgdat = NODE_DATA(nid);
+	spin_lock_init(&zone->lock);
+	zone_seqlock_init(zone);
+	zone_pcp_init(zone);
+}
+
+/*
+ * Set up the zone data structures
+ * - init pgdat internals
+ * - init all zones belonging to this node
+ *
+ * NOTE: this function is only called during memory hotplug
+ */
+#ifdef CONFIG_MEMORY_HOTPLUG
+void __paginginit free_area_init_core_hotplug(int nid)
+{
+	enum zone_type j;
+	pg_data_t *pgdat = NODE_DATA(nid);
+
+	pgdat_init_internals(pgdat);
+	for (j = 0; j < MAX_NR_ZONES; j++) {
+		struct zone *zone = pgdat->node_zones + j;
+		zone_init_internals(zone, j, nid, 0);
+	}
+}
+#endif
+
+/*
+ * Set up the zone data structures:
+ *   - mark all pages reserved
+ *   - mark all memory queues empty
+ *   - clear the memory bitmaps
+ *
+ * NOTE: pgdat should get zeroed by caller.
+ * NOTE: this function is only called during early init.
+ */
+static void __init free_area_init_core(struct pglist_data *pgdat)
+{
+	enum zone_type j;
+	int nid = pgdat->node_id;
 
+	pgdat_init_internals(pgdat);
 	pgdat->per_cpu_nodestats = &boot_nodestats;
 
 	for (j = 0; j < MAX_NR_ZONES; j++) {
@@ -6310,13 +6347,7 @@ static void __paginginit free_area_init_core(struct pglist_data *pgdat)
 		 * when the bootmem allocator frees pages into the buddy system.
 		 * And all highmem pages will be managed by the buddy system.
 		 */
-		zone->managed_pages = freesize;
-		zone_set_nid(zone, nid);
-		zone->name = zone_names[j];
-		zone->zone_pgdat = pgdat;
-		spin_lock_init(&zone->lock);
-		zone_seqlock_init(zone);
-		zone_pcp_init(zone);
+		zone_init_internals(zone, j, nid, freesize);
 
 		if (!size)
 			continue;
-- 
2.13.6