[RFC PATCH v3 23/35] mm: Maintain the counter for freepages in the region allocator

[Srivatsa S. Bhat]

We have a field named 'nr_free' for every memory-region in the region
allocator. Keep it updated with the count of freepages in that region.

We already run a loop while moving freepages in bulk between the buddy
allocator and the region allocator. Reuse that to update the freepages
count as well.

Signed-off-by: Srivatsa S. Bhat <srivatsa.b...@linux.vnet.ibm.com>
---

 mm/page_alloc.c |   45 ++++++++++++++++++++++++++++++++++-----------
 1 file changed, 34 insertions(+), 11 deletions(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 5b58e7d..78ae8f6 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -696,10 +696,12 @@ out:
  * Add all the freepages contained in 'list' to the buddy freelist
  * 'free_list'. Using suitable list-manipulation tricks, we move the
  * pages between the lists in one shot.
+ *
+ * Returns the number of pages moved.
  */
-static void add_to_freelist_bulk(struct list_head *list,
-                                struct free_list *free_list, int order,
-                                int region_id)
+static unsigned long
+add_to_freelist_bulk(struct list_head *list, struct free_list *free_list,
+                    int order, int region_id)
 {
        struct list_head *cur, *position;
        struct mem_region_list *region;
@@ -708,7 +710,7 @@ static void add_to_freelist_bulk(struct list_head *list,
        struct page *page;
 
        if (list_empty(list))
-               return;
+               return 0;
 
        page = list_first_entry(list, struct page, lru);
        list_del(&page->lru);
@@ -736,6 +738,8 @@ static void add_to_freelist_bulk(struct list_head *list,
 
        /* Fix up the zone region stats, since add_to_freelist() altered it */
        region->zone_region->nr_free -= 1 << order;
+
+       return nr_pages + 1;
 }
 
 /**
@@ -857,10 +861,12 @@ page_found:
  * Delete all freepages belonging to the region 'region_id' from 'free_list'
  * and move them to 'list'. Using suitable list-manipulation tricks, we move
  * the pages between the lists in one shot.
+ *
+ * Returns the number of pages moved.
  */
-static void del_from_freelist_bulk(struct list_head *list,
-                                  struct free_list *free_list, int order,
-                                  int region_id)
+static unsigned long
+del_from_freelist_bulk(struct list_head *list, struct free_list *free_list,
+                      int order, int region_id)
 {
        struct mem_region_list *region, *prev_region;
        unsigned long nr_pages = 0;
@@ -906,6 +912,8 @@ static void del_from_freelist_bulk(struct list_head *list,
 
        /* Fix up the zone region stats, since del_from_freelist() altered it */
        region->zone_region->nr_free += 1 << order;
+
+       return nr_pages + 1;
 }
 
 /**
@@ -923,7 +931,9 @@ static void add_to_region_allocator(struct zone *z, struct 
free_list *free_list,
                                    int region_id)
 {
        struct region_allocator *reg_alloc;
+       struct free_area_region *reg_area;
        struct list_head *ralloc_list;
+       unsigned long nr_pages;
        int order;
 
        if (WARN_ON(list_empty(&free_list->list)))
@@ -933,9 +943,14 @@ static void add_to_region_allocator(struct zone *z, struct 
free_list *free_list,
                                            struct page, lru));
 
        reg_alloc = &z->region_allocator;
-       ralloc_list = &reg_alloc->region[region_id].region_area[order].list;
+       reg_area = &reg_alloc->region[region_id].region_area[order];
+       ralloc_list = &reg_area->list;
+
+       nr_pages = del_from_freelist_bulk(ralloc_list, free_list, order,
+                                         region_id);
 
-       del_from_freelist_bulk(ralloc_list, free_list, order, region_id);
+       WARN_ON(reg_area->nr_free != 0);
+       reg_area->nr_free += nr_pages;
 }
 
 /* Delete freepages from the region allocator and add them to buddy freelists 
*/
@@ -943,8 +958,10 @@ static int del_from_region_allocator(struct zone *zone, 
unsigned int order,
                                     int migratetype)
 {
        struct region_allocator *reg_alloc;
+       struct free_area_region *reg_area;
        struct list_head *ralloc_list;
        struct free_list *free_list;
+       unsigned long nr_pages;
        int next_region;
 
        reg_alloc = &zone->region_allocator;
@@ -953,10 +970,16 @@ static int del_from_region_allocator(struct zone *zone, 
unsigned int order,
        if (next_region < 0)
                return -ENOMEM;
 
-       ralloc_list = &reg_alloc->region[next_region].region_area[order].list;
+       reg_area = &reg_alloc->region[next_region].region_area[order];
+       ralloc_list = &reg_area->list;
+
        free_list = &zone->free_area[order].free_list[migratetype];
 
-       add_to_freelist_bulk(ralloc_list, free_list, order, next_region);
+       nr_pages = add_to_freelist_bulk(ralloc_list, free_list, order,
+                                       next_region);
+
+       reg_area->nr_free -= nr_pages;
+       WARN_ON(reg_area->nr_free != 0);
 
        return 0;
 }

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