[RFC PATCH v3 24/35] mm: Propagate the sorted-buddy bias for picking free regions, to region allocator

["Srivatsa S. Bhat" <srivatsa.bhat@xxxxxxxxxxxxxxxxxx>]

The sorted-buddy page allocator keeps the buddy freelists sorted region-wise,
and tries to pick lower numbered regions while allocating pages. The idea is
to allocate regions in the increasing order of region number.

Propagate the same bias to the region allocator as well. That is, make it
favor lower numbered regions while allocating regions to the page allocator.
To do this efficiently, add a bitmap to represent the regions in the region
allocator, and use bitmap operations to manage these regions and to pick the
lowest numbered free region efficiently.

Signed-off-by: Srivatsa S. Bhat <srivatsa.bhat@xxxxxxxxxxxxxxxxxx>
---

 include/linux/mmzone.h |    1 +
 mm/page_alloc.c        |   19 ++++++++++++++++++-
 2 files changed, 19 insertions(+), 1 deletion(-)

diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index c2956dd..8c6e9f1 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -125,6 +125,7 @@ struct mem_region {
 struct region_allocator {
 	struct mem_region	region[MAX_NR_ZONE_REGIONS];
 	int			next_region;
+	DECLARE_BITMAP(ralloc_mask, MAX_NR_ZONE_REGIONS);
 };
 
 struct pglist_data;
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 78ae8f6..7e82872a 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -934,7 +934,7 @@ static void add_to_region_allocator(struct zone *z, struct free_list *free_list,
 	struct free_area_region *reg_area;
 	struct list_head *ralloc_list;
 	unsigned long nr_pages;
-	int order;
+	int order, *next_region;
 
 	if (WARN_ON(list_empty(&free_list->list)))
 		return;
@@ -951,6 +951,13 @@ static void add_to_region_allocator(struct zone *z, struct free_list *free_list,
 
 	WARN_ON(reg_area->nr_free != 0);
 	reg_area->nr_free += nr_pages;
+
+	set_bit(region_id, reg_alloc->ralloc_mask);
+	next_region = &reg_alloc->next_region;
+
+	if ((*next_region < 0) ||
+			(*next_region > 0 && region_id < *next_region))
+		*next_region = region_id;
 }
 
 /* Delete freepages from the region allocator and add them to buddy freelists */
@@ -981,6 +988,16 @@ static int del_from_region_allocator(struct zone *zone, unsigned int order,
 	reg_area->nr_free -= nr_pages;
 	WARN_ON(reg_area->nr_free != 0);
 
+	/* Pick a new next_region */
+	clear_bit(next_region, reg_alloc->ralloc_mask);
+	next_region = find_first_bit(reg_alloc->ralloc_mask,
+				     MAX_NR_ZONE_REGIONS);
+
+	if (next_region >= MAX_NR_ZONE_REGIONS)
+		next_region = -1; /* No free regions available */
+
+	reg_alloc->next_region = next_region;
+
 	return 0;
 }
 

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