[PATCH RFC] higher order allocs 2.4.10-pre9-recycle-R1

[Roger Larsson <roger.larsson@norran.net>]

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Hi again,

Summary: Keep more pages free if lots of higher order pages has been used. 

* Suppose returned higher order pages is not returned to the free list
  but to another per zone and order list.
  Then they will not be missing when needed again later.

But there are drawbacks... pages will not be merged. Cant be used for lower
order allocs if never needed again...

So, what will happen if they are placed on the ordinary free list - but
not counted as free?

* We will free more pages and that will make it more unlikely that they
  will be needed. But they are still there for fast allocs. And they can
  merge into higher order pages.

I have made some test runs - results are close to proper 2.4.10-pre9
actually slightly better for all but two of mine testcases.
diff of two files bigger than RAM got half throughput, why???
mmap002 (use all memory attempt) took more than three times as long -
less memory to use at once, OK. And not necessarily a bad thing.

(I will be away from my computer for some days - back on Tuesday)

/RogerL

-- 
Roger Larsson
Skelleftea
Sweden

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*******************************************
Patch prepared by: roger.larsson@norran.net
Name of file: /home/roger/patches/patch-2.4.10-pre9-recycle-R1

--- linux/mm/page_alloc.c.orig	Sat Sep 15 17:30:32 2001
+++ linux/mm/page_alloc.c	Sun Sep 16 00:01:24 2001
@@ -104,7 +104,12 @@
 
 	spin_lock_irqsave(&zone->lock, flags);
 
-	zone->free_pages -= mask;
+	area->recycled++;
+	if (area->recycled <= 0)
+		area->recycled=1;
+
+	if (!order || area->recycled < 0)
+		zone->free_pages -= mask;
 
 	while (mask + (1 << (MAX_ORDER-1))) {
 		struct page *buddy1, *buddy2;
@@ -193,9 +198,14 @@
 			index = page - zone->zone_mem_map;
 			if (curr_order != MAX_ORDER-1)
 				MARK_USED(index, curr_order, area);
-			zone->free_pages -= 1 << order;
 
 			page = expand(zone, page, index, order, curr_order, area);
+			/* use initial area, requested order */
+			area=zone->free_area + order;
+			area->recycled--; /* might go neg, fixed in free */
+			if (!order || area->recycled < 0)
+				zone->free_pages -= 1 << order;
+
 			spin_unlock_irqrestore(&zone->lock, flags);
 
 			set_page_count(page, 1);
@@ -653,7 +663,8 @@
 		if (zone->size) {
 			spin_lock_irqsave(&zone->lock, flags);
 		 	for (order = 0; order < MAX_ORDER; order++) {
-				head = &(zone->free_area + order)->free_list;
+				free_area_t *area = zone->free_area + order;
+				head = &area->free_list;
 				curr = head;
 				nr = 0;
 				for (;;) {
@@ -663,8 +674,9 @@
 					nr++;
 				}
 				total += nr * (1 << order);
-				printk("%lu*%lukB ", nr,
-						(PAGE_SIZE>>10) << order);
+				printk("%lu/%ld*%lukB ", nr,
+				       area->recycled,
+				       (PAGE_SIZE>>10) << order);
 			}
 			spin_unlock_irqrestore(&zone->lock, flags);
 		}
@@ -891,6 +903,7 @@
 			bitmap_size = LONG_ALIGN(bitmap_size+1);
 			zone->free_area[i].map = 
 			  (unsigned long *) alloc_bootmem_node(pgdat, bitmap_size);
+			zone->free_area[i].recycled = 0;
 		}
 	}
 	build_zonelists(pgdat);
--- linux/include/linux/mmzone.h.orig	Sat Sep 15 21:58:47 2001
+++ linux/include/linux/mmzone.h	Sat Sep 15 22:01:29 2001
@@ -21,6 +21,7 @@
 typedef struct free_area_struct {
 	struct list_head	free_list;
 	unsigned long		*map;
+	long                    recycled;
 } free_area_t;
 
 struct pglist_data;