[PATCH 6/9] fragmentation avoidance core

From: Joel Schopp
Date: Mon Sep 26 2005 - 15:14:01 EST

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This patch is the core changes for memory fragmentation avoidance.

__rmqueue() within an alloctype behaves much as it did before on the global
list. If that alloctype has insufficient free blocks it trys to
steal a unallocated 2^MAX_ORDER-1 block from another type. If there are no
unallocated 2^MAX_ORDER-1 blocks it goes to a more aggressive fallback
allocation detailed in a later patch.

The other functions do basically the same thing they did before, they just get
tidied up to deal with 3 alloctypes.

As this patch replaces all references to free_area[] with free_area_lists[] it
removes free_area[]

Signed-off-by: Mel Gorman <mel@xxxxxxxxx>
Signed-off-by: Joel Schopp <jschopp@xxxxxxxxxxxxxx>
Index: 2.6.13-joel2/mm/page_alloc.c
===================================================================
--- 2.6.13-joel2.orig/mm/page_alloc.c 2005-09-20 15:08:05.%N -0500
+++ 2.6.13-joel2/mm/page_alloc.c 2005-09-21 11:13:14.%N -0500
@@ -104,7 +104,9 @@ void assign_bit(int bit_nr, unsigned lon
* Reserve a block of pages for an allocation type & enforce function
* being changed if more bits are added to keep track of additional types
*/
-BUILD_BUG_ON(BITS_PER_RCLM_TYPE > 2)
+#if BITS_PER_RCLM_TYPE > 2
+#error
+#endif
static inline void set_pageblock_type(struct zone *zone, struct page *page,
int type)
{
@@ -333,6 +335,8 @@ static inline void __free_pages_bulk (st
{
unsigned long page_idx;
int order_size = 1 << order;
+ struct free_area *area;
+ struct free_area *freelist;

if (unlikely(order))
destroy_compound_page(page, order);
@@ -342,10 +346,11 @@ static inline void __free_pages_bulk (st
BUG_ON(page_idx & (order_size - 1));
BUG_ON(bad_range(zone, page));

+ freelist = zone->free_area_lists[get_pageblock_type(zone,page)];
+
zone->free_pages += order_size;
while (order < MAX_ORDER-1) {
unsigned long combined_idx;
- struct free_area *area;
struct page *buddy;

combined_idx = __find_combined_index(page_idx, order);
@@ -356,16 +361,20 @@ static inline void __free_pages_bulk (st
if (!page_is_buddy(buddy, order))
break; /* Move the buddy up one level. */
list_del(&buddy->lru);
- area = zone->free_area + order;
+ area = freelist + order;
area->nr_free--;
rmv_page_order(buddy);
page = page + (combined_idx - page_idx);
page_idx = combined_idx;
order++;
}
+ if (unlikely(order == MAX_ORDER-1)) zone->fallback_balance++;
+
set_page_order(page, order);
- list_add(&page->lru, &zone->free_area[order].free_list);
- zone->free_area[order].nr_free++;
+ area = freelist + order;
+ list_add_tail(&page->lru, &area->free_list);
+ area->nr_free++;
+
}

static inline void free_pages_check(const char *function, struct page *page)
@@ -555,6 +564,25 @@ static inline struct page* steal_largepa
return page;
}

+static inline struct page
+*remove_page(struct zone *zone, struct page *page, unsigned int order,
+ unsigned int current_order, struct free_area *area)
+{
+ if (unlikely(current_order == MAX_ORDER-1)) zone->fallback_balance--;
+ list_del(&page->lru);
+ rmv_page_order(page);
+ zone->free_pages -= 1UL << order;
+ return expand(zone, page, order, current_order, area);
+}
+
+
+static struct page *
+fallback_alloc(int alloctype, struct zone *zone, unsigned int order)
+{
+ /* Stub out for seperate review, NULL equates to no fallback*/
+ return NULL;
+
+}
/*
* Do the hard work of removing an element from the buddy allocator.
* Call me with the zone->lock already held.
@@ -566,20 +594,24 @@ static struct page *__rmqueue(struct zon
unsigned int current_order;
struct page *page;

- for (current_order = order; current_order < MAX_ORDER; ++current_order) {
- area = zone->free_area + current_order;
- if (list_empty(&area->free_list))
- continue;
-
+ alloctype >>= RCLM_SHIFT;
+ /* Search the list for the alloctype */
+ area = zone->free_area_lists[alloctype] + order;
+ for (current_order = order; current_order < MAX_ORDER;
+ current_order++, area++) {
+ if (list_empty(&area->free_list)) continue;
page = list_entry(area->free_list.next, struct page, lru);
- list_del(&page->lru);
- rmv_page_order(page);
- area->nr_free--;
- zone->free_pages -= 1UL << order;
- return expand(zone, page, order, current_order, area);
+ area->nr_free--;
+ return remove_page(zone, page, order, current_order, area);
}

- return NULL;
+ page = steal_largepage(zone, alloctype);
+ if (page == NULL)
+ return fallback_alloc(alloctype, zone, order);
+
+ area--;
+ current_order--;
+ return remove_page(zone, page, order, current_order, area);
}

/*
@@ -587,25 +619,49 @@ static struct page *__rmqueue(struct zon
* a single hold of the lock, for efficiency. Add them to the supplied list.
* Returns the number of new pages which were placed at *list.
*/
-static int rmqueue_bulk(struct zone *zone, unsigned int order,
- unsigned long count, struct list_head *list,
- int alloctype)
+static int rmqueue_bulk(struct zone *zone, unsigned long count,
+ struct list_head *list, int alloctype)
{
unsigned long flags;
int i;
- int allocated = 0;
+ unsigned long allocated = count;
struct page *page;
-
+ unsigned long current_order = 0;
+ /* Find what order we should start allocating blocks at */
+ current_order = ffs(count) - 1;
+
+
+ /*
+ * Satisfy the request in as the largest possible physically
+ * contiguous block
+ */
spin_lock_irqsave(&zone->lock, flags);
- for (i = 0; i < count; ++i) {
- page = __rmqueue(zone, order, alloctype);
- if (page == NULL)
- break;
- allocated++;
- list_add_tail(&page->lru, list);
+ while (allocated) {
+ if ((1 << current_order) > allocated)
+ current_order--;
+
+ /* Allocate a block at the current_order */
+ page = __rmqueue(zone, current_order, alloctype);
+ if (page == NULL) {
+ if (current_order == 0) break;
+ current_order--;
+ continue;
+ }
+ allocated -= 1 << current_order;
+ /* Move to the next block if order is already 0 */
+ if (current_order == 0) {
+ list_add_tail(&page->lru, list);
+ continue;
+ }
+
+ /* Split the large block into order-sized blocks */
+ for (i = 1 << current_order; i != 0; i--) {
+ list_add_tail(&page->lru, list);
+ page++;
+ }
}
spin_unlock_irqrestore(&zone->lock, flags);
- return allocated;
+ return count - allocated;
}

#ifdef CONFIG_NUMA
@@ -664,9 +720,9 @@ static void __drain_pages(unsigned int c
void mark_free_pages(struct zone *zone)
{
unsigned long zone_pfn, flags;
- int order;
+ int order, type;
+ unsigned long start_pfn, i;
struct list_head *curr;
-
if (!zone->spanned_pages)
return;

@@ -674,14 +730,15 @@ void mark_free_pages(struct zone *zone)
for (zone_pfn = 0; zone_pfn < zone->spanned_pages; ++zone_pfn)
ClearPageNosaveFree(pfn_to_page(zone_pfn + zone->zone_start_pfn));

- for (order = MAX_ORDER - 1; order >= 0; --order)
- list_for_each(curr, &zone->free_area[order].free_list) {
- unsigned long start_pfn, i;
-
- start_pfn = page_to_pfn(list_entry(curr, struct page, lru));
-
+ for (type=0; type < RCLM_TYPES; type++) {
+ for (order = MAX_ORDER - 1; order >= 0; --order)
+ list_for_each(curr, &zone->free_area_lists[type]
+ [order].free_list) {
+ start_pfn = page_to_pfn(list_entry(curr, struct page,
+ lru));
for (i=0; i < (1<<order); i++)
SetPageNosaveFree(pfn_to_page(start_pfn+i));
+ }
}
spin_unlock_irqrestore(&zone->lock, flags);
}
@@ -790,7 +847,7 @@ buffered_rmqueue(struct zone *zone, int
pcp = &zone_pcp(zone, get_cpu())->pcp[cold];
local_irq_save(flags);
if (pcp->count <= pcp->low)
- pcp->count += rmqueue_bulk(zone, 0, pcp->batch,
+ pcp->count += rmqueue_bulk(zone, pcp->batch,
&pcp->list, alloctype);
if (pcp->count) {
page = list_entry(pcp->list.next, struct page, lru);
@@ -831,6 +888,7 @@ int zone_watermark_ok(struct zone *z, in
/* free_pages my go negative - that's OK */
long min = mark, free_pages = z->free_pages - (1 << order) + 1;
int o;
+ struct free_area *kernnorclm, *kernrclm, *userrclm;

if (gfp_high)
min -= min / 2;
@@ -839,15 +897,21 @@ int zone_watermark_ok(struct zone *z, in

if (free_pages <= min + z->lowmem_reserve[classzone_idx])
return 0;
+ kernnorclm = z->free_area_lists[RCLM_NORCLM];
+ kernrclm = z->free_area_lists[RCLM_KERN];
+ userrclm = z->free_area_lists[RCLM_USER];
for (o = 0; o < order; o++) {
/* At the next order, this order's pages become unavailable */
- free_pages -= z->free_area[o].nr_free << o;
-
+ free_pages -= (kernnorclm->nr_free + kernrclm->nr_free +
+ userrclm->nr_free) << o;
/* Require fewer higher order pages to be free */
min >>= 1;

if (free_pages <= min)
return 0;
+ kernnorclm++;
+ kernrclm++;
+ userrclm++;
}
return 1;
}
@@ -1370,6 +1434,7 @@ void show_free_areas(void)
unsigned long inactive;
unsigned long free;
struct zone *zone;
+ int type;

for_each_zone(zone) {
show_node(zone);
@@ -1463,8 +1528,10 @@ void show_free_areas(void)

spin_lock_irqsave(&zone->lock, flags);
for (order = 0; order < MAX_ORDER; order++) {
- nr = zone->free_area[order].nr_free;
- total += nr << order;
+ for (type=0; type < RCLM_TYPES; type++) {
+ nr = zone->free_area_lists[type][order].nr_free;
+ total += nr << order;
+ }
printk("%lu*%lukB ", nr, K(1UL) << order);
}
spin_unlock_irqrestore(&zone->lock, flags);
@@ -2171,16 +2238,36 @@ static int frag_show(struct seq_file *m,
struct zone *zone;
struct zone *node_zones = pgdat->node_zones;
unsigned long flags;
- int order;
+ int order, type;
+ struct list_head *elem;
+ unsigned long nr_bufs = 0;

for (zone = node_zones; zone - node_zones < MAX_NR_ZONES; ++zone) {
if (!zone->present_pages)
continue;

spin_lock_irqsave(&zone->lock, flags);
- seq_printf(m, "Node %d, zone %8s ", pgdat->node_id, zone->name);
- for (order = 0; order < MAX_ORDER; ++order)
- seq_printf(m, "%6lu ", zone->free_area[order].nr_free);
+ seq_printf(m, "Node %d, zone %8s", pgdat->node_id, zone->name);
+ for (order = 0; order < MAX_ORDER-1; ++order) {
+ nr_bufs = 0;
+
+ for (type=0; type < RCLM_TYPES; type++) {
+ list_for_each(elem,
+ &(zone->free_area_lists[type]
+ [order].free_list))
+ ++nr_bufs;
+ }
+ seq_printf(m, "%6lu ", nr_bufs);
+ }
+
+ /* Scan global list */
+ nr_bufs = 0;
+ for (type=0; type < RCLM_TYPES; type++) {
+ nr_bufs += zone->free_area_lists[type]
+ [MAX_ORDER-1].nr_free;
+ }
+ seq_printf(m, "%6lu ", nr_bufs);
+
spin_unlock_irqrestore(&zone->lock, flags);
seq_putc(m, '\n');
}
Index: 2.6.13-joel2/include/linux/mmzone.h
===================================================================
--- 2.6.13-joel2.orig/include/linux/mmzone.h 2005-09-20 15:04:47.%N -0500
+++ 2.6.13-joel2/include/linux/mmzone.h 2005-09-21 10:44:00.%N -0500
@@ -152,11 +152,7 @@ struct zone {
* free areas of different sizes
*/
spinlock_t lock;
- /*
- * free_area to be removed in later patch as it is replaced by
- * free_area_list
- */
- struct free_area free_area[MAX_ORDER];
+
#ifndef CONFIG_SPARSEMEM
/*
* The map tracks what each 2^MAX_ORDER-1 sized block is being used for.

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