[PATCH] make try_to_free_pages walk zonelist

From: Rik van Riel <riel@surriel.com>

In 2.6.0 both __alloc_pages() and the corresponding wakeup_kswapd()s walk
all zones in the zone list, possibly spanning multiple nodes in a low numa
factor system like AMD64.

Also, if lower_zone_protection is set in /proc, then it may be possible
that kswapd never cleans out data in zones further down the zonelist and
try_to_free_pages needs to do that.

However, in 2.6.0 try_to_free_pages() only frees pages in the pgdat the
first zone in the zonelist belongs to.

This is probably the wrong behaviour, since both the page allocator and the
kswapd wakeup free things from all zones on the zonelist.  The following
patch makes try_to_free_pages() consistent with the allocator, by passing
the zonelist as an argument and freeing pages from all zones in the list.

I do not have any numa systems myself, so I have only tested it on my own
little smp box.  Testing on NUMA systems may be useful, though the patch
really only should have an impact in those rare cases where kswapd can't
keep up with allocations...

As a side effect, the patch shrinks the kernel by 2 lines and replaces some
subtle magic by a simpler array walk.

fs/buffer.c

@@ -483,7 +483,7 @@ void invalidate_bdev(struct block_device *bdev, int destroy_dirty_buffers)
  */
 static void free_more_memory(void)
 {
-	struct zone *zone;
+	struct zone **zones;
 	pg_data_t *pgdat;
 
 	wakeup_bdflush(1024);
@@ -491,9 +491,9 @@ static void free_more_memory(void)
 	yield();
 
 	for_each_pgdat(pgdat) {
-		zone = pgdat->node_zonelists[GFP_NOFS&GFP_ZONEMASK].zones[0];
-		if (zone)
-			try_to_free_pages(zone, GFP_NOFS, 0);
+		zones = pgdat->node_zonelists[GFP_NOFS&GFP_ZONEMASK].zones;
+		if (*zones)
+			try_to_free_pages(zones, GFP_NOFS, 0);
 	}
 }
 

include/linux/swap.h

@@ -173,7 +173,7 @@ extern int rotate_reclaimable_page(struct page *page);
 extern void swap_setup(void);
 
 /* linux/mm/vmscan.c */
-extern int try_to_free_pages(struct zone *, unsigned int, unsigned int);
+extern int try_to_free_pages(struct zone **, unsigned int, unsigned int);
 extern int shrink_all_memory(int);
 extern int vm_swappiness;
 

mm/page_alloc.c

@@ -539,7 +539,7 @@ __alloc_pages(unsigned int gfp_mask, unsigned int order,
 {
 	const int wait = gfp_mask & __GFP_WAIT;
 	unsigned long min;
-	struct zone **zones, *classzone;
+	struct zone **zones;
 	struct page *page;
 	struct reclaim_state reclaim_state;
 	struct task_struct *p = current;
@@ -554,8 +554,7 @@ __alloc_pages(unsigned int gfp_mask, unsigned int order,
 		cold = 1;
 
 	zones = zonelist->zones;  /* the list of zones suitable for gfp_mask */
-	classzone = zones[0]; 
-	if (classzone == NULL)    /* no zones in the zonelist */
+	if (zones[0] == NULL)     /* no zones in the zonelist */
 		return NULL;
 
 	/* Go through the zonelist once, looking for a zone with enough free */
@@ -630,7 +629,7 @@ __alloc_pages(unsigned int gfp_mask, unsigned int order,
 	reclaim_state.reclaimed_slab = 0;
 	p->reclaim_state = &reclaim_state;
 
-	try_to_free_pages(classzone, gfp_mask, order);
+	try_to_free_pages(zones, gfp_mask, order);
 
 	p->reclaim_state = NULL;
 	p->flags &= ~PF_MEMALLOC;

mm/vmscan.c

@@ -803,16 +803,15 @@ shrink_zone(struct zone *zone, int max_scan, unsigned int gfp_mask,
  * scan then give up on it.
  */
 static int
-shrink_caches(struct zone *classzone, int priority, int *total_scanned,
+shrink_caches(struct zone **zones, int priority, int *total_scanned,
 		int gfp_mask, int nr_pages, struct page_state *ps)
 {
-	struct zone *first_classzone;
-	struct zone *zone;
 	int ret = 0;
+	int i;
 
-	first_classzone = classzone->zone_pgdat->node_zones;
-	for (zone = classzone; zone >= first_classzone; zone--) {
+	for (i = 0; zones[i] != NULL; i++) {
 		int to_reclaim = max(nr_pages, SWAP_CLUSTER_MAX);
+		struct zone *zone = zones[i];
 		int nr_mapped = 0;
 		int max_scan;
 
@@ -855,27 +854,27 @@ shrink_caches(struct zone *classzone, int priority, int *total_scanned,
  * excessive rotation of the inactive list, which is _supposed_ to be an LRU,
  * yes?
  */
-int try_to_free_pages(struct zone *cz,
+int try_to_free_pages(struct zone **zones,
 		unsigned int gfp_mask, unsigned int order)
 {
 	int priority;
 	int ret = 0;
 	const int nr_pages = SWAP_CLUSTER_MAX;
 	int nr_reclaimed = 0;
-	struct zone *zone;
 	struct reclaim_state *reclaim_state = current->reclaim_state;
+	int i;
 
 	inc_page_state(allocstall);
 
-	for (zone = cz; zone >= cz->zone_pgdat->node_zones; --zone)
-		zone->temp_priority = DEF_PRIORITY;
+	for (i = 0; zones[i] != 0; i++)
+		zones[i]->temp_priority = DEF_PRIORITY;
 
 	for (priority = DEF_PRIORITY; priority >= 0; priority--) {
 		int total_scanned = 0;
 		struct page_state ps;
 
 		get_page_state(&ps);
-		nr_reclaimed += shrink_caches(cz, priority, &total_scanned,
+		nr_reclaimed += shrink_caches(zones, priority, &total_scanned,
 						gfp_mask, nr_pages, &ps);
 		if (nr_reclaimed >= nr_pages) {
 			ret = 1;
@@ -892,7 +891,7 @@ int try_to_free_pages(struct zone *cz,
 
 		/* Take a nap, wait for some writeback to complete */
 		blk_congestion_wait(WRITE, HZ/10);
-		if (cz - cz->zone_pgdat->node_zones < ZONE_HIGHMEM) {
+		if (zones[0] - zones[0]->zone_pgdat->node_zones < ZONE_HIGHMEM) {
 			shrink_slab(total_scanned, gfp_mask);
 			if (reclaim_state) {
 				nr_reclaimed += reclaim_state->reclaimed_slab;
@@ -903,8 +902,8 @@ int try_to_free_pages(struct zone *cz,
 	if ((gfp_mask & __GFP_FS) && !(gfp_mask & __GFP_NORETRY))
 		out_of_memory();
 out:
-	for (zone = cz; zone >= cz->zone_pgdat->node_zones; --zone)
-		zone->prev_priority = zone->temp_priority;
+	for (i = 0; zones[i] != 0; i++)
+		zones[i]->prev_priority = zones[i]->temp_priority;
 	return ret;
 }