[PATCH 05/11] Export unusable free space index via /proc/unusable_index

[Mel Gorman <mel@csn.ul.ie>]

Unusable free space index is a measure of external fragmentation that
takes the allocation size into account. For the most part, the huge page
size will be the size of interest but not necessarily so it is exported
on a per-order and per-zone basis via /proc/unusable_index.

The index is a value between 0 and 1. It can be expressed as a
percentage by multiplying by 100 as documented in
Documentation/filesystems/proc.txt.

Signed-off-by: Mel Gorman <mel@csn.ul.ie>
Reviewed-by: Minchan Kim <minchan.kim@gmail.com>
Acked-by: Rik van Riel <riel@redhat.com>
---
 Documentation/filesystems/proc.txt |   13 ++++-
 mm/vmstat.c                        |  120 ++++++++++++++++++++++++++++++++++++
 2 files changed, 132 insertions(+), 1 deletions(-)

diff --git a/Documentation/filesystems/proc.txt b/Documentation/filesystems/proc.txt
index 5e132b5..5c4b0fb 100644
--- a/Documentation/filesystems/proc.txt
+++ b/Documentation/filesystems/proc.txt
@@ -452,6 +452,7 @@ Table 1-5: Kernel info in /proc
  sys         See chapter 2                                     
  sysvipc     Info of SysVIPC Resources (msg, sem, shm)		(2.4)
  tty	     Info of tty drivers
+ unusable_index Additional page allocator information (see text)(2.5)
  uptime      System uptime                                     
  version     Kernel version                                    
  video	     bttv info of video resources			(2.4)
@@ -609,7 +610,7 @@ ZONE_DMA, 4 chunks of 2^1*PAGE_SIZE in ZONE_DMA, 101 chunks of 2^4*PAGE_SIZE
 available in ZONE_NORMAL, etc... 
 
 More information relevant to external fragmentation can be found in
-pagetypeinfo.
+pagetypeinfo and unusable_index
 
 > cat /proc/pagetypeinfo
 Page block order: 9
@@ -650,6 +651,16 @@ unless memory has been mlock()'d. Some of the Reclaimable blocks should
 also be allocatable although a lot of filesystem metadata may have to be
 reclaimed to achieve this.
 
+> cat /proc/unusable_index
+Node 0, zone      DMA 0.000 0.000 0.000 0.001 0.005 0.013 0.021 0.037 0.037 0.101 0.230
+Node 0, zone   Normal 0.000 0.000 0.000 0.001 0.002 0.002 0.005 0.015 0.028 0.028 0.054
+
+The unusable free space index measures how much of the available free
+memory cannot be used to satisfy an allocation of a given size and is a
+value between 0 and 1. The higher the value, the more of free memory is
+unusable and by implication, the worse the external fragmentation is. This
+can be expressed as a percentage by multiplying by 100.
+
 ..............................................................................
 
 meminfo:
diff --git a/mm/vmstat.c b/mm/vmstat.c
index 7f760cb..ca42e10 100644
--- a/mm/vmstat.c
+++ b/mm/vmstat.c
@@ -453,6 +453,106 @@ static int frag_show(struct seq_file *m, void *arg)
 	return 0;
 }
 
+
+struct contig_page_info {
+	unsigned long free_pages;
+	unsigned long free_blocks_total;
+	unsigned long free_blocks_suitable;
+};
+
+/*
+ * Calculate the number of free pages in a zone, how many contiguous
+ * pages are free and how many are large enough to satisfy an allocation of
+ * the target size. Note that this function makes to attempt to estimate
+ * how many suitable free blocks there *might* be if MOVABLE pages were
+ * migrated. Calculating that is possible, but expensive and can be
+ * figured out from userspace
+ */
+static void fill_contig_page_info(struct zone *zone,
+				unsigned int suitable_order,
+				struct contig_page_info *info)
+{
+	unsigned int order;
+
+	info->free_pages = 0;
+	info->free_blocks_total = 0;
+	info->free_blocks_suitable = 0;
+
+	for (order = 0; order < MAX_ORDER; order++) {
+		unsigned long blocks;
+
+		/* Count number of free blocks */
+		blocks = zone->free_area[order].nr_free;
+		info->free_blocks_total += blocks;
+
+		/* Count free base pages */
+		info->free_pages += blocks << order;
+
+		/* Count the suitable free blocks */
+		if (order >= suitable_order)
+			info->free_blocks_suitable += blocks <<
+						(order - suitable_order);
+	}
+}
+
+/*
+ * Return an index indicating how much of the available free memory is
+ * unusable for an allocation of the requested size.
+ */
+static int unusable_free_index(unsigned int order,
+				struct contig_page_info *info)
+{
+	/* No free memory is interpreted as all free memory is unusable */
+	if (info->free_pages == 0)
+		return 1000;
+
+	/*
+	 * Index should be a value between 0 and 1. Return a value to 3
+	 * decimal places.
+	 *
+	 * 0 => no fragmentation
+	 * 1 => high fragmentation
+	 */
+	return ((info->free_pages - (info->free_blocks_suitable << order)) * 1000) / info->free_pages;
+
+}
+
+static void unusable_show_print(struct seq_file *m,
+					pg_data_t *pgdat, struct zone *zone)
+{
+	unsigned int order;
+	int index;
+	struct contig_page_info info;
+
+	seq_printf(m, "Node %d, zone %8s ",
+				pgdat->node_id,
+				zone->name);
+	for (order = 0; order < MAX_ORDER; ++order) {
+		fill_contig_page_info(zone, order, &info);
+		index = unusable_free_index(order, &info);
+		seq_printf(m, "%d.%03d ", index / 1000, index % 1000);
+	}
+
+	seq_putc(m, '\n');
+}
+
+/*
+ * Display unusable free space index
+ * XXX: Could be a lot more efficient, but it's not a critical path
+ */
+static int unusable_show(struct seq_file *m, void *arg)
+{
+	pg_data_t *pgdat = (pg_data_t *)arg;
+
+	/* check memoryless node */
+	if (!node_state(pgdat->node_id, N_HIGH_MEMORY))
+		return 0;
+
+	walk_zones_in_node(m, pgdat, unusable_show_print);
+
+	return 0;
+}
+
 static void pagetypeinfo_showfree_print(struct seq_file *m,
 					pg_data_t *pgdat, struct zone *zone)
 {
@@ -603,6 +703,25 @@ static const struct file_operations pagetypeinfo_file_ops = {
 	.release	= seq_release,
 };
 
+static const struct seq_operations unusable_op = {
+	.start	= frag_start,
+	.next	= frag_next,
+	.stop	= frag_stop,
+	.show	= unusable_show,
+};
+
+static int unusable_open(struct inode *inode, struct file *file)
+{
+	return seq_open(file, &unusable_op);
+}
+
+static const struct file_operations unusable_file_ops = {
+	.open		= unusable_open,
+	.read		= seq_read,
+	.llseek		= seq_lseek,
+	.release	= seq_release,
+};
+
 #ifdef CONFIG_ZONE_DMA
 #define TEXT_FOR_DMA(xx) xx "_dma",
 #else
@@ -947,6 +1066,7 @@ static int __init setup_vmstat(void)
 #ifdef CONFIG_PROC_FS
 	proc_create("buddyinfo", S_IRUGO, NULL, &fragmentation_file_operations);
 	proc_create("pagetypeinfo", S_IRUGO, NULL, &pagetypeinfo_file_ops);
+	proc_create("unusable_index", S_IRUGO, NULL, &unusable_file_ops);
 	proc_create("vmstat", S_IRUGO, NULL, &proc_vmstat_file_operations);
 	proc_create("zoneinfo", S_IRUGO, NULL, &proc_zoneinfo_file_operations);
 #endif
-- 
1.6.5