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Commit f1a5ab12 authored by Mel Gorman's avatar Mel Gorman Committed by Linus Torvalds
Browse files

mm: export fragmentation index via debugfs 



The fragmentation fragmentation index, is only meaningful if an allocation
would fail and indicates what the failure is due to.  A value of -1 such
as in many of the examples above states that the allocation would succeed.
 If it would fail, the value is between 0 and 1.  A value tending towards
0 implies the allocation failed due to a lack of memory.  A value tending
towards 1 implies it failed due to external fragmentation.

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-zo basis via
/sys/kernel/debug/extfrag/extfrag_index

> cat /sys/kernel/debug/extfrag/extfrag_index
Node 0, zone      DMA -1.000 -1.000 -1.000 -1.000 -1.000 -1.000 -1.000 -1.00
Node 0, zone   Normal -1.000 -1.000 -1.000 -1.000 -1.000 -1.000 -1.000 0.954

Signed-off-by: default avatarMel Gorman <mel@csn.ul.ie>
Reviewed-by: default avatarMinchan Kim <minchan.kim@gmail.com>
Acked-by: default avatarRik van Riel <riel@redhat.com>
Reviewed-by: default avatarChristoph Lameter <cl@linux-foundation.org>
Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent d7a5752c

mm/vmstat.c

+84 −0
Original line number Diff line number Diff line
@@ -16,6 +16,7 @@ 
#include <linux/cpu.h>

#include <linux/vmstat.h>

#include <linux/sched.h>

#include <linux/math64.h>



#ifdef CONFIG_VM_EVENT_COUNTERS

DEFINE_PER_CPU(struct vm_event_state, vm_event_states) = {{0}};
@@ -420,6 +421,33 @@ static void fill_contig_page_info(struct zone *zone, 
						(order - suitable_order);

	}

}



/*

 * A fragmentation index only makes sense if an allocation of a requested

 * size would fail. If that is true, the fragmentation index indicates

 * whether external fragmentation or a lack of memory was the problem.

 * The value can be used to determine if page reclaim or compaction

 * should be used

 */

int fragmentation_index(unsigned int order, struct contig_page_info *info)

{

	unsigned long requested = 1UL << order;



	if (!info->free_blocks_total)

		return 0;



	/* Fragmentation index only makes sense when a request would fail */

	if (info->free_blocks_suitable)

		return -1000;



	/*

	 * Index is between 0 and 1 so return within 3 decimal places

	 *

	 * 0 => allocation would fail due to lack of memory

	 * 1 => allocation would fail due to fragmentation

	 */

	return 1000 - div_u64( (1000+(div_u64(info->free_pages * 1000ULL, requested))), info->free_blocks_total);

}

#endif



#if defined(CONFIG_PROC_FS) || defined(CONFIG_COMPACTION)
@@ -1087,6 +1115,58 @@ static const struct file_operations unusable_file_ops = { 
	.release	= seq_release,

};



static void extfrag_show_print(struct seq_file *m,

					pg_data_t *pgdat, struct zone *zone)

{

	unsigned int order;

	int index;



	/* Alloc on stack as interrupts are disabled for zone walk */

	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 = fragmentation_index(order, &info);

		seq_printf(m, "%d.%03d ", index / 1000, index % 1000);

	}



	seq_putc(m, '\n');

}



/*

 * Display fragmentation index for orders that allocations would fail for

 */

static int extfrag_show(struct seq_file *m, void *arg)

{

	pg_data_t *pgdat = (pg_data_t *)arg;



	walk_zones_in_node(m, pgdat, extfrag_show_print);



	return 0;

}



static const struct seq_operations extfrag_op = {

	.start	= frag_start,

	.next	= frag_next,

	.stop	= frag_stop,

	.show	= extfrag_show,

};



static int extfrag_open(struct inode *inode, struct file *file)

{

	return seq_open(file, &extfrag_op);

}



static const struct file_operations extfrag_file_ops = {

	.open		= extfrag_open,

	.read		= seq_read,

	.llseek		= seq_lseek,

	.release	= seq_release,

};



static int __init extfrag_debug_init(void)

{

	extfrag_debug_root = debugfs_create_dir("extfrag", NULL);
@@ -1097,6 +1177,10 @@ static int __init extfrag_debug_init(void) 
			extfrag_debug_root, NULL, &unusable_file_ops))

		return -ENOMEM;



	if (!debugfs_create_file("extfrag_index", 0444,

			extfrag_debug_root, NULL, &extfrag_file_ops))

		return -ENOMEM;



	return 0;

}