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Revision d7831a0bdf06b9f722b947bb0c205ff7d77cebd8 authored by Richard Kennedy on 30 June 2009, 18:41:35 UTC, committed by Linus Torvalds on 01 July 2009, 01:56:01 UTC 
mm: prevent balance_dirty_pages() from doing too much work
 
balance_dirty_pages can overreact and move all of the dirty pages to
writeback unnecessarily.

balance_dirty_pages makes its decision to throttle based on the number of
dirty plus writeback pages that are over the calculated limit,so it will
continue to move pages even when there are plenty of pages in writeback
and less than the threshold still dirty.

This allows it to overshoot its limits and move all the dirty pages to
writeback while waiting for the drives to catch up and empty the writeback
list.

A simple fio test easily demonstrates this problem.

fio --name=f1 --directory=/disk1 --size=2G -rw=write --name=f2 --directory=/disk2 --size=1G --rw=write --startdelay=10

This is the simplest fix I could find, but I'm not entirely sure that it
alone will be enough for all cases.  But it certainly is an improvement on
my desktop machine writing to 2 disks.

Do we need something more for machines with large arrays where
bdi_threshold * number_of_drives is greater than the dirty_ratio ?

Signed-off-by: Richard Kennedy <richard@rsk.demon.co.uk>
Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Jens Axboe <jens.axboe@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
1 parent df279ca
Raw File
dm-sysfs.c 
/*
 * Copyright (C) 2008 Red Hat, Inc. All rights reserved.
 *
 * This file is released under the GPL.
 */

#include <linux/sysfs.h>
#include <linux/dm-ioctl.h>
#include "dm.h"

struct dm_sysfs_attr {
	struct attribute attr;
	ssize_t (*show)(struct mapped_device *, char *);
	ssize_t (*store)(struct mapped_device *, char *);
};

#define DM_ATTR_RO(_name) \
struct dm_sysfs_attr dm_attr_##_name = \
	__ATTR(_name, S_IRUGO, dm_attr_##_name##_show, NULL)

static ssize_t dm_attr_show(struct kobject *kobj, struct attribute *attr,
			    char *page)
{
	struct dm_sysfs_attr *dm_attr;
	struct mapped_device *md;
	ssize_t ret;

	dm_attr = container_of(attr, struct dm_sysfs_attr, attr);
	if (!dm_attr->show)
		return -EIO;

	md = dm_get_from_kobject(kobj);
	if (!md)
		return -EINVAL;

	ret = dm_attr->show(md, page);
	dm_put(md);

	return ret;
}

static ssize_t dm_attr_name_show(struct mapped_device *md, char *buf)
{
	if (dm_copy_name_and_uuid(md, buf, NULL))
		return -EIO;

	strcat(buf, "\n");
	return strlen(buf);
}

static ssize_t dm_attr_uuid_show(struct mapped_device *md, char *buf)
{
	if (dm_copy_name_and_uuid(md, NULL, buf))
		return -EIO;

	strcat(buf, "\n");
	return strlen(buf);
}

static ssize_t dm_attr_suspended_show(struct mapped_device *md, char *buf)
{
	sprintf(buf, "%d\n", dm_suspended(md));

	return strlen(buf);
}

static DM_ATTR_RO(name);
static DM_ATTR_RO(uuid);
static DM_ATTR_RO(suspended);

static struct attribute *dm_attrs[] = {
	&dm_attr_name.attr,
	&dm_attr_uuid.attr,
	&dm_attr_suspended.attr,
	NULL,
};

static struct sysfs_ops dm_sysfs_ops = {
	.show	= dm_attr_show,
};

/*
 * dm kobject is embedded in mapped_device structure
 * no need to define release function here
 */
static struct kobj_type dm_ktype = {
	.sysfs_ops	= &dm_sysfs_ops,
	.default_attrs	= dm_attrs,
};

/*
 * Initialize kobj
 * because nobody using md yet, no need to call explicit dm_get/put
 */
int dm_sysfs_init(struct mapped_device *md)
{
	return kobject_init_and_add(dm_kobject(md), &dm_ktype,
				    &disk_to_dev(dm_disk(md))->kobj,
				    "%s", "dm");
}

/*
 * Remove kobj, called after all references removed
 */
void dm_sysfs_exit(struct mapped_device *md)
{
	kobject_put(dm_kobject(md));
}
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