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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
rtc-starfire.c 
/* rtc-starfire.c: Starfire platform RTC driver.
 *
 * Copyright (C) 2008 David S. Miller <davem@davemloft.net>
 */

#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/init.h>
#include <linux/rtc.h>
#include <linux/platform_device.h>

#include <asm/oplib.h>

MODULE_AUTHOR("David S. Miller <davem@davemloft.net>");
MODULE_DESCRIPTION("Starfire RTC driver");
MODULE_LICENSE("GPL");

static u32 starfire_get_time(void)
{
	static char obp_gettod[32];
	static u32 unix_tod;

	sprintf(obp_gettod, "h# %08x unix-gettod",
		(unsigned int) (long) &unix_tod);
	prom_feval(obp_gettod);

	return unix_tod;
}

static int starfire_read_time(struct device *dev, struct rtc_time *tm)
{
	rtc_time_to_tm(starfire_get_time(), tm);
	return rtc_valid_tm(tm);
}

static const struct rtc_class_ops starfire_rtc_ops = {
	.read_time	= starfire_read_time,
};

static int __init starfire_rtc_probe(struct platform_device *pdev)
{
	struct rtc_device *rtc = rtc_device_register("starfire", &pdev->dev,
				     &starfire_rtc_ops, THIS_MODULE);
	if (IS_ERR(rtc))
		return PTR_ERR(rtc);

	platform_set_drvdata(pdev, rtc);

	return 0;
}

static int __exit starfire_rtc_remove(struct platform_device *pdev)
{
	struct rtc_device *rtc = platform_get_drvdata(pdev);

	rtc_device_unregister(rtc);

	return 0;
}

static struct platform_driver starfire_rtc_driver = {
	.driver		= {
		.name	= "rtc-starfire",
		.owner	= THIS_MODULE,
	},
	.remove		= __exit_p(starfire_rtc_remove),
};

static int __init starfire_rtc_init(void)
{
	return platform_driver_probe(&starfire_rtc_driver, starfire_rtc_probe);
}

static void __exit starfire_rtc_exit(void)
{
	platform_driver_unregister(&starfire_rtc_driver);
}

module_init(starfire_rtc_init);
module_exit(starfire_rtc_exit);
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