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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>
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Raw File
sa1100_jornada720.c 
/*
 * drivers/pcmcia/sa1100_jornada720.c
 *
 * Jornada720 PCMCIA specific routines
 *
 */
#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/device.h>
#include <linux/errno.h>
#include <linux/init.h>

#include <mach/hardware.h>
#include <asm/hardware/sa1111.h>
#include <asm/mach-types.h>

#include "sa1111_generic.h"

#define SOCKET0_POWER   GPIO_GPIO0
#define SOCKET0_3V      GPIO_GPIO2
#define SOCKET1_POWER   (GPIO_GPIO1 | GPIO_GPIO3)
#warning *** Does SOCKET1_3V actually do anything?
#define SOCKET1_3V	GPIO_GPIO3

static int jornada720_pcmcia_hw_init(struct soc_pcmcia_socket *skt)
{
  /*
   * What is all this crap for?
   */
  GRER |= 0x00000002;
  /* Set GPIO_A<3:1> to be outputs for PCMCIA/CF power controller: */
  sa1111_set_io_dir(SA1111_DEV(skt->dev), GPIO_A0|GPIO_A1|GPIO_A2|GPIO_A3, 0, 0);
  sa1111_set_io(SA1111_DEV(skt->dev), GPIO_A0|GPIO_A1|GPIO_A2|GPIO_A3, 0);
  sa1111_set_sleep_io(SA1111_DEV(skt->dev), GPIO_A0|GPIO_A1|GPIO_A2|GPIO_A3, 0);

  return sa1111_pcmcia_hw_init(skt);
}

static int
jornada720_pcmcia_configure_socket(struct soc_pcmcia_socket *skt, const socket_state_t *state)
{
  unsigned int pa_dwr_mask, pa_dwr_set;
  int ret;

printk("%s(): config socket %d vcc %d vpp %d\n", __func__,
	skt->nr, state->Vcc, state->Vpp);

  switch (skt->nr) {
  case 0:
    pa_dwr_mask = SOCKET0_POWER | SOCKET0_3V;

    switch (state->Vcc) {
    default:
    case 0:	pa_dwr_set = 0;					break;
    case 33:	pa_dwr_set = SOCKET0_POWER | SOCKET0_3V;	break;
    case 50:	pa_dwr_set = SOCKET0_POWER;			break;
    }
    break;

  case 1:
    pa_dwr_mask = SOCKET1_POWER;

    switch (state->Vcc) {
    default:
    case 0:	pa_dwr_set = 0;					break;
    case 33:	pa_dwr_set = SOCKET1_POWER;			break;
    case 50:	pa_dwr_set = SOCKET1_POWER;			break;
    }
    break;

  default:
    return -1;
  }

  if (state->Vpp != state->Vcc && state->Vpp != 0) {
    printk(KERN_ERR "%s(): slot cannot support VPP %u\n",
	   __func__, state->Vpp);
    return -1;
  }

  ret = sa1111_pcmcia_configure_socket(skt, state);
  if (ret == 0) {
    unsigned long flags;

    local_irq_save(flags);
    sa1111_set_io(SA1111_DEV(skt->dev), pa_dwr_mask, pa_dwr_set);
    local_irq_restore(flags);
  }

  return ret;
}

static struct pcmcia_low_level jornada720_pcmcia_ops = {
  .owner		= THIS_MODULE,
  .hw_init		= jornada720_pcmcia_hw_init,
  .hw_shutdown		= sa1111_pcmcia_hw_shutdown,
  .socket_state		= sa1111_pcmcia_socket_state,
  .configure_socket	= jornada720_pcmcia_configure_socket,

  .socket_init		= sa1111_pcmcia_socket_init,
  .socket_suspend	= sa1111_pcmcia_socket_suspend,
};

int __devinit pcmcia_jornada720_init(struct device *dev)
{
	int ret = -ENODEV;

	if (machine_is_jornada720())
		ret = sa11xx_drv_pcmcia_probe(dev, &jornada720_pcmcia_ops, 0, 2);

	return ret;
}
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