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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
input-compat.h 
#ifndef _INPUT_COMPAT_H
#define _INPUT_COMPAT_H

/*
 * 32bit compatibility wrappers for the input subsystem.
 *
 * Very heavily based on evdev.c - Copyright (c) 1999-2002 Vojtech Pavlik
 *
 * This program is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 as published by
 * the Free Software Foundation.
 */

#include <linux/compiler.h>
#include <linux/compat.h>
#include <linux/input.h>

#ifdef CONFIG_COMPAT

/* Note to the author of this code: did it ever occur to
   you why the ifdefs are needed? Think about it again. -AK */
#ifdef CONFIG_X86_64
#  define INPUT_COMPAT_TEST is_compat_task()
#elif defined(CONFIG_IA64)
#  define INPUT_COMPAT_TEST IS_IA32_PROCESS(task_pt_regs(current))
#elif defined(CONFIG_S390)
#  define INPUT_COMPAT_TEST test_thread_flag(TIF_31BIT)
#elif defined(CONFIG_MIPS)
#  define INPUT_COMPAT_TEST test_thread_flag(TIF_32BIT_ADDR)
#else
#  define INPUT_COMPAT_TEST test_thread_flag(TIF_32BIT)
#endif

struct input_event_compat {
	struct compat_timeval time;
	__u16 type;
	__u16 code;
	__s32 value;
};

struct ff_periodic_effect_compat {
	__u16 waveform;
	__u16 period;
	__s16 magnitude;
	__s16 offset;
	__u16 phase;

	struct ff_envelope envelope;

	__u32 custom_len;
	compat_uptr_t custom_data;
};

struct ff_effect_compat {
	__u16 type;
	__s16 id;
	__u16 direction;
	struct ff_trigger trigger;
	struct ff_replay replay;

	union {
		struct ff_constant_effect constant;
		struct ff_ramp_effect ramp;
		struct ff_periodic_effect_compat periodic;
		struct ff_condition_effect condition[2]; /* One for each axis */
		struct ff_rumble_effect rumble;
	} u;
};

static inline size_t input_event_size(void)
{
	return INPUT_COMPAT_TEST ?
		sizeof(struct input_event_compat) : sizeof(struct input_event);
}

#else

static inline size_t input_event_size(void)
{
	return sizeof(struct input_event);
}

#endif /* CONFIG_COMPAT */

int input_event_from_user(const char __user *buffer,
			 struct input_event *event);

int input_event_to_user(char __user *buffer,
			const struct input_event *event);

int input_ff_effect_from_user(const char __user *buffer, size_t size,
			      struct ff_effect *effect);

#endif /* _INPUT_COMPAT_H */
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