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
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
mca-legacy.c
/* -*- mode: c; c-basic-offset: 8 -*- */
/*
* MCA bus support functions for legacy (2.4) API.
*
* Legacy API means the API that operates in terms of MCA slot number
*
* (C) 2002 James Bottomley <James.Bottomley@HansenPartnership.com>
*
**-----------------------------------------------------------------------------
**
** This program is free software; you can redistribute it and/or modify
** it under the terms of the GNU General Public License as published by
** the Free Software Foundation; either version 2 of the License, or
** (at your option) any later version.
**
** This program is distributed in the hope that it will be useful,
** but WITHOUT ANY WARRANTY; without even the implied warranty of
** MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
** GNU General Public License for more details.
**
** You should have received a copy of the GNU General Public License
** along with this program; if not, write to the Free Software
** Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
**
**-----------------------------------------------------------------------------
*/
#include <linux/module.h>
#include <linux/device.h>
#include <linux/mca-legacy.h>
#include <asm/io.h>
/* NOTE: This structure is stack allocated */
struct mca_find_adapter_info {
int id;
int slot;
struct mca_device *mca_dev;
};
/* The purpose of this iterator is to loop over all the devices and
* find the one with the smallest slot number that's just greater than
* or equal to the required slot with a matching id */
static int mca_find_adapter_callback(struct device *dev, void *data)
{
struct mca_find_adapter_info *info = data;
struct mca_device *mca_dev = to_mca_device(dev);
if(mca_dev->pos_id != info->id)
return 0;
if(mca_dev->slot < info->slot)
return 0;
if(!info->mca_dev || info->mca_dev->slot >= mca_dev->slot)
info->mca_dev = mca_dev;
return 0;
}
/**
* mca_find_adapter - scan for adapters
* @id: MCA identification to search for
* @start: starting slot
*
* Search the MCA configuration for adapters matching the 16bit
* ID given. The first time it should be called with start as zero
* and then further calls made passing the return value of the
* previous call until %MCA_NOTFOUND is returned.
*
* Disabled adapters are not reported.
*/
int mca_find_adapter(int id, int start)
{
struct mca_find_adapter_info info;
if(id == 0xffff)
return MCA_NOTFOUND;
info.slot = start;
info.id = id;
info.mca_dev = NULL;
for(;;) {
bus_for_each_dev(&mca_bus_type, NULL, &info, mca_find_adapter_callback);
if(info.mca_dev == NULL)
return MCA_NOTFOUND;
if(info.mca_dev->status != MCA_ADAPTER_DISABLED)
break;
/* OK, found adapter but it was disabled. Go around
* again, excluding the slot we just found */
info.slot = info.mca_dev->slot + 1;
info.mca_dev = NULL;
}
return info.mca_dev->slot;
}
EXPORT_SYMBOL(mca_find_adapter);
/*--------------------------------------------------------------------*/
/**
* mca_find_unused_adapter - scan for unused adapters
* @id: MCA identification to search for
* @start: starting slot
*
* Search the MCA configuration for adapters matching the 16bit
* ID given. The first time it should be called with start as zero
* and then further calls made passing the return value of the
* previous call until %MCA_NOTFOUND is returned.
*
* Adapters that have been claimed by drivers and those that
* are disabled are not reported. This function thus allows a driver
* to scan for further cards when some may already be driven.
*/
int mca_find_unused_adapter(int id, int start)
{
struct mca_find_adapter_info info = { 0 };
if (!MCA_bus || id == 0xffff)
return MCA_NOTFOUND;
info.slot = start;
info.id = id;
info.mca_dev = NULL;
for(;;) {
bus_for_each_dev(&mca_bus_type, NULL, &info, mca_find_adapter_callback);
if(info.mca_dev == NULL)
return MCA_NOTFOUND;
if(info.mca_dev->status != MCA_ADAPTER_DISABLED
&& !info.mca_dev->driver_loaded)
break;
/* OK, found adapter but it was disabled or already in
* use. Go around again, excluding the slot we just
* found */
info.slot = info.mca_dev->slot + 1;
info.mca_dev = NULL;
}
return info.mca_dev->slot;
}
EXPORT_SYMBOL(mca_find_unused_adapter);
/* NOTE: stack allocated structure */
struct mca_find_device_by_slot_info {
int slot;
struct mca_device *mca_dev;
};
static int mca_find_device_by_slot_callback(struct device *dev, void *data)
{
struct mca_find_device_by_slot_info *info = data;
struct mca_device *mca_dev = to_mca_device(dev);
if(mca_dev->slot == info->slot)
info->mca_dev = mca_dev;
return 0;
}
struct mca_device *mca_find_device_by_slot(int slot)
{
struct mca_find_device_by_slot_info info;
info.slot = slot;
info.mca_dev = NULL;
bus_for_each_dev(&mca_bus_type, NULL, &info, mca_find_device_by_slot_callback);
return info.mca_dev;
}
/**
* mca_read_stored_pos - read POS register from boot data
* @slot: slot number to read from
* @reg: register to read from
*
* Fetch a POS value that was stored at boot time by the kernel
* when it scanned the MCA space. The register value is returned.
* Missing or invalid registers report 0.
*/
unsigned char mca_read_stored_pos(int slot, int reg)
{
struct mca_device *mca_dev = mca_find_device_by_slot(slot);
if(!mca_dev)
return 0;
return mca_device_read_stored_pos(mca_dev, reg);
}
EXPORT_SYMBOL(mca_read_stored_pos);
/**
* mca_read_pos - read POS register from card
* @slot: slot number to read from
* @reg: register to read from
*
* Fetch a POS value directly from the hardware to obtain the
* current value. This is much slower than mca_read_stored_pos and
* may not be invoked from interrupt context. It handles the
* deep magic required for onboard devices transparently.
*/
unsigned char mca_read_pos(int slot, int reg)
{
struct mca_device *mca_dev = mca_find_device_by_slot(slot);
if(!mca_dev)
return 0;
return mca_device_read_pos(mca_dev, reg);
}
EXPORT_SYMBOL(mca_read_pos);
/**
* mca_write_pos - read POS register from card
* @slot: slot number to read from
* @reg: register to read from
* @byte: byte to write to the POS registers
*
* Store a POS value directly from the hardware. You should not
* normally need to use this function and should have a very good
* knowledge of MCA bus before you do so. Doing this wrongly can
* damage the hardware.
*
* This function may not be used from interrupt context.
*
* Note that this a technically a Bad Thing, as IBM tech stuff says
* you should only set POS values through their utilities.
* However, some devices such as the 3c523 recommend that you write
* back some data to make sure the configuration is consistent.
* I'd say that IBM is right, but I like my drivers to work.
*
* This function can't do checks to see if multiple devices end up
* with the same resources, so you might see magic smoke if someone
* screws up.
*/
void mca_write_pos(int slot, int reg, unsigned char byte)
{
struct mca_device *mca_dev = mca_find_device_by_slot(slot);
if(!mca_dev)
return;
mca_device_write_pos(mca_dev, reg, byte);
}
EXPORT_SYMBOL(mca_write_pos);
/**
* mca_set_adapter_name - Set the description of the card
* @slot: slot to name
* @name: text string for the namen
*
* This function sets the name reported via /proc for this
* adapter slot. This is for user information only. Setting a
* name deletes any previous name.
*/
void mca_set_adapter_name(int slot, char* name)
{
struct mca_device *mca_dev = mca_find_device_by_slot(slot);
if(!mca_dev)
return;
mca_device_set_name(mca_dev, name);
}
EXPORT_SYMBOL(mca_set_adapter_name);
/**
* mca_mark_as_used - claim an MCA device
* @slot: slot to claim
* FIXME: should we make this threadsafe
*
* Claim an MCA slot for a device driver. If the
* slot is already taken the function returns 1,
* if it is not taken it is claimed and 0 is
* returned.
*/
int mca_mark_as_used(int slot)
{
struct mca_device *mca_dev = mca_find_device_by_slot(slot);
if(!mca_dev)
/* FIXME: this is actually a severe error */
return 1;
if(mca_device_claimed(mca_dev))
return 1;
mca_device_set_claim(mca_dev, 1);
return 0;
}
EXPORT_SYMBOL(mca_mark_as_used);
/**
* mca_mark_as_unused - release an MCA device
* @slot: slot to claim
*
* Release the slot for other drives to use.
*/
void mca_mark_as_unused(int slot)
{
struct mca_device *mca_dev = mca_find_device_by_slot(slot);
if(!mca_dev)
return;
mca_device_set_claim(mca_dev, 0);
}
EXPORT_SYMBOL(mca_mark_as_unused);
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