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>
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dm-exception-store.h
/*
* Copyright (C) 2001-2002 Sistina Software (UK) Limited.
* Copyright (C) 2008 Red Hat, Inc. All rights reserved.
*
* Device-mapper snapshot exception store.
*
* This file is released under the GPL.
*/
#ifndef _LINUX_DM_EXCEPTION_STORE
#define _LINUX_DM_EXCEPTION_STORE
#include <linux/blkdev.h>
#include <linux/device-mapper.h>
/*
* The snapshot code deals with largish chunks of the disk at a
* time. Typically 32k - 512k.
*/
typedef sector_t chunk_t;
/*
* An exception is used where an old chunk of data has been
* replaced by a new one.
* If chunk_t is 64 bits in size, the top 8 bits of new_chunk hold the number
* of chunks that follow contiguously. Remaining bits hold the number of the
* chunk within the device.
*/
struct dm_snap_exception {
struct list_head hash_list;
chunk_t old_chunk;
chunk_t new_chunk;
};
/*
* Abstraction to handle the meta/layout of exception stores (the
* COW device).
*/
struct dm_exception_store;
struct dm_exception_store_type {
const char *name;
struct module *module;
int (*ctr) (struct dm_exception_store *store,
unsigned argc, char **argv);
/*
* Destroys this object when you've finished with it.
*/
void (*dtr) (struct dm_exception_store *store);
/*
* The target shouldn't read the COW device until this is
* called. As exceptions are read from the COW, they are
* reported back via the callback.
*/
int (*read_metadata) (struct dm_exception_store *store,
int (*callback)(void *callback_context,
chunk_t old, chunk_t new),
void *callback_context);
/*
* Find somewhere to store the next exception.
*/
int (*prepare_exception) (struct dm_exception_store *store,
struct dm_snap_exception *e);
/*
* Update the metadata with this exception.
*/
void (*commit_exception) (struct dm_exception_store *store,
struct dm_snap_exception *e,
void (*callback) (void *, int success),
void *callback_context);
/*
* The snapshot is invalid, note this in the metadata.
*/
void (*drop_snapshot) (struct dm_exception_store *store);
unsigned (*status) (struct dm_exception_store *store,
status_type_t status, char *result,
unsigned maxlen);
/*
* Return how full the snapshot is.
*/
void (*fraction_full) (struct dm_exception_store *store,
sector_t *numerator,
sector_t *denominator);
/* For internal device-mapper use only. */
struct list_head list;
};
struct dm_exception_store {
struct dm_exception_store_type *type;
struct dm_target *ti;
struct dm_dev *cow;
/* Size of data blocks saved - must be a power of 2 */
chunk_t chunk_size;
chunk_t chunk_mask;
chunk_t chunk_shift;
void *context;
};
/*
* Funtions to manipulate consecutive chunks
*/
# if defined(CONFIG_LBDAF) || (BITS_PER_LONG == 64)
# define DM_CHUNK_CONSECUTIVE_BITS 8
# define DM_CHUNK_NUMBER_BITS 56
static inline chunk_t dm_chunk_number(chunk_t chunk)
{
return chunk & (chunk_t)((1ULL << DM_CHUNK_NUMBER_BITS) - 1ULL);
}
static inline unsigned dm_consecutive_chunk_count(struct dm_snap_exception *e)
{
return e->new_chunk >> DM_CHUNK_NUMBER_BITS;
}
static inline void dm_consecutive_chunk_count_inc(struct dm_snap_exception *e)
{
e->new_chunk += (1ULL << DM_CHUNK_NUMBER_BITS);
BUG_ON(!dm_consecutive_chunk_count(e));
}
# else
# define DM_CHUNK_CONSECUTIVE_BITS 0
static inline chunk_t dm_chunk_number(chunk_t chunk)
{
return chunk;
}
static inline unsigned dm_consecutive_chunk_count(struct dm_snap_exception *e)
{
return 0;
}
static inline void dm_consecutive_chunk_count_inc(struct dm_snap_exception *e)
{
}
# endif
/*
* Return the number of sectors in the device.
*/
static inline sector_t get_dev_size(struct block_device *bdev)
{
return i_size_read(bdev->bd_inode) >> SECTOR_SHIFT;
}
static inline chunk_t sector_to_chunk(struct dm_exception_store *store,
sector_t sector)
{
return (sector & ~store->chunk_mask) >> store->chunk_shift;
}
int dm_exception_store_type_register(struct dm_exception_store_type *type);
int dm_exception_store_type_unregister(struct dm_exception_store_type *type);
int dm_exception_store_create(struct dm_target *ti, int argc, char **argv,
unsigned *args_used,
struct dm_exception_store **store);
void dm_exception_store_destroy(struct dm_exception_store *store);
int dm_exception_store_init(void);
void dm_exception_store_exit(void);
/*
* Two exception store implementations.
*/
int dm_persistent_snapshot_init(void);
void dm_persistent_snapshot_exit(void);
int dm_transient_snapshot_init(void);
void dm_transient_snapshot_exit(void);
#endif /* _LINUX_DM_EXCEPTION_STORE */
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