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Otherwise, for sequential workloads, the dm_request_fn can allow excessive request merging at the expense of increased service time. Add a per-device sysfs attribute to allow the user to control how long a request, that is a reasonable merge candidate, can be queued on the request queue. The resolution of this request dispatch deadline is in microseconds (ranging from 1 to 100000 usecs), to set a 20us deadline: echo 20 > /sys/block/dm-7/dm/rq_based_seq_io_merge_deadline The dm_request_fn's merge heuristic and associated extra accounting is disabled by default (rq_based_seq_io_merge_deadline is 0). This sysfs attribute is not applicable to bio-based DM devices so it will only ever report 0 for them. By allowing a request to remain on the queue it will block others requests on the queue. But introducing a short dequeue delay has proven very effective at enabling certain sequential IO workloads on really fast, yet IOPS constrained, devices to build up slightly larger IOs -- yielding 90+% throughput improvements. Having precise control over the time taken to wait for larger requests to build affords control beyond that of waiting for certain IO sizes to accumulate (which would require a deadline anyway). This knob will only ever make sense with sequential IO workloads and the particular value used is storage configuration specific. Given the expected niche use-case for when this knob is useful it has been deemed acceptable to expose this relatively crude method for crafting optimal IO on specific storage -- especially given the solution is simple yet effective. In the context of DM multipath, it is advisable to tune this sysfs attribute to a value that offers the best performance for the common case (e.g. if 4 paths are expected active, tune for that; if paths fail then performance may be slightly reduced). Alternatives were explored to have request-based DM autotune this value (e.g. if/when paths fail) but they were quickly deemed too fragile and complex to warrant further design and development time. If this problem proves more common as faster storage emerges we'll have to look at elevating a generic solution into the block core. Tested-by: Shiva Krishna Merla <shivakrishna.merla@netapp.com> Signed-off-by: Mike Snitzer <snitzer@redhat.com>
242 lines
7.1 KiB
C
242 lines
7.1 KiB
C
/*
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* Internal header file for device mapper
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*
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* Copyright (C) 2001, 2002 Sistina Software
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* Copyright (C) 2004-2006 Red Hat, Inc. All rights reserved.
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*
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* This file is released under the LGPL.
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*/
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#ifndef DM_INTERNAL_H
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#define DM_INTERNAL_H
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#include <linux/fs.h>
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#include <linux/device-mapper.h>
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#include <linux/list.h>
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#include <linux/blkdev.h>
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#include <linux/hdreg.h>
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#include <linux/completion.h>
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#include <linux/kobject.h>
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#include "dm-stats.h"
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/*
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* Suspend feature flags
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*/
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#define DM_SUSPEND_LOCKFS_FLAG (1 << 0)
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#define DM_SUSPEND_NOFLUSH_FLAG (1 << 1)
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/*
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* Status feature flags
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*/
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#define DM_STATUS_NOFLUSH_FLAG (1 << 0)
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/*
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* Type of table and mapped_device's mempool
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*/
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#define DM_TYPE_NONE 0
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#define DM_TYPE_BIO_BASED 1
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#define DM_TYPE_REQUEST_BASED 2
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#define DM_TYPE_MQ_REQUEST_BASED 3
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/*
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* List of devices that a metadevice uses and should open/close.
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*/
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struct dm_dev_internal {
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struct list_head list;
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atomic_t count;
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struct dm_dev *dm_dev;
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};
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struct dm_table;
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struct dm_md_mempools;
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/*-----------------------------------------------------------------
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* Internal table functions.
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*---------------------------------------------------------------*/
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void dm_table_destroy(struct dm_table *t);
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void dm_table_event_callback(struct dm_table *t,
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void (*fn)(void *), void *context);
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struct dm_target *dm_table_get_target(struct dm_table *t, unsigned int index);
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struct dm_target *dm_table_find_target(struct dm_table *t, sector_t sector);
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bool dm_table_has_no_data_devices(struct dm_table *table);
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int dm_calculate_queue_limits(struct dm_table *table,
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struct queue_limits *limits);
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void dm_table_set_restrictions(struct dm_table *t, struct request_queue *q,
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struct queue_limits *limits);
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struct list_head *dm_table_get_devices(struct dm_table *t);
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void dm_table_presuspend_targets(struct dm_table *t);
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void dm_table_presuspend_undo_targets(struct dm_table *t);
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void dm_table_postsuspend_targets(struct dm_table *t);
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int dm_table_resume_targets(struct dm_table *t);
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int dm_table_any_congested(struct dm_table *t, int bdi_bits);
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unsigned dm_table_get_type(struct dm_table *t);
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struct target_type *dm_table_get_immutable_target_type(struct dm_table *t);
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bool dm_table_request_based(struct dm_table *t);
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bool dm_table_mq_request_based(struct dm_table *t);
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void dm_table_free_md_mempools(struct dm_table *t);
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struct dm_md_mempools *dm_table_get_md_mempools(struct dm_table *t);
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int dm_queue_merge_is_compulsory(struct request_queue *q);
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void dm_lock_md_type(struct mapped_device *md);
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void dm_unlock_md_type(struct mapped_device *md);
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void dm_set_md_type(struct mapped_device *md, unsigned type);
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unsigned dm_get_md_type(struct mapped_device *md);
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struct target_type *dm_get_immutable_target_type(struct mapped_device *md);
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int dm_setup_md_queue(struct mapped_device *md);
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/*
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* To check the return value from dm_table_find_target().
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*/
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#define dm_target_is_valid(t) ((t)->table)
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/*
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* To check whether the target type is bio-based or not (request-based).
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*/
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#define dm_target_bio_based(t) ((t)->type->map != NULL)
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/*
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* To check whether the target type is request-based or not (bio-based).
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*/
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#define dm_target_request_based(t) (((t)->type->map_rq != NULL) || \
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((t)->type->clone_and_map_rq != NULL))
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/*
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* To check whether the target type is a hybrid (capable of being
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* either request-based or bio-based).
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*/
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#define dm_target_hybrid(t) (dm_target_bio_based(t) && dm_target_request_based(t))
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/*-----------------------------------------------------------------
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* A registry of target types.
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*---------------------------------------------------------------*/
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int dm_target_init(void);
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void dm_target_exit(void);
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struct target_type *dm_get_target_type(const char *name);
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void dm_put_target_type(struct target_type *tt);
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int dm_target_iterate(void (*iter_func)(struct target_type *tt,
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void *param), void *param);
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int dm_split_args(int *argc, char ***argvp, char *input);
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/*
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* Is this mapped_device being deleted?
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*/
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int dm_deleting_md(struct mapped_device *md);
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/*
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* Is this mapped_device suspended?
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*/
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int dm_suspended_md(struct mapped_device *md);
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/*
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* Internal suspend and resume methods.
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*/
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int dm_suspended_internally_md(struct mapped_device *md);
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void dm_internal_suspend_fast(struct mapped_device *md);
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void dm_internal_resume_fast(struct mapped_device *md);
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void dm_internal_suspend_noflush(struct mapped_device *md);
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void dm_internal_resume(struct mapped_device *md);
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/*
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* Test if the device is scheduled for deferred remove.
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*/
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int dm_test_deferred_remove_flag(struct mapped_device *md);
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/*
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* Try to remove devices marked for deferred removal.
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*/
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void dm_deferred_remove(void);
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/*
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* The device-mapper can be driven through one of two interfaces;
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* ioctl or filesystem, depending which patch you have applied.
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*/
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int dm_interface_init(void);
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void dm_interface_exit(void);
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/*
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* sysfs interface
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*/
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struct dm_kobject_holder {
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struct kobject kobj;
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struct completion completion;
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};
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static inline struct completion *dm_get_completion_from_kobject(struct kobject *kobj)
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{
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return &container_of(kobj, struct dm_kobject_holder, kobj)->completion;
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}
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int dm_sysfs_init(struct mapped_device *md);
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void dm_sysfs_exit(struct mapped_device *md);
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struct kobject *dm_kobject(struct mapped_device *md);
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struct mapped_device *dm_get_from_kobject(struct kobject *kobj);
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/*
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* The kobject helper
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*/
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void dm_kobject_release(struct kobject *kobj);
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/*
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* Targets for linear and striped mappings
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*/
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int dm_linear_init(void);
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void dm_linear_exit(void);
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int dm_stripe_init(void);
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void dm_stripe_exit(void);
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/*
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* mapped_device operations
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*/
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void dm_destroy(struct mapped_device *md);
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void dm_destroy_immediate(struct mapped_device *md);
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int dm_open_count(struct mapped_device *md);
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int dm_lock_for_deletion(struct mapped_device *md, bool mark_deferred, bool only_deferred);
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int dm_cancel_deferred_remove(struct mapped_device *md);
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int dm_request_based(struct mapped_device *md);
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sector_t dm_get_size(struct mapped_device *md);
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struct request_queue *dm_get_md_queue(struct mapped_device *md);
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int dm_get_table_device(struct mapped_device *md, dev_t dev, fmode_t mode,
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struct dm_dev **result);
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void dm_put_table_device(struct mapped_device *md, struct dm_dev *d);
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struct dm_stats *dm_get_stats(struct mapped_device *md);
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int dm_kobject_uevent(struct mapped_device *md, enum kobject_action action,
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unsigned cookie);
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void dm_internal_suspend(struct mapped_device *md);
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void dm_internal_resume(struct mapped_device *md);
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int dm_io_init(void);
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void dm_io_exit(void);
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int dm_kcopyd_init(void);
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void dm_kcopyd_exit(void);
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/*
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* Mempool operations
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*/
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struct dm_md_mempools *dm_alloc_md_mempools(unsigned type, unsigned integrity, unsigned per_bio_data_size);
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void dm_free_md_mempools(struct dm_md_mempools *pools);
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/*
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* Helpers that are used by DM core
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*/
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unsigned dm_get_reserved_bio_based_ios(void);
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unsigned dm_get_reserved_rq_based_ios(void);
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static inline bool dm_message_test_buffer_overflow(char *result, unsigned maxlen)
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{
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return !maxlen || strlen(result) + 1 >= maxlen;
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}
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ssize_t dm_attr_rq_based_seq_io_merge_deadline_show(struct mapped_device *md, char *buf);
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ssize_t dm_attr_rq_based_seq_io_merge_deadline_store(struct mapped_device *md,
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const char *buf, size_t count);
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#endif
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