1 files changed, 988 insertions, 0 deletions

diff --git a/drivers/md/dm-kcopyd.c b/drivers/md/dm-kcopyd.c
new file mode 100644
index 000000000..0ef78e56a
--- /dev/null
+++ b/drivers/md/dm-kcopyd.c
@@ -0,0 +1,988 @@
+/*
+ * Copyright (C) 2002 Sistina Software (UK) Limited.
+ * Copyright (C) 2006 Red Hat GmbH
+ *
+ * This file is released under the GPL.
+ *
+ * Kcopyd provides a simple interface for copying an area of one
+ * block-device to one or more other block-devices, with an asynchronous
+ * completion notification.
+ */
+
+#include <linux/types.h>
+#include <linux/atomic.h>
+#include <linux/blkdev.h>
+#include <linux/fs.h>
+#include <linux/init.h>
+#include <linux/list.h>
+#include <linux/mempool.h>
+#include <linux/module.h>
+#include <linux/pagemap.h>
+#include <linux/slab.h>
+#include <linux/vmalloc.h>
+#include <linux/workqueue.h>
+#include <linux/mutex.h>
+#include <linux/delay.h>
+#include <linux/device-mapper.h>
+#include <linux/dm-kcopyd.h>
+
+#include "dm-core.h"
+
+#define SPLIT_COUNT	8
+#define MIN_JOBS	8
+
+#define DEFAULT_SUB_JOB_SIZE_KB 512
+#define MAX_SUB_JOB_SIZE_KB     1024
+
+static unsigned int kcopyd_subjob_size_kb = DEFAULT_SUB_JOB_SIZE_KB;
+
+module_param(kcopyd_subjob_size_kb, uint, S_IRUGO | S_IWUSR);
+MODULE_PARM_DESC(kcopyd_subjob_size_kb, "Sub-job size for dm-kcopyd clients");
+
+static unsigned int dm_get_kcopyd_subjob_size(void)
+{
+	unsigned int sub_job_size_kb;
+
+	sub_job_size_kb = __dm_get_module_param(&kcopyd_subjob_size_kb,
+						DEFAULT_SUB_JOB_SIZE_KB,
+						MAX_SUB_JOB_SIZE_KB);
+
+	return sub_job_size_kb << 1;
+}
+
+/*-----------------------------------------------------------------
+ * Each kcopyd client has its own little pool of preallocated
+ * pages for kcopyd io.
+ *---------------------------------------------------------------*/
+struct dm_kcopyd_client {
+	struct page_list *pages;
+	unsigned int nr_reserved_pages;
+	unsigned int nr_free_pages;
+	unsigned int sub_job_size;
+
+	struct dm_io_client *io_client;
+
+	wait_queue_head_t destroyq;
+
+	mempool_t job_pool;
+
+	struct workqueue_struct *kcopyd_wq;
+	struct work_struct kcopyd_work;
+
+	struct dm_kcopyd_throttle *throttle;
+
+	atomic_t nr_jobs;
+
+/*
+ * We maintain four lists of jobs:
+ *
+ * i)   jobs waiting for pages
+ * ii)  jobs that have pages, and are waiting for the io to be issued.
+ * iii) jobs that don't need to do any IO and just run a callback
+ * iv) jobs that have completed.
+ *
+ * All four of these are protected by job_lock.
+ */
+	spinlock_t job_lock;
+	struct list_head callback_jobs;
+	struct list_head complete_jobs;
+	struct list_head io_jobs;
+	struct list_head pages_jobs;
+};
+
+static struct page_list zero_page_list;
+
+static DEFINE_SPINLOCK(throttle_spinlock);
+
+/*
+ * IO/IDLE accounting slowly decays after (1 << ACCOUNT_INTERVAL_SHIFT) period.
+ * When total_period >= (1 << ACCOUNT_INTERVAL_SHIFT) the counters are divided
+ * by 2.
+ */
+#define ACCOUNT_INTERVAL_SHIFT		SHIFT_HZ
+
+/*
+ * Sleep this number of milliseconds.
+ *
+ * The value was decided experimentally.
+ * Smaller values seem to cause an increased copy rate above the limit.
+ * The reason for this is unknown but possibly due to jiffies rounding errors
+ * or read/write cache inside the disk.
+ */
+#define SLEEP_MSEC			100
+
+/*
+ * Maximum number of sleep events. There is a theoretical livelock if more
+ * kcopyd clients do work simultaneously which this limit avoids.
+ */
+#define MAX_SLEEPS			10
+
+static void io_job_start(struct dm_kcopyd_throttle *t)
+{
+	unsigned int throttle, now, difference;
+	int slept = 0, skew;
+
+	if (unlikely(!t))
+		return;
+
+try_again:
+	spin_lock_irq(&throttle_spinlock);
+
+	throttle = READ_ONCE(t->throttle);
+
+	if (likely(throttle >= 100))
+		goto skip_limit;
+
+	now = jiffies;
+	difference = now - t->last_jiffies;
+	t->last_jiffies = now;
+	if (t->num_io_jobs)
+		t->io_period += difference;
+	t->total_period += difference;
+
+	/*
+	 * Maintain sane values if we got a temporary overflow.
+	 */
+	if (unlikely(t->io_period > t->total_period))
+		t->io_period = t->total_period;
+
+	if (unlikely(t->total_period >= (1 << ACCOUNT_INTERVAL_SHIFT))) {
+		int shift = fls(t->total_period >> ACCOUNT_INTERVAL_SHIFT);
+		t->total_period >>= shift;
+		t->io_period >>= shift;
+	}
+
+	skew = t->io_period - throttle * t->total_period / 100;
+
+	if (unlikely(skew > 0) && slept < MAX_SLEEPS) {
+		slept++;
+		spin_unlock_irq(&throttle_spinlock);
+		msleep(SLEEP_MSEC);
+		goto try_again;
+	}
+
+skip_limit:
+	t->num_io_jobs++;
+
+	spin_unlock_irq(&throttle_spinlock);
+}
+
+static void io_job_finish(struct dm_kcopyd_throttle *t)
+{
+	unsigned long flags;
+
+	if (unlikely(!t))
+		return;
+
+	spin_lock_irqsave(&throttle_spinlock, flags);
+
+	t->num_io_jobs--;
+
+	if (likely(READ_ONCE(t->throttle) >= 100))
+		goto skip_limit;
+
+	if (!t->num_io_jobs) {
+		unsigned int now, difference;
+
+		now = jiffies;
+		difference = now - t->last_jiffies;
+		t->last_jiffies = now;
+
+		t->io_period += difference;
+		t->total_period += difference;
+
+		/*
+		 * Maintain sane values if we got a temporary overflow.
+		 */
+		if (unlikely(t->io_period > t->total_period))
+			t->io_period = t->total_period;
+	}
+
+skip_limit:
+	spin_unlock_irqrestore(&throttle_spinlock, flags);
+}
+
+
+static void wake(struct dm_kcopyd_client *kc)
+{
+	queue_work(kc->kcopyd_wq, &kc->kcopyd_work);
+}
+
+/*
+ * Obtain one page for the use of kcopyd.
+ */
+static struct page_list *alloc_pl(gfp_t gfp)
+{
+	struct page_list *pl;
+
+	pl = kmalloc(sizeof(*pl), gfp);
+	if (!pl)
+		return NULL;
+
+	pl->page = alloc_page(gfp | __GFP_HIGHMEM);
+	if (!pl->page) {
+		kfree(pl);
+		return NULL;
+	}
+
+	return pl;
+}
+
+static void free_pl(struct page_list *pl)
+{
+	__free_page(pl->page);
+	kfree(pl);
+}
+
+/*
+ * Add the provided pages to a client's free page list, releasing
+ * back to the system any beyond the reserved_pages limit.
+ */
+static void kcopyd_put_pages(struct dm_kcopyd_client *kc, struct page_list *pl)
+{
+	struct page_list *next;
+
+	do {
+		next = pl->next;
+
+		if (kc->nr_free_pages >= kc->nr_reserved_pages)
+			free_pl(pl);
+		else {
+			pl->next = kc->pages;
+			kc->pages = pl;
+			kc->nr_free_pages++;
+		}
+
+		pl = next;
+	} while (pl);
+}
+
+static int kcopyd_get_pages(struct dm_kcopyd_client *kc,
+			    unsigned int nr, struct page_list **pages)
+{
+	struct page_list *pl;
+
+	*pages = NULL;
+
+	do {
+		pl = alloc_pl(__GFP_NOWARN | __GFP_NORETRY | __GFP_KSWAPD_RECLAIM);
+		if (unlikely(!pl)) {
+			/* Use reserved pages */
+			pl = kc->pages;
+			if (unlikely(!pl))
+				goto out_of_memory;
+			kc->pages = pl->next;
+			kc->nr_free_pages--;
+		}
+		pl->next = *pages;
+		*pages = pl;
+	} while (--nr);
+
+	return 0;
+
+out_of_memory:
+	if (*pages)
+		kcopyd_put_pages(kc, *pages);
+	return -ENOMEM;
+}
+
+/*
+ * These three functions resize the page pool.
+ */
+static void drop_pages(struct page_list *pl)
+{
+	struct page_list *next;
+
+	while (pl) {
+		next = pl->next;
+		free_pl(pl);
+		pl = next;
+	}
+}
+
+/*
+ * Allocate and reserve nr_pages for the use of a specific client.
+ */
+static int client_reserve_pages(struct dm_kcopyd_client *kc, unsigned int nr_pages)
+{
+	unsigned int i;
+	struct page_list *pl = NULL, *next;
+
+	for (i = 0; i < nr_pages; i++) {
+		next = alloc_pl(GFP_KERNEL);
+		if (!next) {
+			if (pl)
+				drop_pages(pl);
+			return -ENOMEM;
+		}
+		next->next = pl;
+		pl = next;
+	}
+
+	kc->nr_reserved_pages += nr_pages;
+	kcopyd_put_pages(kc, pl);
+
+	return 0;
+}
+
+static void client_free_pages(struct dm_kcopyd_client *kc)
+{
+	BUG_ON(kc->nr_free_pages != kc->nr_reserved_pages);
+	drop_pages(kc->pages);
+	kc->pages = NULL;
+	kc->nr_free_pages = kc->nr_reserved_pages = 0;
+}
+
+/*-----------------------------------------------------------------
+ * kcopyd_jobs need to be allocated by the *clients* of kcopyd,
+ * for this reason we use a mempool to prevent the client from
+ * ever having to do io (which could cause a deadlock).
+ *---------------------------------------------------------------*/
+struct kcopyd_job {
+	struct dm_kcopyd_client *kc;
+	struct list_head list;
+	unsigned int flags;
+
+	/*
+	 * Error state of the job.
+	 */
+	int read_err;
+	unsigned long write_err;
+
+	/*
+	 * REQ_OP_READ, REQ_OP_WRITE or REQ_OP_WRITE_ZEROES.
+	 */
+	enum req_op op;
+	struct dm_io_region source;
+
+	/*
+	 * The destinations for the transfer.
+	 */
+	unsigned int num_dests;
+	struct dm_io_region dests[DM_KCOPYD_MAX_REGIONS];
+
+	struct page_list *pages;
+
+	/*
+	 * Set this to ensure you are notified when the job has
+	 * completed.  'context' is for callback to use.
+	 */
+	dm_kcopyd_notify_fn fn;
+	void *context;
+
+	/*
+	 * These fields are only used if the job has been split
+	 * into more manageable parts.
+	 */
+	struct mutex lock;
+	atomic_t sub_jobs;
+	sector_t progress;
+	sector_t write_offset;
+
+	struct kcopyd_job *master_job;
+};
+
+static struct kmem_cache *_job_cache;
+
+int __init dm_kcopyd_init(void)
+{
+	_job_cache = kmem_cache_create("kcopyd_job",
+				sizeof(struct kcopyd_job) * (SPLIT_COUNT + 1),
+				__alignof__(struct kcopyd_job), 0, NULL);
+	if (!_job_cache)
+		return -ENOMEM;
+
+	zero_page_list.next = &zero_page_list;
+	zero_page_list.page = ZERO_PAGE(0);
+
+	return 0;
+}
+
+void dm_kcopyd_exit(void)
+{
+	kmem_cache_destroy(_job_cache);
+	_job_cache = NULL;
+}
+
+/*
+ * Functions to push and pop a job onto the head of a given job
+ * list.
+ */
+static struct kcopyd_job *pop_io_job(struct list_head *jobs,
+				     struct dm_kcopyd_client *kc)
+{
+	struct kcopyd_job *job;
+
+	/*
+	 * For I/O jobs, pop any read, any write without sequential write
+	 * constraint and sequential writes that are at the right position.
+	 */
+	list_for_each_entry(job, jobs, list) {
+		if (job->op == REQ_OP_READ ||
+		    !(job->flags & BIT(DM_KCOPYD_WRITE_SEQ))) {
+			list_del(&job->list);
+			return job;
+		}
+
+		if (job->write_offset == job->master_job->write_offset) {
+			job->master_job->write_offset += job->source.count;
+			list_del(&job->list);
+			return job;
+		}
+	}
+
+	return NULL;
+}
+
+static struct kcopyd_job *pop(struct list_head *jobs,
+			      struct dm_kcopyd_client *kc)
+{
+	struct kcopyd_job *job = NULL;
+
+	spin_lock_irq(&kc->job_lock);
+
+	if (!list_empty(jobs)) {
+		if (jobs == &kc->io_jobs)
+			job = pop_io_job(jobs, kc);
+		else {
+			job = list_entry(jobs->next, struct kcopyd_job, list);
+			list_del(&job->list);
+		}
+	}
+	spin_unlock_irq(&kc->job_lock);
+
+	return job;
+}
+
+static void push(struct list_head *jobs, struct kcopyd_job *job)
+{
+	unsigned long flags;
+	struct dm_kcopyd_client *kc = job->kc;
+
+	spin_lock_irqsave(&kc->job_lock, flags);
+	list_add_tail(&job->list, jobs);
+	spin_unlock_irqrestore(&kc->job_lock, flags);
+}
+
+
+static void push_head(struct list_head *jobs, struct kcopyd_job *job)
+{
+	struct dm_kcopyd_client *kc = job->kc;
+
+	spin_lock_irq(&kc->job_lock);
+	list_add(&job->list, jobs);
+	spin_unlock_irq(&kc->job_lock);
+}
+
+/*
+ * These three functions process 1 item from the corresponding
+ * job list.
+ *
+ * They return:
+ * < 0: error
+ *   0: success
+ * > 0: can't process yet.
+ */
+static int run_complete_job(struct kcopyd_job *job)
+{
+	void *context = job->context;
+	int read_err = job->read_err;
+	unsigned long write_err = job->write_err;
+	dm_kcopyd_notify_fn fn = job->fn;
+	struct dm_kcopyd_client *kc = job->kc;
+
+	if (job->pages && job->pages != &zero_page_list)
+		kcopyd_put_pages(kc, job->pages);
+	/*
+	 * If this is the master job, the sub jobs have already
+	 * completed so we can free everything.
+	 */
+	if (job->master_job == job) {
+		mutex_destroy(&job->lock);
+		mempool_free(job, &kc->job_pool);
+	}
+	fn(read_err, write_err, context);
+
+	if (atomic_dec_and_test(&kc->nr_jobs))
+		wake_up(&kc->destroyq);
+
+	cond_resched();
+
+	return 0;
+}
+
+static void complete_io(unsigned long error, void *context)
+{
+	struct kcopyd_job *job = (struct kcopyd_job *) context;
+	struct dm_kcopyd_client *kc = job->kc;
+
+	io_job_finish(kc->throttle);
+
+	if (error) {
+		if (op_is_write(job->op))
+			job->write_err |= error;
+		else
+			job->read_err = 1;
+
+		if (!(job->flags & BIT(DM_KCOPYD_IGNORE_ERROR))) {
+			push(&kc->complete_jobs, job);
+			wake(kc);
+			return;
+		}
+	}
+
+	if (op_is_write(job->op))
+		push(&kc->complete_jobs, job);
+
+	else {
+		job->op = REQ_OP_WRITE;
+		push(&kc->io_jobs, job);
+	}
+
+	wake(kc);
+}
+
+/*
+ * Request io on as many buffer heads as we can currently get for
+ * a particular job.
+ */
+static int run_io_job(struct kcopyd_job *job)
+{
+	int r;
+	struct dm_io_request io_req = {
+		.bi_opf = job->op,
+		.mem.type = DM_IO_PAGE_LIST,
+		.mem.ptr.pl = job->pages,
+		.mem.offset = 0,
+		.notify.fn = complete_io,
+		.notify.context = job,
+		.client = job->kc->io_client,
+	};
+
+	/*
+	 * If we need to write sequentially and some reads or writes failed,
+	 * no point in continuing.
+	 */
+	if (job->flags & BIT(DM_KCOPYD_WRITE_SEQ) &&
+	    job->master_job->write_err) {
+		job->write_err = job->master_job->write_err;
+		return -EIO;
+	}
+
+	io_job_start(job->kc->throttle);
+
+	if (job->op == REQ_OP_READ)
+		r = dm_io(&io_req, 1, &job->source, NULL);
+	else
+		r = dm_io(&io_req, job->num_dests, job->dests, NULL);
+
+	return r;
+}
+
+static int run_pages_job(struct kcopyd_job *job)
+{
+	int r;
+	unsigned int nr_pages = dm_div_up(job->dests[0].count, PAGE_SIZE >> 9);
+
+	r = kcopyd_get_pages(job->kc, nr_pages, &job->pages);
+	if (!r) {
+		/* this job is ready for io */
+		push(&job->kc->io_jobs, job);
+		return 0;
+	}
+
+	if (r == -ENOMEM)
+		/* can't complete now */
+		return 1;
+
+	return r;
+}
+
+/*
+ * Run through a list for as long as possible.  Returns the count
+ * of successful jobs.
+ */
+static int process_jobs(struct list_head *jobs, struct dm_kcopyd_client *kc,
+			int (*fn) (struct kcopyd_job *))
+{
+	struct kcopyd_job *job;
+	int r, count = 0;
+
+	while ((job = pop(jobs, kc))) {
+
+		r = fn(job);
+
+		if (r < 0) {
+			/* error this rogue job */
+			if (op_is_write(job->op))
+				job->write_err = (unsigned long) -1L;
+			else
+				job->read_err = 1;
+			push(&kc->complete_jobs, job);
+			wake(kc);
+			break;
+		}
+
+		if (r > 0) {
+			/*
+			 * We couldn't service this job ATM, so
+			 * push this job back onto the list.
+			 */
+			push_head(jobs, job);
+			break;
+		}
+
+		count++;
+	}
+
+	return count;
+}
+
+/*
+ * kcopyd does this every time it's woken up.
+ */
+static void do_work(struct work_struct *work)
+{
+	struct dm_kcopyd_client *kc = container_of(work,
+					struct dm_kcopyd_client, kcopyd_work);
+	struct blk_plug plug;
+
+	/*
+	 * The order that these are called is *very* important.
+	 * complete jobs can free some pages for pages jobs.
+	 * Pages jobs when successful will jump onto the io jobs
+	 * list.  io jobs call wake when they complete and it all
+	 * starts again.
+	 */
+	spin_lock_irq(&kc->job_lock);
+	list_splice_tail_init(&kc->callback_jobs, &kc->complete_jobs);
+	spin_unlock_irq(&kc->job_lock);
+
+	blk_start_plug(&plug);
+	process_jobs(&kc->complete_jobs, kc, run_complete_job);
+	process_jobs(&kc->pages_jobs, kc, run_pages_job);
+	process_jobs(&kc->io_jobs, kc, run_io_job);
+	blk_finish_plug(&plug);
+}
+
+/*
+ * If we are copying a small region we just dispatch a single job
+ * to do the copy, otherwise the io has to be split up into many
+ * jobs.
+ */
+static void dispatch_job(struct kcopyd_job *job)
+{
+	struct dm_kcopyd_client *kc = job->kc;
+	atomic_inc(&kc->nr_jobs);
+	if (unlikely(!job->source.count))
+		push(&kc->callback_jobs, job);
+	else if (job->pages == &zero_page_list)
+		push(&kc->io_jobs, job);
+	else
+		push(&kc->pages_jobs, job);
+	wake(kc);
+}
+
+static void segment_complete(int read_err, unsigned long write_err,
+			     void *context)
+{
+	/* FIXME: tidy this function */
+	sector_t progress = 0;
+	sector_t count = 0;
+	struct kcopyd_job *sub_job = (struct kcopyd_job *) context;
+	struct kcopyd_job *job = sub_job->master_job;
+	struct dm_kcopyd_client *kc = job->kc;
+
+	mutex_lock(&job->lock);
+
+	/* update the error */
+	if (read_err)
+		job->read_err = 1;
+
+	if (write_err)
+		job->write_err |= write_err;
+
+	/*
+	 * Only dispatch more work if there hasn't been an error.
+	 */
+	if ((!job->read_err && !job->write_err) ||
+	    job->flags & BIT(DM_KCOPYD_IGNORE_ERROR)) {
+		/* get the next chunk of work */
+		progress = job->progress;
+		count = job->source.count - progress;
+		if (count) {
+			if (count > kc->sub_job_size)
+				count = kc->sub_job_size;
+
+			job->progress += count;
+		}
+	}
+	mutex_unlock(&job->lock);
+
+	if (count) {
+		int i;
+
+		*sub_job = *job;
+		sub_job->write_offset = progress;
+		sub_job->source.sector += progress;
+		sub_job->source.count = count;
+
+		for (i = 0; i < job->num_dests; i++) {
+			sub_job->dests[i].sector += progress;
+			sub_job->dests[i].count = count;
+		}
+
+		sub_job->fn = segment_complete;
+		sub_job->context = sub_job;
+		dispatch_job(sub_job);
+
+	} else if (atomic_dec_and_test(&job->sub_jobs)) {
+
+		/*
+		 * Queue the completion callback to the kcopyd thread.
+		 *
+		 * Some callers assume that all the completions are called
+		 * from a single thread and don't race with each other.
+		 *
+		 * We must not call the callback directly here because this
+		 * code may not be executing in the thread.
+		 */
+		push(&kc->complete_jobs, job);
+		wake(kc);
+	}
+}
+
+/*
+ * Create some sub jobs to share the work between them.
+ */
+static void split_job(struct kcopyd_job *master_job)
+{
+	int i;
+
+	atomic_inc(&master_job->kc->nr_jobs);
+
+	atomic_set(&master_job->sub_jobs, SPLIT_COUNT);
+	for (i = 0; i < SPLIT_COUNT; i++) {
+		master_job[i + 1].master_job = master_job;
+		segment_complete(0, 0u, &master_job[i + 1]);
+	}
+}
+
+void dm_kcopyd_copy(struct dm_kcopyd_client *kc, struct dm_io_region *from,
+		    unsigned int num_dests, struct dm_io_region *dests,
+		    unsigned int flags, dm_kcopyd_notify_fn fn, void *context)
+{
+	struct kcopyd_job *job;
+	int i;
+
+	/*
+	 * Allocate an array of jobs consisting of one master job
+	 * followed by SPLIT_COUNT sub jobs.
+	 */
+	job = mempool_alloc(&kc->job_pool, GFP_NOIO);
+	mutex_init(&job->lock);
+
+	/*
+	 * set up for the read.
+	 */
+	job->kc = kc;
+	job->flags = flags;
+	job->read_err = 0;
+	job->write_err = 0;
+
+	job->num_dests = num_dests;
+	memcpy(&job->dests, dests, sizeof(*dests) * num_dests);
+
+	/*
+	 * If one of the destination is a host-managed zoned block device,
+	 * we need to write sequentially. If one of the destination is a
+	 * host-aware device, then leave it to the caller to choose what to do.
+	 */
+	if (!(job->flags & BIT(DM_KCOPYD_WRITE_SEQ))) {
+		for (i = 0; i < job->num_dests; i++) {
+			if (bdev_zoned_model(dests[i].bdev) == BLK_ZONED_HM) {
+				job->flags |= BIT(DM_KCOPYD_WRITE_SEQ);
+				break;
+			}
+		}
+	}
+
+	/*
+	 * If we need to write sequentially, errors cannot be ignored.
+	 */
+	if (job->flags & BIT(DM_KCOPYD_WRITE_SEQ) &&
+	    job->flags & BIT(DM_KCOPYD_IGNORE_ERROR))
+		job->flags &= ~BIT(DM_KCOPYD_IGNORE_ERROR);
+
+	if (from) {
+		job->source = *from;
+		job->pages = NULL;
+		job->op = REQ_OP_READ;
+	} else {
+		memset(&job->source, 0, sizeof job->source);
+		job->source.count = job->dests[0].count;
+		job->pages = &zero_page_list;
+
+		/*
+		 * Use WRITE ZEROES to optimize zeroing if all dests support it.
+		 */
+		job->op = REQ_OP_WRITE_ZEROES;
+		for (i = 0; i < job->num_dests; i++)
+			if (!bdev_write_zeroes_sectors(job->dests[i].bdev)) {
+				job->op = REQ_OP_WRITE;
+				break;
+			}
+	}
+
+	job->fn = fn;
+	job->context = context;
+	job->master_job = job;
+	job->write_offset = 0;
+
+	if (job->source.count <= kc->sub_job_size)
+		dispatch_job(job);
+	else {
+		job->progress = 0;
+		split_job(job);
+	}
+}
+EXPORT_SYMBOL(dm_kcopyd_copy);
+
+void dm_kcopyd_zero(struct dm_kcopyd_client *kc,
+		    unsigned int num_dests, struct dm_io_region *dests,
+		    unsigned int flags, dm_kcopyd_notify_fn fn, void *context)
+{
+	dm_kcopyd_copy(kc, NULL, num_dests, dests, flags, fn, context);
+}
+EXPORT_SYMBOL(dm_kcopyd_zero);
+
+void *dm_kcopyd_prepare_callback(struct dm_kcopyd_client *kc,
+				 dm_kcopyd_notify_fn fn, void *context)
+{
+	struct kcopyd_job *job;
+
+	job = mempool_alloc(&kc->job_pool, GFP_NOIO);
+
+	memset(job, 0, sizeof(struct kcopyd_job));
+	job->kc = kc;
+	job->fn = fn;
+	job->context = context;
+	job->master_job = job;
+
+	atomic_inc(&kc->nr_jobs);
+
+	return job;
+}
+EXPORT_SYMBOL(dm_kcopyd_prepare_callback);
+
+void dm_kcopyd_do_callback(void *j, int read_err, unsigned long write_err)
+{
+	struct kcopyd_job *job = j;
+	struct dm_kcopyd_client *kc = job->kc;
+
+	job->read_err = read_err;
+	job->write_err = write_err;
+
+	push(&kc->callback_jobs, job);
+	wake(kc);
+}
+EXPORT_SYMBOL(dm_kcopyd_do_callback);
+
+/*
+ * Cancels a kcopyd job, eg. someone might be deactivating a
+ * mirror.
+ */
+#if 0
+int kcopyd_cancel(struct kcopyd_job *job, int block)
+{
+	/* FIXME: finish */
+	return -1;
+}
+#endif  /*  0  */
+
+/*-----------------------------------------------------------------
+ * Client setup
+ *---------------------------------------------------------------*/
+struct dm_kcopyd_client *dm_kcopyd_client_create(struct dm_kcopyd_throttle *throttle)
+{
+	int r;
+	unsigned int reserve_pages;
+	struct dm_kcopyd_client *kc;
+
+	kc = kzalloc(sizeof(*kc), GFP_KERNEL);
+	if (!kc)
+		return ERR_PTR(-ENOMEM);
+
+	spin_lock_init(&kc->job_lock);
+	INIT_LIST_HEAD(&kc->callback_jobs);
+	INIT_LIST_HEAD(&kc->complete_jobs);
+	INIT_LIST_HEAD(&kc->io_jobs);
+	INIT_LIST_HEAD(&kc->pages_jobs);
+	kc->throttle = throttle;
+
+	r = mempool_init_slab_pool(&kc->job_pool, MIN_JOBS, _job_cache);
+	if (r)
+		goto bad_slab;
+
+	INIT_WORK(&kc->kcopyd_work, do_work);
+	kc->kcopyd_wq = alloc_workqueue("kcopyd", WQ_MEM_RECLAIM, 0);
+	if (!kc->kcopyd_wq) {
+		r = -ENOMEM;
+		goto bad_workqueue;
+	}
+
+	kc->sub_job_size = dm_get_kcopyd_subjob_size();
+	reserve_pages = DIV_ROUND_UP(kc->sub_job_size << SECTOR_SHIFT, PAGE_SIZE);
+
+	kc->pages = NULL;
+	kc->nr_reserved_pages = kc->nr_free_pages = 0;
+	r = client_reserve_pages(kc, reserve_pages);
+	if (r)
+		goto bad_client_pages;
+
+	kc->io_client = dm_io_client_create();
+	if (IS_ERR(kc->io_client)) {
+		r = PTR_ERR(kc->io_client);
+		goto bad_io_client;
+	}
+
+	init_waitqueue_head(&kc->destroyq);
+	atomic_set(&kc->nr_jobs, 0);
+
+	return kc;
+
+bad_io_client:
+	client_free_pages(kc);
+bad_client_pages:
+	destroy_workqueue(kc->kcopyd_wq);
+bad_workqueue:
+	mempool_exit(&kc->job_pool);
+bad_slab:
+	kfree(kc);
+
+	return ERR_PTR(r);
+}
+EXPORT_SYMBOL(dm_kcopyd_client_create);
+
+void dm_kcopyd_client_destroy(struct dm_kcopyd_client *kc)
+{
+	/* Wait for completion of all jobs submitted by this client. */
+	wait_event(kc->destroyq, !atomic_read(&kc->nr_jobs));
+
+	BUG_ON(!list_empty(&kc->callback_jobs));
+	BUG_ON(!list_empty(&kc->complete_jobs));
+	BUG_ON(!list_empty(&kc->io_jobs));
+	BUG_ON(!list_empty(&kc->pages_jobs));
+	destroy_workqueue(kc->kcopyd_wq);
+	dm_io_client_destroy(kc->io_client);
+	client_free_pages(kc);
+	mempool_exit(&kc->job_pool);
+	kfree(kc);
+}
+EXPORT_SYMBOL(dm_kcopyd_client_destroy);
+
+void dm_kcopyd_client_flush(struct dm_kcopyd_client *kc)
+{
+	flush_workqueue(kc->kcopyd_wq);
+}
+EXPORT_SYMBOL(dm_kcopyd_client_flush);