reciprocal_divide: update/correction of the algorithm

[mirror_ubuntu-artful-kernel.git] / drivers / md / dm-region-hash.c

/*
 * Copyright (C) 2003 Sistina Software Limited.
 * Copyright (C) 2004-2008 Red Hat, Inc. All rights reserved.
 *
 * This file is released under the GPL.
 */

#include <linux/dm-dirty-log.h>
#include <linux/dm-region-hash.h>

#include <linux/ctype.h>
#include <linux/init.h>
#include <linux/module.h>
#include <linux/slab.h>
#include <linux/vmalloc.h>

#include "dm.h"

#define DM_MSG_PREFIX   "region hash"

/*-----------------------------------------------------------------
 * Region hash
 *
 * The mirror splits itself up into discrete regions.  Each
 * region can be in one of three states: clean, dirty,
 * nosync.  There is no need to put clean regions in the hash.
 *
 * In addition to being present in the hash table a region _may_
 * be present on one of three lists.
 *
 *   clean_regions: Regions on this list have no io pending to
 *   them, they are in sync, we are no longer interested in them,
 *   they are dull.  dm_rh_update_states() will remove them from the
 *   hash table.
 *
 *   quiesced_regions: These regions have been spun down, ready
 *   for recovery.  rh_recovery_start() will remove regions from
 *   this list and hand them to kmirrord, which will schedule the
 *   recovery io with kcopyd.
 *
 *   recovered_regions: Regions that kcopyd has successfully
 *   recovered.  dm_rh_update_states() will now schedule any delayed
 *   io, up the recovery_count, and remove the region from the
 *   hash.
 *
 * There are 2 locks:
 *   A rw spin lock 'hash_lock' protects just the hash table,
 *   this is never held in write mode from interrupt context,
 *   which I believe means that we only have to disable irqs when
 *   doing a write lock.
 *
 *   An ordinary spin lock 'region_lock' that protects the three
 *   lists in the region_hash, with the 'state', 'list' and
 *   'delayed_bios' fields of the regions.  This is used from irq
 *   context, so all other uses will have to suspend local irqs.
 *---------------------------------------------------------------*/
struct dm_region_hash {
        uint32_t region_size;
        unsigned region_shift;

        /* holds persistent region state */
        struct dm_dirty_log *log;

        /* hash table */
        rwlock_t hash_lock;
        mempool_t *region_pool;
        unsigned mask;
        unsigned nr_buckets;
        unsigned prime;
        unsigned shift;
        struct list_head *buckets;

        unsigned max_recovery; /* Max # of regions to recover in parallel */

        spinlock_t region_lock;
        atomic_t recovery_in_flight;
        struct semaphore recovery_count;
        struct list_head clean_regions;
        struct list_head quiesced_regions;
        struct list_head recovered_regions;
        struct list_head failed_recovered_regions;

        /*
         * If there was a flush failure no regions can be marked clean.
         */
        int flush_failure;

        void *context;
        sector_t target_begin;

        /* Callback function to schedule bios writes */
        void (*dispatch_bios)(void *context, struct bio_list *bios);

        /* Callback function to wakeup callers worker thread. */
        void (*wakeup_workers)(void *context);

        /* Callback function to wakeup callers recovery waiters. */
        void (*wakeup_all_recovery_waiters)(void *context);
};

struct dm_region {
        struct dm_region_hash *rh;      /* FIXME: can we get rid of this ? */
        region_t key;
        int state;

        struct list_head hash_list;
        struct list_head list;

        atomic_t pending;
        struct bio_list delayed_bios;
};

/*
 * Conversion fns
 */
static region_t dm_rh_sector_to_region(struct dm_region_hash *rh, sector_t sector)
{
        return sector >> rh->region_shift;
}

sector_t dm_rh_region_to_sector(struct dm_region_hash *rh, region_t region)
{
        return region << rh->region_shift;
}
EXPORT_SYMBOL_GPL(dm_rh_region_to_sector);

region_t dm_rh_bio_to_region(struct dm_region_hash *rh, struct bio *bio)
{
        return dm_rh_sector_to_region(rh, bio->bi_sector - rh->target_begin);
}
EXPORT_SYMBOL_GPL(dm_rh_bio_to_region);

void *dm_rh_region_context(struct dm_region *reg)
{
        return reg->rh->context;
}
EXPORT_SYMBOL_GPL(dm_rh_region_context);

region_t dm_rh_get_region_key(struct dm_region *reg)
{
        return reg->key;
}
EXPORT_SYMBOL_GPL(dm_rh_get_region_key);

sector_t dm_rh_get_region_size(struct dm_region_hash *rh)
{
        return rh->region_size;
}
EXPORT_SYMBOL_GPL(dm_rh_get_region_size);

/*
 * FIXME: shall we pass in a structure instead of all these args to
 * dm_region_hash_create()????
 */
#define RH_HASH_MULT 2654435387U
#define RH_HASH_SHIFT 12

#define MIN_REGIONS 64
struct dm_region_hash *dm_region_hash_create(
                void *context, void (*dispatch_bios)(void *context,
                                                     struct bio_list *bios),
                void (*wakeup_workers)(void *context),
                void (*wakeup_all_recovery_waiters)(void *context),
                sector_t target_begin, unsigned max_recovery,
                struct dm_dirty_log *log, uint32_t region_size,
                region_t nr_regions)
{
        struct dm_region_hash *rh;
        unsigned nr_buckets, max_buckets;
        size_t i;

        /*
         * Calculate a suitable number of buckets for our hash
         * table.
         */
        max_buckets = nr_regions >> 6;
        for (nr_buckets = 128u; nr_buckets < max_buckets; nr_buckets <<= 1)
                ;
        nr_buckets >>= 1;

        rh = kmalloc(sizeof(*rh), GFP_KERNEL);
        if (!rh) {
                DMERR("unable to allocate region hash memory");
                return ERR_PTR(-ENOMEM);
        }

        rh->context = context;
        rh->dispatch_bios = dispatch_bios;
        rh->wakeup_workers = wakeup_workers;
        rh->wakeup_all_recovery_waiters = wakeup_all_recovery_waiters;
        rh->target_begin = target_begin;
        rh->max_recovery = max_recovery;
        rh->log = log;
        rh->region_size = region_size;
        rh->region_shift = ffs(region_size) - 1;
        rwlock_init(&rh->hash_lock);
        rh->mask = nr_buckets - 1;
        rh->nr_buckets = nr_buckets;

        rh->shift = RH_HASH_SHIFT;
        rh->prime = RH_HASH_MULT;

        rh->buckets = vmalloc(nr_buckets * sizeof(*rh->buckets));
        if (!rh->buckets) {
                DMERR("unable to allocate region hash bucket memory");
                kfree(rh);
                return ERR_PTR(-ENOMEM);
        }

        for (i = 0; i < nr_buckets; i++)
                INIT_LIST_HEAD(rh->buckets + i);

        spin_lock_init(&rh->region_lock);
        sema_init(&rh->recovery_count, 0);
        atomic_set(&rh->recovery_in_flight, 0);
        INIT_LIST_HEAD(&rh->clean_regions);
        INIT_LIST_HEAD(&rh->quiesced_regions);
        INIT_LIST_HEAD(&rh->recovered_regions);
        INIT_LIST_HEAD(&rh->failed_recovered_regions);
        rh->flush_failure = 0;

        rh->region_pool = mempool_create_kmalloc_pool(MIN_REGIONS,
                                                      sizeof(struct dm_region));
        if (!rh->region_pool) {
                vfree(rh->buckets);
                kfree(rh);
                rh = ERR_PTR(-ENOMEM);
        }

        return rh;
}
EXPORT_SYMBOL_GPL(dm_region_hash_create);

void dm_region_hash_destroy(struct dm_region_hash *rh)
{
        unsigned h;
        struct dm_region *reg, *nreg;

        BUG_ON(!list_empty(&rh->quiesced_regions));
        for (h = 0; h < rh->nr_buckets; h++) {
                list_for_each_entry_safe(reg, nreg, rh->buckets + h,
                                         hash_list) {
                        BUG_ON(atomic_read(&reg->pending));
                        mempool_free(reg, rh->region_pool);
                }
        }

        if (rh->log)
                dm_dirty_log_destroy(rh->log);

        if (rh->region_pool)
                mempool_destroy(rh->region_pool);

        vfree(rh->buckets);
        kfree(rh);
}
EXPORT_SYMBOL_GPL(dm_region_hash_destroy);

struct dm_dirty_log *dm_rh_dirty_log(struct dm_region_hash *rh)
{
        return rh->log;
}
EXPORT_SYMBOL_GPL(dm_rh_dirty_log);

static unsigned rh_hash(struct dm_region_hash *rh, region_t region)
{
        return (unsigned) ((region * rh->prime) >> rh->shift) & rh->mask;
}

static struct dm_region *__rh_lookup(struct dm_region_hash *rh, region_t region)
{
        struct dm_region *reg;
        struct list_head *bucket = rh->buckets + rh_hash(rh, region);

        list_for_each_entry(reg, bucket, hash_list)
                if (reg->key == region)
                        return reg;

        return NULL;
}

static void __rh_insert(struct dm_region_hash *rh, struct dm_region *reg)
{
        list_add(&reg->hash_list, rh->buckets + rh_hash(rh, reg->key));
}

static struct dm_region *__rh_alloc(struct dm_region_hash *rh, region_t region)
{
        struct dm_region *reg, *nreg;

        nreg = mempool_alloc(rh->region_pool, GFP_ATOMIC);
        if (unlikely(!nreg))
                nreg = kmalloc(sizeof(*nreg), GFP_NOIO | __GFP_NOFAIL);

        nreg->state = rh->log->type->in_sync(rh->log, region, 1) ?
                      DM_RH_CLEAN : DM_RH_NOSYNC;
        nreg->rh = rh;
        nreg->key = region;
        INIT_LIST_HEAD(&nreg->list);
        atomic_set(&nreg->pending, 0);
        bio_list_init(&nreg->delayed_bios);

        write_lock_irq(&rh->hash_lock);
        reg = __rh_lookup(rh, region);
        if (reg)
                /* We lost the race. */
                mempool_free(nreg, rh->region_pool);
        else {
                __rh_insert(rh, nreg);
                if (nreg->state == DM_RH_CLEAN) {
                        spin_lock(&rh->region_lock);
                        list_add(&nreg->list, &rh->clean_regions);
                        spin_unlock(&rh->region_lock);
                }

                reg = nreg;
        }
        write_unlock_irq(&rh->hash_lock);

        return reg;
}

static struct dm_region *__rh_find(struct dm_region_hash *rh, region_t region)
{
        struct dm_region *reg;

        reg = __rh_lookup(rh, region);
        if (!reg) {
                read_unlock(&rh->hash_lock);
                reg = __rh_alloc(rh, region);
                read_lock(&rh->hash_lock);
        }

        return reg;
}

int dm_rh_get_state(struct dm_region_hash *rh, region_t region, int may_block)
{
        int r;
        struct dm_region *reg;

        read_lock(&rh->hash_lock);
        reg = __rh_lookup(rh, region);
        read_unlock(&rh->hash_lock);

        if (reg)
                return reg->state;

        /*
         * The region wasn't in the hash, so we fall back to the
         * dirty log.
         */
        r = rh->log->type->in_sync(rh->log, region, may_block);

        /*
         * Any error from the dirty log (eg. -EWOULDBLOCK) gets
         * taken as a DM_RH_NOSYNC
         */
        return r == 1 ? DM_RH_CLEAN : DM_RH_NOSYNC;
}
EXPORT_SYMBOL_GPL(dm_rh_get_state);

static void complete_resync_work(struct dm_region *reg, int success)
{
        struct dm_region_hash *rh = reg->rh;

        rh->log->type->set_region_sync(rh->log, reg->key, success);

        /*
         * Dispatch the bios before we call 'wake_up_all'.
         * This is important because if we are suspending,
         * we want to know that recovery is complete and
         * the work queue is flushed.  If we wake_up_all
         * before we dispatch_bios (queue bios and call wake()),
         * then we risk suspending before the work queue
         * has been properly flushed.
         */
        rh->dispatch_bios(rh->context, &reg->delayed_bios);
        if (atomic_dec_and_test(&rh->recovery_in_flight))
                rh->wakeup_all_recovery_waiters(rh->context);
        up(&rh->recovery_count);
}

/* dm_rh_mark_nosync
 * @ms
 * @bio
 *
 * The bio was written on some mirror(s) but failed on other mirror(s).
 * We can successfully endio the bio but should avoid the region being
 * marked clean by setting the state DM_RH_NOSYNC.
 *
 * This function is _not_ safe in interrupt context!
 */
void dm_rh_mark_nosync(struct dm_region_hash *rh, struct bio *bio)
{
        unsigned long flags;
        struct dm_dirty_log *log = rh->log;
        struct dm_region *reg;
        region_t region = dm_rh_bio_to_region(rh, bio);
        int recovering = 0;

        if (bio->bi_rw & REQ_FLUSH) {
                rh->flush_failure = 1;
                return;
        }

        if (bio->bi_rw & REQ_DISCARD)
                return;

        /* We must inform the log that the sync count has changed. */
        log->type->set_region_sync(log, region, 0);

        read_lock(&rh->hash_lock);
        reg = __rh_find(rh, region);
        read_unlock(&rh->hash_lock);

        /* region hash entry should exist because write was in-flight */
        BUG_ON(!reg);
        BUG_ON(!list_empty(&reg->list));

        spin_lock_irqsave(&rh->region_lock, flags);
        /*
         * Possible cases:
         *   1) DM_RH_DIRTY
         *   2) DM_RH_NOSYNC: was dirty, other preceding writes failed
         *   3) DM_RH_RECOVERING: flushing pending writes
         * Either case, the region should have not been connected to list.
         */
        recovering = (reg->state == DM_RH_RECOVERING);
        reg->state = DM_RH_NOSYNC;
        BUG_ON(!list_empty(&reg->list));
        spin_unlock_irqrestore(&rh->region_lock, flags);

        if (recovering)
                complete_resync_work(reg, 0);
}
EXPORT_SYMBOL_GPL(dm_rh_mark_nosync);

void dm_rh_update_states(struct dm_region_hash *rh, int errors_handled)
{
        struct dm_region *reg, *next;

        LIST_HEAD(clean);
        LIST_HEAD(recovered);
        LIST_HEAD(failed_recovered);

        /*
         * Quickly grab the lists.
         */
        write_lock_irq(&rh->hash_lock);
        spin_lock(&rh->region_lock);
        if (!list_empty(&rh->clean_regions)) {
                list_splice_init(&rh->clean_regions, &clean);

                list_for_each_entry(reg, &clean, list)
                        list_del(&reg->hash_list);
        }

        if (!list_empty(&rh->recovered_regions)) {
                list_splice_init(&rh->recovered_regions, &recovered);

                list_for_each_entry(reg, &recovered, list)
                        list_del(&reg->hash_list);
        }

        if (!list_empty(&rh->failed_recovered_regions)) {
                list_splice_init(&rh->failed_recovered_regions,
                                 &failed_recovered);

                list_for_each_entry(reg, &failed_recovered, list)
                        list_del(&reg->hash_list);
        }

        spin_unlock(&rh->region_lock);
        write_unlock_irq(&rh->hash_lock);

        /*
         * All the regions on the recovered and clean lists have
         * now been pulled out of the system, so no need to do
         * any more locking.
         */
        list_for_each_entry_safe(reg, next, &recovered, list) {
                rh->log->type->clear_region(rh->log, reg->key);
                complete_resync_work(reg, 1);
                mempool_free(reg, rh->region_pool);
        }

        list_for_each_entry_safe(reg, next, &failed_recovered, list) {
                complete_resync_work(reg, errors_handled ? 0 : 1);
                mempool_free(reg, rh->region_pool);
        }

        list_for_each_entry_safe(reg, next, &clean, list) {
                rh->log->type->clear_region(rh->log, reg->key);
                mempool_free(reg, rh->region_pool);
        }

        rh->log->type->flush(rh->log);
}
EXPORT_SYMBOL_GPL(dm_rh_update_states);

static void rh_inc(struct dm_region_hash *rh, region_t region)
{
        struct dm_region *reg;

        read_lock(&rh->hash_lock);
        reg = __rh_find(rh, region);

        spin_lock_irq(&rh->region_lock);
        atomic_inc(&reg->pending);

        if (reg->state == DM_RH_CLEAN) {
                reg->state = DM_RH_DIRTY;
                list_del_init(&reg->list);      /* take off the clean list */
                spin_unlock_irq(&rh->region_lock);

                rh->log->type->mark_region(rh->log, reg->key);
        } else
                spin_unlock_irq(&rh->region_lock);


        read_unlock(&rh->hash_lock);
}

void dm_rh_inc_pending(struct dm_region_hash *rh, struct bio_list *bios)
{
        struct bio *bio;

        for (bio = bios->head; bio; bio = bio->bi_next) {
                if (bio->bi_rw & (REQ_FLUSH | REQ_DISCARD))
                        continue;
                rh_inc(rh, dm_rh_bio_to_region(rh, bio));
        }
}
EXPORT_SYMBOL_GPL(dm_rh_inc_pending);

void dm_rh_dec(struct dm_region_hash *rh, region_t region)
{
        unsigned long flags;
        struct dm_region *reg;
        int should_wake = 0;

        read_lock(&rh->hash_lock);
        reg = __rh_lookup(rh, region);
        read_unlock(&rh->hash_lock);

        spin_lock_irqsave(&rh->region_lock, flags);
        if (atomic_dec_and_test(&reg->pending)) {
                /*
                 * There is no pending I/O for this region.
                 * We can move the region to corresponding list for next action.
                 * At this point, the region is not yet connected to any list.
                 *
                 * If the state is DM_RH_NOSYNC, the region should be kept off
                 * from clean list.
                 * The hash entry for DM_RH_NOSYNC will remain in memory
                 * until the region is recovered or the map is reloaded.
                 */

                /* do nothing for DM_RH_NOSYNC */
                if (unlikely(rh->flush_failure)) {
                        /*
                         * If a write flush failed some time ago, we
                         * don't know whether or not this write made it
                         * to the disk, so we must resync the device.
                         */
                        reg->state = DM_RH_NOSYNC;
                } else if (reg->state == DM_RH_RECOVERING) {
                        list_add_tail(&reg->list, &rh->quiesced_regions);
                } else if (reg->state == DM_RH_DIRTY) {
                        reg->state = DM_RH_CLEAN;
                        list_add(&reg->list, &rh->clean_regions);
                }
                should_wake = 1;
        }
        spin_unlock_irqrestore(&rh->region_lock, flags);

        if (should_wake)
                rh->wakeup_workers(rh->context);
}
EXPORT_SYMBOL_GPL(dm_rh_dec);

/*
 * Starts quiescing a region in preparation for recovery.
 */
static int __rh_recovery_prepare(struct dm_region_hash *rh)
{
        int r;
        region_t region;
        struct dm_region *reg;

        /*
         * Ask the dirty log what's next.
         */
        r = rh->log->type->get_resync_work(rh->log, &region);
        if (r <= 0)
                return r;

        /*
         * Get this region, and start it quiescing by setting the
         * recovering flag.
         */
        read_lock(&rh->hash_lock);
        reg = __rh_find(rh, region);
        read_unlock(&rh->hash_lock);

        spin_lock_irq(&rh->region_lock);
        reg->state = DM_RH_RECOVERING;

        /* Already quiesced ? */
        if (atomic_read(&reg->pending))
                list_del_init(&reg->list);
        else
                list_move(&reg->list, &rh->quiesced_regions);

        spin_unlock_irq(&rh->region_lock);

        return 1;
}

void dm_rh_recovery_prepare(struct dm_region_hash *rh)
{
        /* Extra reference to avoid race with dm_rh_stop_recovery */
        atomic_inc(&rh->recovery_in_flight);

        while (!down_trylock(&rh->recovery_count)) {
                atomic_inc(&rh->recovery_in_flight);
                if (__rh_recovery_prepare(rh) <= 0) {
                        atomic_dec(&rh->recovery_in_flight);
                        up(&rh->recovery_count);
                        break;
                }
        }

        /* Drop the extra reference */
        if (atomic_dec_and_test(&rh->recovery_in_flight))
                rh->wakeup_all_recovery_waiters(rh->context);
}
EXPORT_SYMBOL_GPL(dm_rh_recovery_prepare);

/*
 * Returns any quiesced regions.
 */
struct dm_region *dm_rh_recovery_start(struct dm_region_hash *rh)
{
        struct dm_region *reg = NULL;

        spin_lock_irq(&rh->region_lock);
        if (!list_empty(&rh->quiesced_regions)) {
                reg = list_entry(rh->quiesced_regions.next,
                                 struct dm_region, list);
                list_del_init(&reg->list);  /* remove from the quiesced list */
        }
        spin_unlock_irq(&rh->region_lock);

        return reg;
}
EXPORT_SYMBOL_GPL(dm_rh_recovery_start);

void dm_rh_recovery_end(struct dm_region *reg, int success)
{
        struct dm_region_hash *rh = reg->rh;

        spin_lock_irq(&rh->region_lock);
        if (success)
                list_add(&reg->list, &reg->rh->recovered_regions);
        else
                list_add(&reg->list, &reg->rh->failed_recovered_regions);

        spin_unlock_irq(&rh->region_lock);

        rh->wakeup_workers(rh->context);
}
EXPORT_SYMBOL_GPL(dm_rh_recovery_end);

/* Return recovery in flight count. */
int dm_rh_recovery_in_flight(struct dm_region_hash *rh)
{
        return atomic_read(&rh->recovery_in_flight);
}
EXPORT_SYMBOL_GPL(dm_rh_recovery_in_flight);

int dm_rh_flush(struct dm_region_hash *rh)
{
        return rh->log->type->flush(rh->log);
}
EXPORT_SYMBOL_GPL(dm_rh_flush);

void dm_rh_delay(struct dm_region_hash *rh, struct bio *bio)
{
        struct dm_region *reg;

        read_lock(&rh->hash_lock);
        reg = __rh_find(rh, dm_rh_bio_to_region(rh, bio));
        bio_list_add(&reg->delayed_bios, bio);
        read_unlock(&rh->hash_lock);
}
EXPORT_SYMBOL_GPL(dm_rh_delay);

void dm_rh_stop_recovery(struct dm_region_hash *rh)
{
        int i;

        /* wait for any recovering regions */
        for (i = 0; i < rh->max_recovery; i++)
                down(&rh->recovery_count);
}
EXPORT_SYMBOL_GPL(dm_rh_stop_recovery);

void dm_rh_start_recovery(struct dm_region_hash *rh)
{
        int i;

        for (i = 0; i < rh->max_recovery; i++)
                up(&rh->recovery_count);

        rh->wakeup_workers(rh->context);
}
EXPORT_SYMBOL_GPL(dm_rh_start_recovery);

MODULE_DESCRIPTION(DM_NAME " region hash");
MODULE_AUTHOR("Joe Thornber/Heinz Mauelshagen <dm-devel@redhat.com>");
MODULE_LICENSE("GPL");