dm-bio-prison.c

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/*
 * Copyright (C) 2012 Red Hat, Inc.
 *
 * This file is released under the GPL.
 */

#include "dm.h"
#include "dm-bio-prison.h"

#include <linux/spinlock.h>
#include <linux/mempool.h>
#include <linux/module.h>
#include <linux/slab.h>

/*----------------------------------------------------------------*/

struct dm_bio_prison_cell {
    struct hlist_node list;
    struct dm_bio_prison *prison;
    struct dm_cell_key key;
    struct bio *holder;
    struct bio_list bios;
};

struct dm_bio_prison {
    spinlock_t lock;
    mempool_t *cell_pool;

    unsigned nr_buckets;
    unsigned hash_mask;
    struct hlist_head *cells;
};

/*----------------------------------------------------------------*/

static uint32_t calc_nr_buckets(unsigned nr_cells)
{
    uint32_t n = 128;

    nr_cells /= 4;
    nr_cells = min(nr_cells, 8192u);

    while (n < nr_cells)
        n <<= 1;

    return n;
}

static struct kmem_cache *_cell_cache;

/*
 * @nr_cells should be the number of cells you want in use _concurrently_.
 * Don't confuse it with the number of distinct keys.
 */
struct dm_bio_prison *dm_bio_prison_create(unsigned nr_cells)
{
    unsigned i;
    uint32_t nr_buckets = calc_nr_buckets(nr_cells);
    size_t len = sizeof(struct dm_bio_prison) +
        (sizeof(struct hlist_head) * nr_buckets);
    struct dm_bio_prison *prison = kmalloc(len, GFP_KERNEL);

    if (!prison)
        return NULL;

    spin_lock_init(&prison->lock);
    prison->cell_pool = mempool_create_slab_pool(nr_cells, _cell_cache);
    if (!prison->cell_pool) {
        kfree(prison);
        return NULL;
    }

    prison->nr_buckets = nr_buckets;
    prison->hash_mask = nr_buckets - 1;
    prison->cells = (struct hlist_head *) (prison + 1);
    for (i = 0; i < nr_buckets; i++)
        INIT_HLIST_HEAD(prison->cells + i);

    return prison;
}
EXPORT_SYMBOL_GPL(dm_bio_prison_create);

void dm_bio_prison_destroy(struct dm_bio_prison *prison)
{
    mempool_destroy(prison->cell_pool);
    kfree(prison);
}
EXPORT_SYMBOL_GPL(dm_bio_prison_destroy);

static uint32_t hash_key(struct dm_bio_prison *prison, struct dm_cell_key *key)
{
    const unsigned long BIG_PRIME = 4294967291UL;
    uint64_t hash = key->block * BIG_PRIME;

    return (uint32_t) (hash & prison->hash_mask);
}

static int keys_equal(struct dm_cell_key *lhs, struct dm_cell_key *rhs)
{
           return (lhs->virtual == rhs->virtual) &&
               (lhs->dev == rhs->dev) &&
               (lhs->block == rhs->block);
}

static struct dm_bio_prison_cell *__search_bucket(struct hlist_head *bucket,
                          struct dm_cell_key *key)
{
    struct dm_bio_prison_cell *cell;
    struct hlist_node *tmp;

    hlist_for_each_entry(cell, tmp, bucket, list)
        if (keys_equal(&cell->key, key))
            return cell;

    return NULL;
}

/*
 * This may block if a new cell needs allocating.  You must ensure that
 * cells will be unlocked even if the calling thread is blocked.
 *
 * Returns 1 if the cell was already held, 0 if @inmate is the new holder.
 */
int dm_bio_detain(struct dm_bio_prison *prison, struct dm_cell_key *key,
          struct bio *inmate, struct dm_bio_prison_cell **ref)
{
    int r = 1;
    unsigned long flags;
    uint32_t hash = hash_key(prison, key);
    struct dm_bio_prison_cell *cell, *cell2;

    BUG_ON(hash > prison->nr_buckets);

    spin_lock_irqsave(&prison->lock, flags);

    cell = __search_bucket(prison->cells + hash, key);
    if (cell) {
        bio_list_add(&cell->bios, inmate);
        goto out;
    }

    /*
     * Allocate a new cell
     */
    spin_unlock_irqrestore(&prison->lock, flags);
    cell2 = mempool_alloc(prison->cell_pool, GFP_NOIO);
    spin_lock_irqsave(&prison->lock, flags);

    /*
     * We've been unlocked, so we have to double check that
     * nobody else has inserted this cell in the meantime.
     */
    cell = __search_bucket(prison->cells + hash, key);
    if (cell) {
        mempool_free(cell2, prison->cell_pool);
        bio_list_add(&cell->bios, inmate);
        goto out;
    }

    /*
     * Use new cell.
     */
    cell = cell2;

    cell->prison = prison;
    memcpy(&cell->key, key, sizeof(cell->key));
    cell->holder = inmate;
    bio_list_init(&cell->bios);
    hlist_add_head(&cell->list, prison->cells + hash);

    r = 0;

out:
    spin_unlock_irqrestore(&prison->lock, flags);

    *ref = cell;

    return r;
}
EXPORT_SYMBOL_GPL(dm_bio_detain);

/*
 * @inmates must have been initialised prior to this call
 */
static void __cell_release(struct dm_bio_prison_cell *cell, struct bio_list *inmates)
{
    struct dm_bio_prison *prison = cell->prison;

    hlist_del(&cell->list);

    if (inmates) {
        bio_list_add(inmates, cell->holder);
        bio_list_merge(inmates, &cell->bios);
    }

    mempool_free(cell, prison->cell_pool);
}

void dm_cell_release(struct dm_bio_prison_cell *cell, struct bio_list *bios)
{
    unsigned long flags;
    struct dm_bio_prison *prison = cell->prison;

    spin_lock_irqsave(&prison->lock, flags);
    __cell_release(cell, bios);
    spin_unlock_irqrestore(&prison->lock, flags);
}
EXPORT_SYMBOL_GPL(dm_cell_release);

/*
 * There are a couple of places where we put a bio into a cell briefly
 * before taking it out again.  In these situations we know that no other
 * bio may be in the cell.  This function releases the cell, and also does
 * a sanity check.
 */
static void __cell_release_singleton(struct dm_bio_prison_cell *cell, struct bio *bio)
{
    BUG_ON(cell->holder != bio);
    BUG_ON(!bio_list_empty(&cell->bios));

    __cell_release(cell, NULL);
}

void dm_cell_release_singleton(struct dm_bio_prison_cell *cell, struct bio *bio)
{
    unsigned long flags;
    struct dm_bio_prison *prison = cell->prison;

    spin_lock_irqsave(&prison->lock, flags);
    __cell_release_singleton(cell, bio);
    spin_unlock_irqrestore(&prison->lock, flags);
}
EXPORT_SYMBOL_GPL(dm_cell_release_singleton);

/*
 * Sometimes we don't want the holder, just the additional bios.
 */
static void __cell_release_no_holder(struct dm_bio_prison_cell *cell, struct bio_list *inmates)
{
    struct dm_bio_prison *prison = cell->prison;

    hlist_del(&cell->list);
    bio_list_merge(inmates, &cell->bios);

    mempool_free(cell, prison->cell_pool);
}

void dm_cell_release_no_holder(struct dm_bio_prison_cell *cell, struct bio_list *inmates)
{
    unsigned long flags;
    struct dm_bio_prison *prison = cell->prison;

    spin_lock_irqsave(&prison->lock, flags);
    __cell_release_no_holder(cell, inmates);
    spin_unlock_irqrestore(&prison->lock, flags);
}
EXPORT_SYMBOL_GPL(dm_cell_release_no_holder);

void dm_cell_error(struct dm_bio_prison_cell *cell)
{
    struct dm_bio_prison *prison = cell->prison;
    struct bio_list bios;
    struct bio *bio;
    unsigned long flags;

    bio_list_init(&bios);

    spin_lock_irqsave(&prison->lock, flags);
    __cell_release(cell, &bios);
    spin_unlock_irqrestore(&prison->lock, flags);

    while ((bio = bio_list_pop(&bios)))
        bio_io_error(bio);
}
EXPORT_SYMBOL_GPL(dm_cell_error);

/*----------------------------------------------------------------*/

#define DEFERRED_SET_SIZE 64

struct dm_deferred_entry {
    struct dm_deferred_set *ds;
    unsigned count;
    struct list_head work_items;
};

struct dm_deferred_set {
    spinlock_t lock;
    unsigned current_entry;
    unsigned sweeper;
    struct dm_deferred_entry entries[DEFERRED_SET_SIZE];
};

struct dm_deferred_set *dm_deferred_set_create(void)
{
    int i;
    struct dm_deferred_set *ds;

    ds = kmalloc(sizeof(*ds), GFP_KERNEL);
    if (!ds)
        return NULL;

    spin_lock_init(&ds->lock);
    ds->current_entry = 0;
    ds->sweeper = 0;
    for (i = 0; i < DEFERRED_SET_SIZE; i++) {
        ds->entries[i].ds = ds;
        ds->entries[i].count = 0;
        INIT_LIST_HEAD(&ds->entries[i].work_items);
    }

    return ds;
}
EXPORT_SYMBOL_GPL(dm_deferred_set_create);

void dm_deferred_set_destroy(struct dm_deferred_set *ds)
{
    kfree(ds);
}
EXPORT_SYMBOL_GPL(dm_deferred_set_destroy);

struct dm_deferred_entry *dm_deferred_entry_inc(struct dm_deferred_set *ds)
{
    unsigned long flags;
    struct dm_deferred_entry *entry;

    spin_lock_irqsave(&ds->lock, flags);
    entry = ds->entries + ds->current_entry;
    entry->count++;
    spin_unlock_irqrestore(&ds->lock, flags);

    return entry;
}
EXPORT_SYMBOL_GPL(dm_deferred_entry_inc);

static unsigned ds_next(unsigned index)
{
    return (index + 1) % DEFERRED_SET_SIZE;
}

static void __sweep(struct dm_deferred_set *ds, struct list_head *head)
{
    while ((ds->sweeper != ds->current_entry) &&
           !ds->entries[ds->sweeper].count) {
        list_splice_init(&ds->entries[ds->sweeper].work_items, head);
        ds->sweeper = ds_next(ds->sweeper);
    }

    if ((ds->sweeper == ds->current_entry) && !ds->entries[ds->sweeper].count)
        list_splice_init(&ds->entries[ds->sweeper].work_items, head);
}

void dm_deferred_entry_dec(struct dm_deferred_entry *entry, struct list_head *head)
{
    unsigned long flags;

    spin_lock_irqsave(&entry->ds->lock, flags);
    BUG_ON(!entry->count);
    --entry->count;
    __sweep(entry->ds, head);
    spin_unlock_irqrestore(&entry->ds->lock, flags);
}
EXPORT_SYMBOL_GPL(dm_deferred_entry_dec);

/*
 * Returns 1 if deferred or 0 if no pending items to delay job.
 */
int dm_deferred_set_add_work(struct dm_deferred_set *ds, struct list_head *work)
{
    int r = 1;
    unsigned long flags;
    unsigned next_entry;

    spin_lock_irqsave(&ds->lock, flags);
    if ((ds->sweeper == ds->current_entry) &&
        !ds->entries[ds->current_entry].count)
        r = 0;
    else {
        list_add(work, &ds->entries[ds->current_entry].work_items);
        next_entry = ds_next(ds->current_entry);
        if (!ds->entries[next_entry].count)
            ds->current_entry = next_entry;
    }
    spin_unlock_irqrestore(&ds->lock, flags);

    return r;
}
EXPORT_SYMBOL_GPL(dm_deferred_set_add_work);

/*----------------------------------------------------------------*/

static int __init dm_bio_prison_init(void)
{
    _cell_cache = KMEM_CACHE(dm_bio_prison_cell, 0);
    if (!_cell_cache)
        return -ENOMEM;

    return 0;
}

static void __exit dm_bio_prison_exit(void)
{
    kmem_cache_destroy(_cell_cache);
    _cell_cache = NULL;
}

/*
 * module hooks
 */
module_init(dm_bio_prison_init);
module_exit(dm_bio_prison_exit);

MODULE_DESCRIPTION(DM_NAME " bio prison");
MODULE_AUTHOR("Joe Thornber <[email protected]>");
MODULE_LICENSE("GPL");