update bcache code, fsck improvements

[bcachefs-tools-debian] / libbcache / bcache.h

#ifndef _BCACHE_H
#define _BCACHE_H

/*
 * SOME HIGH LEVEL CODE DOCUMENTATION:
 *
 * Bcache mostly works with cache sets, cache devices, and backing devices.
 *
 * Support for multiple cache devices hasn't quite been finished off yet, but
 * it's about 95% plumbed through. A cache set and its cache devices is sort of
 * like a md raid array and its component devices. Most of the code doesn't care
 * about individual cache devices, the main abstraction is the cache set.
 *
 * Multiple cache devices is intended to give us the ability to mirror dirty
 * cached data and metadata, without mirroring clean cached data.
 *
 * Backing devices are different, in that they have a lifetime independent of a
 * cache set. When you register a newly formatted backing device it'll come up
 * in passthrough mode, and then you can attach and detach a backing device from
 * a cache set at runtime - while it's mounted and in use. Detaching implicitly
 * invalidates any cached data for that backing device.
 *
 * A cache set can have multiple (many) backing devices attached to it.
 *
 * There's also flash only volumes - this is the reason for the distinction
 * between struct cached_dev and struct bcache_device. A flash only volume
 * works much like a bcache device that has a backing device, except the
 * "cached" data is always dirty. The end result is that we get thin
 * provisioning with very little additional code.
 *
 * Flash only volumes work but they're not production ready because the moving
 * garbage collector needs more work. More on that later.
 *
 * BUCKETS/ALLOCATION:
 *
 * Bcache is primarily designed for caching, which means that in normal
 * operation all of our available space will be allocated. Thus, we need an
 * efficient way of deleting things from the cache so we can write new things to
 * it.
 *
 * To do this, we first divide the cache device up into buckets. A bucket is the
 * unit of allocation; they're typically around 1 mb - anywhere from 128k to 2M+
 * works efficiently.
 *
 * Each bucket has a 16 bit priority, and an 8 bit generation associated with
 * it. The gens and priorities for all the buckets are stored contiguously and
 * packed on disk (in a linked list of buckets - aside from the superblock, all
 * of bcache's metadata is stored in buckets).
 *
 * The priority is used to implement an LRU. We reset a bucket's priority when
 * we allocate it or on cache it, and every so often we decrement the priority
 * of each bucket. It could be used to implement something more sophisticated,
 * if anyone ever gets around to it.
 *
 * The generation is used for invalidating buckets. Each pointer also has an 8
 * bit generation embedded in it; for a pointer to be considered valid, its gen
 * must match the gen of the bucket it points into.  Thus, to reuse a bucket all
 * we have to do is increment its gen (and write its new gen to disk; we batch
 * this up).
 *
 * Bcache is entirely COW - we never write twice to a bucket, even buckets that
 * contain metadata (including btree nodes).
 *
 * THE BTREE:
 *
 * Bcache is in large part design around the btree.
 *
 * At a high level, the btree is just an index of key -> ptr tuples.
 *
 * Keys represent extents, and thus have a size field. Keys also have a variable
 * number of pointers attached to them (potentially zero, which is handy for
 * invalidating the cache).
 *
 * The key itself is an inode:offset pair. The inode number corresponds to a
 * backing device or a flash only volume. The offset is the ending offset of the
 * extent within the inode - not the starting offset; this makes lookups
 * slightly more convenient.
 *
 * Pointers contain the cache device id, the offset on that device, and an 8 bit
 * generation number. More on the gen later.
 *
 * Index lookups are not fully abstracted - cache lookups in particular are
 * still somewhat mixed in with the btree code, but things are headed in that
 * direction.
 *
 * Updates are fairly well abstracted, though. There are two different ways of
 * updating the btree; insert and replace.
 *
 * BTREE_INSERT will just take a list of keys and insert them into the btree -
 * overwriting (possibly only partially) any extents they overlap with. This is
 * used to update the index after a write.
 *
 * BTREE_REPLACE is really cmpxchg(); it inserts a key into the btree iff it is
 * overwriting a key that matches another given key. This is used for inserting
 * data into the cache after a cache miss, and for background writeback, and for
 * the moving garbage collector.
 *
 * There is no "delete" operation; deleting things from the index is
 * accomplished by either by invalidating pointers (by incrementing a bucket's
 * gen) or by inserting a key with 0 pointers - which will overwrite anything
 * previously present at that location in the index.
 *
 * This means that there are always stale/invalid keys in the btree. They're
 * filtered out by the code that iterates through a btree node, and removed when
 * a btree node is rewritten.
 *
 * BTREE NODES:
 *
 * Our unit of allocation is a bucket, and we we can't arbitrarily allocate and
 * free smaller than a bucket - so, that's how big our btree nodes are.
 *
 * (If buckets are really big we'll only use part of the bucket for a btree node
 * - no less than 1/4th - but a bucket still contains no more than a single
 * btree node. I'd actually like to change this, but for now we rely on the
 * bucket's gen for deleting btree nodes when we rewrite/split a node.)
 *
 * Anyways, btree nodes are big - big enough to be inefficient with a textbook
 * btree implementation.
 *
 * The way this is solved is that btree nodes are internally log structured; we
 * can append new keys to an existing btree node without rewriting it. This
 * means each set of keys we write is sorted, but the node is not.
 *
 * We maintain this log structure in memory - keeping 1Mb of keys sorted would
 * be expensive, and we have to distinguish between the keys we have written and
 * the keys we haven't. So to do a lookup in a btree node, we have to search
 * each sorted set. But we do merge written sets together lazily, so the cost of
 * these extra searches is quite low (normally most of the keys in a btree node
 * will be in one big set, and then there'll be one or two sets that are much
 * smaller).
 *
 * This log structure makes bcache's btree more of a hybrid between a
 * conventional btree and a compacting data structure, with some of the
 * advantages of both.
 *
 * GARBAGE COLLECTION:
 *
 * We can't just invalidate any bucket - it might contain dirty data or
 * metadata. If it once contained dirty data, other writes might overwrite it
 * later, leaving no valid pointers into that bucket in the index.
 *
 * Thus, the primary purpose of garbage collection is to find buckets to reuse.
 * It also counts how much valid data it each bucket currently contains, so that
 * allocation can reuse buckets sooner when they've been mostly overwritten.
 *
 * It also does some things that are really internal to the btree
 * implementation. If a btree node contains pointers that are stale by more than
 * some threshold, it rewrites the btree node to avoid the bucket's generation
 * wrapping around. It also merges adjacent btree nodes if they're empty enough.
 *
 * THE JOURNAL:
 *
 * Bcache's journal is not necessary for consistency; we always strictly
 * order metadata writes so that the btree and everything else is consistent on
 * disk in the event of an unclean shutdown, and in fact bcache had writeback
 * caching (with recovery from unclean shutdown) before journalling was
 * implemented.
 *
 * Rather, the journal is purely a performance optimization; we can't complete a
 * write until we've updated the index on disk, otherwise the cache would be
 * inconsistent in the event of an unclean shutdown. This means that without the
 * journal, on random write workloads we constantly have to update all the leaf
 * nodes in the btree, and those writes will be mostly empty (appending at most
 * a few keys each) - highly inefficient in terms of amount of metadata writes,
 * and it puts more strain on the various btree resorting/compacting code.
 *
 * The journal is just a log of keys we've inserted; on startup we just reinsert
 * all the keys in the open journal entries. That means that when we're updating
 * a node in the btree, we can wait until a 4k block of keys fills up before
 * writing them out.
 *
 * For simplicity, we only journal updates to leaf nodes; updates to parent
 * nodes are rare enough (since our leaf nodes are huge) that it wasn't worth
 * the complexity to deal with journalling them (in particular, journal replay)
 * - updates to non leaf nodes just happen synchronously (see btree_split()).
 */

#undef pr_fmt
#define pr_fmt(fmt) "bcache: %s() " fmt "\n", __func__

#include <linux/bug.h>
#include <linux/bcache.h>
#include <linux/bio.h>
#include <linux/kobject.h>
#include <linux/lglock.h>
#include <linux/list.h>
#include <linux/mutex.h>
#include <linux/percpu-refcount.h>
#include <linux/radix-tree.h>
#include <linux/rbtree.h>
#include <linux/rhashtable.h>
#include <linux/rwsem.h>
#include <linux/seqlock.h>
#include <linux/shrinker.h>
#include <linux/types.h>
#include <linux/workqueue.h>

#include "bset.h"
#include "fifo.h"
#include "util.h"
#include "closure.h"
#include "opts.h"

#include <linux/dynamic_fault.h>

#define cache_set_init_fault(name)                                      \
        dynamic_fault("bcache:cache_set_init:" name)
#define bch_meta_read_fault(name)                                       \
         dynamic_fault("bcache:meta:read:" name)
#define bch_meta_write_fault(name)                                      \
         dynamic_fault("bcache:meta:write:" name)

#ifndef bch_fmt
#define bch_fmt(_c, fmt)        "bcache (%s): " fmt "\n", ((_c)->name)
#endif

#define bch_info(c, fmt, ...) \
        printk(KERN_INFO bch_fmt(c, fmt), ##__VA_ARGS__)
#define bch_notice(c, fmt, ...) \
        printk(KERN_NOTICE bch_fmt(c, fmt), ##__VA_ARGS__)
#define bch_warn(c, fmt, ...) \
        printk(KERN_WARNING bch_fmt(c, fmt), ##__VA_ARGS__)
#define bch_err(c, fmt, ...) \
        printk(KERN_ERR bch_fmt(c, fmt), ##__VA_ARGS__)

#define bch_verbose(c, fmt, ...)                                        \
do {                                                                    \
        if ((c)->opts.verbose_recovery)                                 \
                bch_info(c, fmt, ##__VA_ARGS__);                        \
} while (0)

/* Parameters that are useful for debugging, but should always be compiled in: */
#define BCH_DEBUG_PARAMS_ALWAYS()                                       \
        BCH_DEBUG_PARAM(key_merging_disabled,                           \
                "Disables merging of extents")                          \
        BCH_DEBUG_PARAM(btree_gc_always_rewrite,                        \
                "Causes mark and sweep to compact and rewrite every "   \
                "btree node it traverses")                              \
        BCH_DEBUG_PARAM(btree_gc_rewrite_disabled,                      \
                "Disables rewriting of btree nodes during mark and sweep")\
        BCH_DEBUG_PARAM(btree_gc_coalesce_disabled,                     \
                "Disables coalescing of btree nodes")                   \
        BCH_DEBUG_PARAM(btree_shrinker_disabled,                        \
                "Disables the shrinker callback for the btree node cache")

/* Parameters that should only be compiled in in debug mode: */
#define BCH_DEBUG_PARAMS_DEBUG()                                        \
        BCH_DEBUG_PARAM(expensive_debug_checks,                         \
                "Enables various runtime debugging checks that "        \
                "significantly affect performance")                     \
        BCH_DEBUG_PARAM(debug_check_bkeys,                              \
                "Run bkey_debugcheck (primarily checking GC/allocation "\
                "information) when iterating over keys")                \
        BCH_DEBUG_PARAM(version_stress_test,                            \
                "Assigns random version numbers to newly written "      \
                "extents, to test overlapping extent cases")            \
        BCH_DEBUG_PARAM(verify_btree_ondisk,                            \
                "Reread btree nodes at various points to verify the "   \
                "mergesort in the read path against modifications "     \
                "done in memory")                                       \

#define BCH_DEBUG_PARAMS_ALL() BCH_DEBUG_PARAMS_ALWAYS() BCH_DEBUG_PARAMS_DEBUG()

#ifdef CONFIG_BCACHE_DEBUG
#define BCH_DEBUG_PARAMS() BCH_DEBUG_PARAMS_ALL()
#else
#define BCH_DEBUG_PARAMS() BCH_DEBUG_PARAMS_ALWAYS()
#endif

/* name, frequency_units, duration_units */
#define BCH_TIME_STATS()                                                \
        BCH_TIME_STAT(mca_alloc,                sec, us)                \
        BCH_TIME_STAT(mca_scan,                 sec, ms)                \
        BCH_TIME_STAT(btree_gc,                 sec, ms)                \
        BCH_TIME_STAT(btree_coalesce,           sec, ms)                \
        BCH_TIME_STAT(btree_split,              sec, us)                \
        BCH_TIME_STAT(btree_sort,               ms, us)                 \
        BCH_TIME_STAT(btree_read,               ms, us)                 \
        BCH_TIME_STAT(journal_write,            us, us)                 \
        BCH_TIME_STAT(journal_delay,            ms, us)                 \
        BCH_TIME_STAT(journal_blocked,          sec, ms)                \
        BCH_TIME_STAT(journal_flush_seq,        us, us)

#include "alloc_types.h"
#include "blockdev_types.h"
#include "buckets_types.h"
#include "clock_types.h"
#include "io_types.h"
#include "journal_types.h"
#include "keylist_types.h"
#include "keybuf_types.h"
#include "move_types.h"
#include "stats_types.h"
#include "super_types.h"

/* 256k, in sectors */
#define BTREE_NODE_SIZE_MAX             512

/*
 * Number of nodes we might have to allocate in a worst case btree split
 * operation - we split all the way up to the root, then allocate a new root.
 */
#define btree_reserve_required_nodes(depth)     (((depth) + 1) * 2 + 1)

/* Number of nodes btree coalesce will try to coalesce at once */
#define GC_MERGE_NODES          4U

/* Maximum number of nodes we might need to allocate atomically: */
#define BTREE_RESERVE_MAX                                               \
        (btree_reserve_required_nodes(BTREE_MAX_DEPTH) + GC_MERGE_NODES)

/* Size of the freelist we allocate btree nodes from: */
#define BTREE_NODE_RESERVE              (BTREE_RESERVE_MAX * 2)

struct btree;
struct cache;

enum gc_phase {
        GC_PHASE_PENDING_DELETE         = BTREE_ID_NR + 1,
        GC_PHASE_DONE
};

struct gc_pos {
        enum gc_phase           phase;
        struct bpos             pos;
        unsigned                level;
};

struct cache_member_cpu {
        u64                     nbuckets;       /* device size */
        u16                     first_bucket;   /* index of first bucket used */
        u16                     bucket_size;    /* sectors */
        u8                      state;
        u8                      tier;
        u8                      replication_set;
        u8                      has_metadata;
        u8                      has_data;
        u8                      replacement;
        u8                      discard;
        u8                      valid;
};

struct cache_member_rcu {
        struct rcu_head         rcu;
        unsigned                nr_in_set;
        struct cache_member_cpu m[];
};

/* cache->flags: */
enum {
        CACHE_DEV_REMOVING,
        CACHE_DEV_FORCE_REMOVE,
};

struct cache {
        struct percpu_ref       ref;
        struct rcu_head         free_rcu;
        struct work_struct      free_work;
        struct work_struct      remove_work;
        unsigned long           flags;

        struct cache_set        *set;

        struct cache_group      self;

        /*
         * Cached version of this device's member info from superblock
         * Committed by write_super()
         */
        struct {
                u8              nr_this_dev;
        }                       sb;
        struct cache_member_cpu mi;

        struct bcache_superblock disk_sb;

        struct kobject          kobj;

        /* biosets used in cloned bios for replicas and moving_gc */
        struct bio_set          replica_set;

        struct task_struct      *alloc_thread;

        struct prio_set         *disk_buckets;

        /*
         * When allocating new buckets, prio_write() gets first dibs - since we
         * may not be allocate at all without writing priorities and gens.
         * prio_last_buckets[] contains the last buckets we wrote priorities to
         * (so gc can mark them as metadata).
         */
        u64                     *prio_buckets;
        u64                     *prio_last_buckets;
        spinlock_t              prio_buckets_lock;
        struct bio              *bio_prio;

        /*
         * free: Buckets that are ready to be used
         *
         * free_inc: Incoming buckets - these are buckets that currently have
         * cached data in them, and we can't reuse them until after we write
         * their new gen to disk. After prio_write() finishes writing the new
         * gens/prios, they'll be moved to the free list (and possibly discarded
         * in the process)
         */
        DECLARE_FIFO(long, free)[RESERVE_NR];
        DECLARE_FIFO(long, free_inc);
        spinlock_t              freelist_lock;

        size_t                  fifo_last_bucket;

        /* Allocation stuff: */

        /* most out of date gen in the btree */
        u8                      *oldest_gens;
        struct bucket           *buckets;
        unsigned short          bucket_bits;    /* ilog2(bucket_size) */

        /* last calculated minimum prio */
        u16                     min_prio[2];

        /*
         * Bucket book keeping. The first element is updated by GC, the
         * second contains a saved copy of the stats from the beginning
         * of GC.
         */
        struct bucket_stats_cache __percpu *bucket_stats_percpu;
        struct bucket_stats_cache       bucket_stats_cached;

        atomic_long_t           saturated_count;
        size_t                  inc_gen_needs_gc;

        struct mutex            heap_lock;
        DECLARE_HEAP(struct bucket_heap_entry, heap);

        /* Moving GC: */
        struct task_struct      *moving_gc_read;

        struct bch_pd_controller moving_gc_pd;

        /* Tiering: */
        struct write_point      tiering_write_point;

        struct write_point      copygc_write_point;

        struct journal_device   journal;

        struct work_struct      io_error_work;

        /* The rest of this all shows up in sysfs */
#define IO_ERROR_SHIFT          20
        atomic_t                io_errors;
        atomic_t                io_count;

        atomic64_t              meta_sectors_written;
        atomic64_t              btree_sectors_written;
        u64 __percpu            *sectors_written;
};

/*
 * Flag bits for what phase of startup/shutdown the cache set is at, how we're
 * shutting down, etc.:
 *
 * CACHE_SET_UNREGISTERING means we're not just shutting down, we're detaching
 * all the backing devices first (their cached data gets invalidated, and they
 * won't automatically reattach).
 *
 * CACHE_SET_STOPPING always gets set first when we're closing down a cache set;
 * we'll continue to run normally for awhile with CACHE_SET_STOPPING set (i.e.
 * flushing dirty data).
 *
 * CACHE_SET_RUNNING means all cache devices have been registered and journal
 * replay is complete.
 */
enum {
        /* Startup: */
        CACHE_SET_INITIAL_GC_DONE,
        CACHE_SET_RUNNING,

        /* Shutdown: */
        CACHE_SET_UNREGISTERING,
        CACHE_SET_STOPPING,
        CACHE_SET_RO,
        CACHE_SET_RO_COMPLETE,
        CACHE_SET_EMERGENCY_RO,
        CACHE_SET_WRITE_DISABLE_COMPLETE,
        CACHE_SET_GC_STOPPING,
        CACHE_SET_GC_FAILURE,
        CACHE_SET_BDEV_MOUNTED,
        CACHE_SET_ERROR,
        CACHE_SET_FSCK_FIXED_ERRORS,
};

struct btree_debug {
        unsigned                id;
        struct dentry           *btree;
        struct dentry           *btree_format;
        struct dentry           *failed;
};

struct cache_set {
        struct closure          cl;

        struct list_head        list;
        struct kobject          kobj;
        struct kobject          internal;
        struct kobject          opts_dir;
        struct kobject          time_stats;
        struct completion       *stop_completion;
        unsigned long           flags;

        int                     minor;
        struct device           *chardev;
        struct super_block      *vfs_sb;
        char                    name[40];

        /* Counts outstanding writes, for clean transition to read-only */
        struct percpu_ref       writes;
        struct work_struct      read_only_work;

        struct cache __rcu      *cache[MAX_CACHES_PER_SET];

        struct mutex            mi_lock;
        struct cache_member_rcu __rcu *members;
        struct cache_member     *disk_mi; /* protected by register_lock */

        struct cache_set_opts   opts;

        /*
         * Cached copy in native endianness:
         * Set by cache_sb_to_cache_set:
         */
        struct {
                u16             block_size;
                u16             btree_node_size;

                u8              nr_in_set;
                u8              clean;

                u8              meta_replicas_have;
                u8              data_replicas_have;

                u8              str_hash_type;
        }                       sb;

        struct cache_sb         disk_sb;
        unsigned short          block_bits;     /* ilog2(block_size) */

        struct closure          sb_write;
        struct semaphore        sb_write_mutex;

        struct backing_dev_info bdi;

        /* BTREE CACHE */
        struct bio_set          btree_read_bio;

        struct btree_root       btree_roots[BTREE_ID_NR];
        struct mutex            btree_root_lock;

        bool                    btree_cache_table_init_done;
        struct rhashtable       btree_cache_table;

        /*
         * We never free a struct btree, except on shutdown - we just put it on
         * the btree_cache_freed list and reuse it later. This simplifies the
         * code, and it doesn't cost us much memory as the memory usage is
         * dominated by buffers that hold the actual btree node data and those
         * can be freed - and the number of struct btrees allocated is
         * effectively bounded.
         *
         * btree_cache_freeable effectively is a small cache - we use it because
         * high order page allocations can be rather expensive, and it's quite
         * common to delete and allocate btree nodes in quick succession. It
         * should never grow past ~2-3 nodes in practice.
         */
        struct mutex            btree_cache_lock;
        struct list_head        btree_cache;
        struct list_head        btree_cache_freeable;
        struct list_head        btree_cache_freed;

        /* Number of elements in btree_cache + btree_cache_freeable lists */
        unsigned                btree_cache_used;
        unsigned                btree_cache_reserve;
        struct shrinker         btree_cache_shrink;

        /*
         * If we need to allocate memory for a new btree node and that
         * allocation fails, we can cannibalize another node in the btree cache
         * to satisfy the allocation - lock to guarantee only one thread does
         * this at a time:
         */
        struct closure_waitlist mca_wait;
        struct task_struct      *btree_cache_alloc_lock;

        mempool_t               btree_reserve_pool;

        /*
         * Cache of allocated btree nodes - if we allocate a btree node and
         * don't use it, if we free it that space can't be reused until going
         * _all_ the way through the allocator (which exposes us to a livelock
         * when allocating btree reserves fail halfway through) - instead, we
         * can stick them here:
         */
        struct btree_alloc {
                struct open_bucket      *ob;
                BKEY_PADDED(k);
        }                       btree_reserve_cache[BTREE_NODE_RESERVE * 2];
        unsigned                btree_reserve_cache_nr;
        struct mutex            btree_reserve_cache_lock;

        mempool_t               btree_interior_update_pool;
        struct list_head        btree_interior_update_list;
        struct mutex            btree_interior_update_lock;

        struct workqueue_struct *wq;
        /* copygc needs its own workqueue for index updates.. */
        struct workqueue_struct *copygc_wq;

        /* ALLOCATION */
        struct bch_pd_controller foreground_write_pd;
        struct delayed_work     pd_controllers_update;
        unsigned                pd_controllers_update_seconds;
        spinlock_t              foreground_write_pd_lock;
        struct bch_write_op     *write_wait_head;
        struct bch_write_op     *write_wait_tail;

        struct timer_list       foreground_write_wakeup;

        /*
         * These contain all r/w devices - i.e. devices we can currently
         * allocate from:
         */
        struct cache_group      cache_all;
        struct cache_group      cache_tiers[CACHE_TIERS];

        u64                     capacity; /* sectors */

        /*
         * When capacity _decreases_ (due to a disk being removed), we
         * increment capacity_gen - this invalidates outstanding reservations
         * and forces them to be revalidated
         */
        u32                     capacity_gen;

        atomic64_t              sectors_available;

        struct bucket_stats_cache_set __percpu *bucket_stats_percpu;
        struct bucket_stats_cache_set   bucket_stats_cached;
        struct lglock           bucket_stats_lock;

        struct mutex            bucket_lock;

        struct closure_waitlist freelist_wait;


        /*
         * When we invalidate buckets, we use both the priority and the amount
         * of good data to determine which buckets to reuse first - to weight
         * those together consistently we keep track of the smallest nonzero
         * priority of any bucket.
         */
        struct prio_clock       prio_clock[2];

        struct io_clock         io_clock[2];

        /* SECTOR ALLOCATOR */
        struct list_head        open_buckets_open;
        struct list_head        open_buckets_free;
        unsigned                open_buckets_nr_free;
        struct closure_waitlist open_buckets_wait;
        spinlock_t              open_buckets_lock;
        struct open_bucket      open_buckets[OPEN_BUCKETS_COUNT];

        struct write_point      btree_write_point;

        struct write_point      write_points[WRITE_POINT_COUNT];
        struct write_point      promote_write_point;

        /*
         * This write point is used for migrating data off a device
         * and can point to any other device.
         * We can't use the normal write points because those will
         * gang up n replicas, and for migration we want only one new
         * replica.
         */
        struct write_point      migration_write_point;

        /* GARBAGE COLLECTION */
        struct task_struct      *gc_thread;
        atomic_t                kick_gc;

        /*
         * Tracks GC's progress - everything in the range [ZERO_KEY..gc_cur_pos]
         * has been marked by GC.
         *
         * gc_cur_phase is a superset of btree_ids (BTREE_ID_EXTENTS etc.)
         *
         * gc_cur_phase == GC_PHASE_DONE indicates that gc is finished/not
         * currently running, and gc marks are currently valid
         *
         * Protected by gc_pos_lock. Only written to by GC thread, so GC thread
         * can read without a lock.
         */
        seqcount_t              gc_pos_lock;
        struct gc_pos           gc_pos;

        /*
         * The allocation code needs gc_mark in struct bucket to be correct, but
         * it's not while a gc is in progress.
         */
        struct rw_semaphore     gc_lock;

        /* IO PATH */
        struct bio_set          bio_read;
        struct bio_set          bio_read_split;
        struct bio_set          bio_write;
        struct mutex            bio_bounce_pages_lock;
        mempool_t               bio_bounce_pages;

        mempool_t               lz4_workspace_pool;
        void                    *zlib_workspace;
        struct mutex            zlib_workspace_lock;
        mempool_t               compression_bounce[2];
        struct bio_decompress_worker __percpu
                                *bio_decompress_worker;

        /* For punting bio submissions to workqueue, io.c */
        struct bio_list         bio_submit_list;
        struct work_struct      bio_submit_work;
        spinlock_t              bio_submit_lock;

        struct bio_list         read_retry_list;
        struct work_struct      read_retry_work;
        spinlock_t              read_retry_lock;

        /* FILESYSTEM */
        wait_queue_head_t       writeback_wait;
        atomic_t                writeback_pages;
        unsigned                writeback_pages_max;
        atomic_long_t           nr_inodes;

        /* TIERING */
        struct task_struct      *tiering_read;
        struct bch_pd_controller tiering_pd;

        /* NOTIFICATIONS */
        struct mutex            uevent_lock;
        struct kobj_uevent_env  uevent_env;

        /* DEBUG JUNK */
        struct dentry           *debug;
        struct btree_debug      btree_debug[BTREE_ID_NR];
#ifdef CONFIG_BCACHE_DEBUG
        struct btree            *verify_data;
        struct btree_node       *verify_ondisk;
        struct mutex            verify_lock;
#endif

        u64                     unused_inode_hint;

        /*
         * A btree node on disk could have too many bsets for an iterator to fit
         * on the stack - have to dynamically allocate them
         */
        mempool_t               fill_iter;

        mempool_t               btree_bounce_pool;

        struct journal          journal;

        unsigned                bucket_journal_seq;

        /* CACHING OTHER BLOCK DEVICES */
        mempool_t               search;
        struct radix_tree_root  devices;
        struct list_head        cached_devs;
        u64                     cached_dev_sectors;
        struct closure          caching;

#define CONGESTED_MAX           1024
        unsigned                congested_last_us;
        atomic_t                congested;

        /* The rest of this all shows up in sysfs */
        unsigned                congested_read_threshold_us;
        unsigned                congested_write_threshold_us;

        struct cache_accounting accounting;
        atomic_long_t           cache_read_races;
        atomic_long_t           writeback_keys_done;
        atomic_long_t           writeback_keys_failed;

        unsigned                error_limit;
        unsigned                error_decay;

        unsigned                foreground_write_ratelimit_enabled:1;
        unsigned                copy_gc_enabled:1;
        unsigned                tiering_enabled:1;
        unsigned                tiering_percent;

        /*
         * foreground writes will be throttled when the number of free
         * buckets is below this percentage
         */
        unsigned                foreground_target_percent;

#define BCH_DEBUG_PARAM(name, description) bool name;
        BCH_DEBUG_PARAMS_ALL()
#undef BCH_DEBUG_PARAM

#define BCH_TIME_STAT(name, frequency_units, duration_units)            \
        struct time_stats       name##_time;
        BCH_TIME_STATS()
#undef BCH_TIME_STAT
};

static inline unsigned bucket_pages(const struct cache *ca)
{
        return ca->mi.bucket_size / PAGE_SECTORS;
}

static inline unsigned bucket_bytes(const struct cache *ca)
{
        return ca->mi.bucket_size << 9;
}

static inline unsigned block_bytes(const struct cache_set *c)
{
        return c->sb.block_size << 9;
}

#endif /* _BCACHE_H */