bcache: A block layer cache
Does writethrough and writeback caching, handles unclean shutdown, and
has a bunch of other nifty features motivated by real world usage.
See the wiki at http://bcache.evilpiepirate.org for more.
Signed-off-by: Kent Overstreet <koverstreet@google.com>
diff --git a/drivers/md/bcache/bcache.h b/drivers/md/bcache/bcache.h
new file mode 100644
index 0000000..d01a553
--- /dev/null
+++ b/drivers/md/bcache/bcache.h
@@ -0,0 +1,1232 @@
+#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()).
+ */
+
+#define pr_fmt(fmt) "bcache: %s() " fmt "\n", __func__
+
+#include <linux/bio.h>
+#include <linux/blktrace_api.h>
+#include <linux/kobject.h>
+#include <linux/list.h>
+#include <linux/mutex.h>
+#include <linux/rbtree.h>
+#include <linux/rwsem.h>
+#include <linux/types.h>
+#include <linux/workqueue.h>
+
+#include "util.h"
+#include "closure.h"
+
+struct bucket {
+ atomic_t pin;
+ uint16_t prio;
+ uint8_t gen;
+ uint8_t disk_gen;
+ uint8_t last_gc; /* Most out of date gen in the btree */
+ uint8_t gc_gen;
+ uint16_t gc_mark;
+};
+
+/*
+ * I'd use bitfields for these, but I don't trust the compiler not to screw me
+ * as multiple threads touch struct bucket without locking
+ */
+
+BITMASK(GC_MARK, struct bucket, gc_mark, 0, 2);
+#define GC_MARK_RECLAIMABLE 0
+#define GC_MARK_DIRTY 1
+#define GC_MARK_METADATA 2
+BITMASK(GC_SECTORS_USED, struct bucket, gc_mark, 2, 14);
+
+struct bkey {
+ uint64_t high;
+ uint64_t low;
+ uint64_t ptr[];
+};
+
+/* Enough for a key with 6 pointers */
+#define BKEY_PAD 8
+
+#define BKEY_PADDED(key) \
+ union { struct bkey key; uint64_t key ## _pad[BKEY_PAD]; }
+
+/* Version 1: Backing device
+ * Version 2: Seed pointer into btree node checksum
+ * Version 3: New UUID format
+ */
+#define BCACHE_SB_VERSION 3
+
+#define SB_SECTOR 8
+#define SB_SIZE 4096
+#define SB_LABEL_SIZE 32
+#define SB_JOURNAL_BUCKETS 256U
+/* SB_JOURNAL_BUCKETS must be divisible by BITS_PER_LONG */
+#define MAX_CACHES_PER_SET 8
+
+#define BDEV_DATA_START 16 /* sectors */
+
+struct cache_sb {
+ uint64_t csum;
+ uint64_t offset; /* sector where this sb was written */
+ uint64_t version;
+#define CACHE_BACKING_DEV 1
+
+ uint8_t magic[16];
+
+ uint8_t uuid[16];
+ union {
+ uint8_t set_uuid[16];
+ uint64_t set_magic;
+ };
+ uint8_t label[SB_LABEL_SIZE];
+
+ uint64_t flags;
+ uint64_t seq;
+ uint64_t pad[8];
+
+ uint64_t nbuckets; /* device size */
+ uint16_t block_size; /* sectors */
+ uint16_t bucket_size; /* sectors */
+
+ uint16_t nr_in_set;
+ uint16_t nr_this_dev;
+
+ uint32_t last_mount; /* time_t */
+
+ uint16_t first_bucket;
+ union {
+ uint16_t njournal_buckets;
+ uint16_t keys;
+ };
+ uint64_t d[SB_JOURNAL_BUCKETS]; /* journal buckets */
+};
+
+BITMASK(CACHE_SYNC, struct cache_sb, flags, 0, 1);
+BITMASK(CACHE_DISCARD, struct cache_sb, flags, 1, 1);
+BITMASK(CACHE_REPLACEMENT, struct cache_sb, flags, 2, 3);
+#define CACHE_REPLACEMENT_LRU 0U
+#define CACHE_REPLACEMENT_FIFO 1U
+#define CACHE_REPLACEMENT_RANDOM 2U
+
+BITMASK(BDEV_CACHE_MODE, struct cache_sb, flags, 0, 4);
+#define CACHE_MODE_WRITETHROUGH 0U
+#define CACHE_MODE_WRITEBACK 1U
+#define CACHE_MODE_WRITEAROUND 2U
+#define CACHE_MODE_NONE 3U
+BITMASK(BDEV_STATE, struct cache_sb, flags, 61, 2);
+#define BDEV_STATE_NONE 0U
+#define BDEV_STATE_CLEAN 1U
+#define BDEV_STATE_DIRTY 2U
+#define BDEV_STATE_STALE 3U
+
+/* Version 1: Seed pointer into btree node checksum
+ */
+#define BCACHE_BSET_VERSION 1
+
+/*
+ * This is the on disk format for btree nodes - a btree node on disk is a list
+ * of these; within each set the keys are sorted
+ */
+struct bset {
+ uint64_t csum;
+ uint64_t magic;
+ uint64_t seq;
+ uint32_t version;
+ uint32_t keys;
+
+ union {
+ struct bkey start[0];
+ uint64_t d[0];
+ };
+};
+
+/*
+ * On disk format for priorities and gens - see super.c near prio_write() for
+ * more.
+ */
+struct prio_set {
+ uint64_t csum;
+ uint64_t magic;
+ uint64_t seq;
+ uint32_t version;
+ uint32_t pad;
+
+ uint64_t next_bucket;
+
+ struct bucket_disk {
+ uint16_t prio;
+ uint8_t gen;
+ } __attribute((packed)) data[];
+};
+
+struct uuid_entry {
+ union {
+ struct {
+ uint8_t uuid[16];
+ uint8_t label[32];
+ uint32_t first_reg;
+ uint32_t last_reg;
+ uint32_t invalidated;
+
+ uint32_t flags;
+ /* Size of flash only volumes */
+ uint64_t sectors;
+ };
+
+ uint8_t pad[128];
+ };
+};
+
+BITMASK(UUID_FLASH_ONLY, struct uuid_entry, flags, 0, 1);
+
+#include "journal.h"
+#include "stats.h"
+struct search;
+struct btree;
+struct keybuf;
+
+struct keybuf_key {
+ struct rb_node node;
+ BKEY_PADDED(key);
+ void *private;
+};
+
+typedef bool (keybuf_pred_fn)(struct keybuf *, struct bkey *);
+
+struct keybuf {
+ keybuf_pred_fn *key_predicate;
+
+ struct bkey last_scanned;
+ spinlock_t lock;
+
+ /*
+ * Beginning and end of range in rb tree - so that we can skip taking
+ * lock and checking the rb tree when we need to check for overlapping
+ * keys.
+ */
+ struct bkey start;
+ struct bkey end;
+
+ struct rb_root keys;
+
+#define KEYBUF_NR 100
+ DECLARE_ARRAY_ALLOCATOR(struct keybuf_key, freelist, KEYBUF_NR);
+};
+
+struct bio_split_pool {
+ struct bio_set *bio_split;
+ mempool_t *bio_split_hook;
+};
+
+struct bio_split_hook {
+ struct closure cl;
+ struct bio_split_pool *p;
+ struct bio *bio;
+ bio_end_io_t *bi_end_io;
+ void *bi_private;
+};
+
+struct bcache_device {
+ struct closure cl;
+
+ struct kobject kobj;
+
+ struct cache_set *c;
+ unsigned id;
+#define BCACHEDEVNAME_SIZE 12
+ char name[BCACHEDEVNAME_SIZE];
+
+ struct gendisk *disk;
+
+ /* If nonzero, we're closing */
+ atomic_t closing;
+
+ /* If nonzero, we're detaching/unregistering from cache set */
+ atomic_t detaching;
+
+ atomic_long_t sectors_dirty;
+ unsigned long sectors_dirty_gc;
+ unsigned long sectors_dirty_last;
+ long sectors_dirty_derivative;
+
+ mempool_t *unaligned_bvec;
+ struct bio_set *bio_split;
+
+ unsigned data_csum:1;
+
+ int (*cache_miss)(struct btree *, struct search *,
+ struct bio *, unsigned);
+ int (*ioctl) (struct bcache_device *, fmode_t, unsigned, unsigned long);
+
+ struct bio_split_pool bio_split_hook;
+};
+
+struct io {
+ /* Used to track sequential IO so it can be skipped */
+ struct hlist_node hash;
+ struct list_head lru;
+
+ unsigned long jiffies;
+ unsigned sequential;
+ sector_t last;
+};
+
+struct cached_dev {
+ struct list_head list;
+ struct bcache_device disk;
+ struct block_device *bdev;
+
+ struct cache_sb sb;
+ struct bio sb_bio;
+ struct bio_vec sb_bv[1];
+ struct closure_with_waitlist sb_write;
+
+ /* Refcount on the cache set. Always nonzero when we're caching. */
+ atomic_t count;
+ struct work_struct detach;
+
+ /*
+ * Device might not be running if it's dirty and the cache set hasn't
+ * showed up yet.
+ */
+ atomic_t running;
+
+ /*
+ * Writes take a shared lock from start to finish; scanning for dirty
+ * data to refill the rb tree requires an exclusive lock.
+ */
+ struct rw_semaphore writeback_lock;
+
+ /*
+ * Nonzero, and writeback has a refcount (d->count), iff there is dirty
+ * data in the cache. Protected by writeback_lock; must have an
+ * shared lock to set and exclusive lock to clear.
+ */
+ atomic_t has_dirty;
+
+ struct ratelimit writeback_rate;
+ struct delayed_work writeback_rate_update;
+
+ /*
+ * Internal to the writeback code, so read_dirty() can keep track of
+ * where it's at.
+ */
+ sector_t last_read;
+
+ /* Number of writeback bios in flight */
+ atomic_t in_flight;
+ struct closure_with_timer writeback;
+ struct closure_waitlist writeback_wait;
+
+ struct keybuf writeback_keys;
+
+ /* For tracking sequential IO */
+#define RECENT_IO_BITS 7
+#define RECENT_IO (1 << RECENT_IO_BITS)
+ struct io io[RECENT_IO];
+ struct hlist_head io_hash[RECENT_IO + 1];
+ struct list_head io_lru;
+ spinlock_t io_lock;
+
+ struct cache_accounting accounting;
+
+ /* The rest of this all shows up in sysfs */
+ unsigned sequential_cutoff;
+ unsigned readahead;
+
+ unsigned sequential_merge:1;
+ unsigned verify:1;
+
+ unsigned writeback_metadata:1;
+ unsigned writeback_running:1;
+ unsigned char writeback_percent;
+ unsigned writeback_delay;
+
+ int writeback_rate_change;
+ int64_t writeback_rate_derivative;
+ uint64_t writeback_rate_target;
+
+ unsigned writeback_rate_update_seconds;
+ unsigned writeback_rate_d_term;
+ unsigned writeback_rate_p_term_inverse;
+ unsigned writeback_rate_d_smooth;
+};
+
+enum alloc_watermarks {
+ WATERMARK_PRIO,
+ WATERMARK_METADATA,
+ WATERMARK_MOVINGGC,
+ WATERMARK_NONE,
+ WATERMARK_MAX
+};
+
+struct cache {
+ struct cache_set *set;
+ struct cache_sb sb;
+ struct bio sb_bio;
+ struct bio_vec sb_bv[1];
+
+ struct kobject kobj;
+ struct block_device *bdev;
+
+ unsigned watermark[WATERMARK_MAX];
+
+ struct closure alloc;
+ struct workqueue_struct *alloc_workqueue;
+
+ struct closure prio;
+ 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_buckets[] contains the last buckets we wrote priorities to (so
+ * gc can mark them as metadata), prio_next[] contains the buckets
+ * allocated for the next prio write.
+ */
+ uint64_t *prio_buckets;
+ uint64_t *prio_last_buckets;
+
+ /*
+ * 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)
+ *
+ * unused: GC found nothing pointing into these buckets (possibly
+ * because all the data they contained was overwritten), so we only
+ * need to discard them before they can be moved to the free list.
+ */
+ DECLARE_FIFO(long, free);
+ DECLARE_FIFO(long, free_inc);
+ DECLARE_FIFO(long, unused);
+
+ size_t fifo_last_bucket;
+
+ /* Allocation stuff: */
+ struct bucket *buckets;
+
+ DECLARE_HEAP(struct bucket *, heap);
+
+ /*
+ * max(gen - disk_gen) for all buckets. When it gets too big we have to
+ * call prio_write() to keep gens from wrapping.
+ */
+ uint8_t need_save_prio;
+ unsigned gc_move_threshold;
+
+ /*
+ * If nonzero, we know we aren't going to find any buckets to invalidate
+ * until a gc finishes - otherwise we could pointlessly burn a ton of
+ * cpu
+ */
+ unsigned invalidate_needs_gc:1;
+
+ bool discard; /* Get rid of? */
+
+ /*
+ * We preallocate structs for issuing discards to buckets, and keep them
+ * on this list when they're not in use; do_discard() issues discards
+ * whenever there's work to do and is called by free_some_buckets() and
+ * when a discard finishes.
+ */
+ atomic_t discards_in_flight;
+ struct list_head discards;
+
+ struct journal_device journal;
+
+ /* The rest of this all shows up in sysfs */
+#define IO_ERROR_SHIFT 20
+ atomic_t io_errors;
+ atomic_t io_count;
+
+ atomic_long_t meta_sectors_written;
+ atomic_long_t btree_sectors_written;
+ atomic_long_t sectors_written;
+
+ struct bio_split_pool bio_split_hook;
+};
+
+struct gc_stat {
+ size_t nodes;
+ size_t key_bytes;
+
+ size_t nkeys;
+ uint64_t data; /* sectors */
+ uint64_t dirty; /* sectors */
+ unsigned in_use; /* percent */
+};
+
+/*
+ * Flag bits, for how the cache set is shutting down, and what phase it's at:
+ *
+ * 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_STOPPING_2 gets set at the last phase, when it's time to shut down the
+ * allocation thread.
+ */
+#define CACHE_SET_UNREGISTERING 0
+#define CACHE_SET_STOPPING 1
+#define CACHE_SET_STOPPING_2 2
+
+struct cache_set {
+ struct closure cl;
+
+ struct list_head list;
+ struct kobject kobj;
+ struct kobject internal;
+ struct dentry *debug;
+ struct cache_accounting accounting;
+
+ unsigned long flags;
+
+ struct cache_sb sb;
+
+ struct cache *cache[MAX_CACHES_PER_SET];
+ struct cache *cache_by_alloc[MAX_CACHES_PER_SET];
+ int caches_loaded;
+
+ struct bcache_device **devices;
+ struct list_head cached_devs;
+ uint64_t cached_dev_sectors;
+ struct closure caching;
+
+ struct closure_with_waitlist sb_write;
+
+ mempool_t *search;
+ mempool_t *bio_meta;
+ struct bio_set *bio_split;
+
+ /* For the btree cache */
+ struct shrinker shrink;
+
+ /* For the allocator itself */
+ wait_queue_head_t alloc_wait;
+
+ /* For the btree cache and anything allocation related */
+ struct mutex bucket_lock;
+
+ /* log2(bucket_size), in sectors */
+ unsigned short bucket_bits;
+
+ /* log2(block_size), in sectors */
+ unsigned short block_bits;
+
+ /*
+ * Default number of pages for a new btree node - may be less than a
+ * full bucket
+ */
+ unsigned btree_pages;
+
+ /*
+ * Lists of struct btrees; lru is the list for structs that have memory
+ * allocated for actual btree node, freed is for structs that do not.
+ *
+ * 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 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 bucket_cache_used;
+
+ /*
+ * 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. However, only one thread can be doing this
+ * at a time, for obvious reasons - try_harder and try_wait are
+ * basically a lock for this that we can wait on asynchronously. The
+ * btree_root() macro releases the lock when it returns.
+ */
+ struct closure *try_harder;
+ struct closure_waitlist try_wait;
+ uint64_t try_harder_start;
+
+ /*
+ * When we free a btree node, we increment the gen of the bucket the
+ * node is in - but we can't rewrite the prios and gens until we
+ * finished whatever it is we were doing, otherwise after a crash the
+ * btree node would be freed but for say a split, we might not have the
+ * pointers to the new nodes inserted into the btree yet.
+ *
+ * This is a refcount that blocks prio_write() until the new keys are
+ * written.
+ */
+ atomic_t prio_blocked;
+ struct closure_waitlist bucket_wait;
+
+ /*
+ * For any bio we don't skip we subtract the number of sectors from
+ * rescale; when it hits 0 we rescale all the bucket priorities.
+ */
+ atomic_t rescale;
+ /*
+ * 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.
+ */
+ uint16_t min_prio;
+
+ /*
+ * max(gen - gc_gen) for all buckets. When it gets too big we have to gc
+ * to keep gens from wrapping around.
+ */
+ uint8_t need_gc;
+ struct gc_stat gc_stats;
+ size_t nbuckets;
+
+ struct closure_with_waitlist gc;
+ /* Where in the btree gc currently is */
+ struct bkey gc_done;
+
+ /*
+ * The allocation code needs gc_mark in struct bucket to be correct, but
+ * it's not while a gc is in progress. Protected by bucket_lock.
+ */
+ int gc_mark_valid;
+
+ /* Counts how many sectors bio_insert has added to the cache */
+ atomic_t sectors_to_gc;
+
+ struct closure moving_gc;
+ struct closure_waitlist moving_gc_wait;
+ struct keybuf moving_gc_keys;
+ /* Number of moving GC bios in flight */
+ atomic_t in_flight;
+
+ struct btree *root;
+
+#ifdef CONFIG_BCACHE_DEBUG
+ struct btree *verify_data;
+ struct mutex verify_lock;
+#endif
+
+ unsigned nr_uuids;
+ struct uuid_entry *uuids;
+ BKEY_PADDED(uuid_bucket);
+ struct closure_with_waitlist uuid_write;
+
+ /*
+ * A btree node on disk could have too many bsets for an iterator to fit
+ * on the stack - this is a single element mempool for btree_read_work()
+ */
+ struct mutex fill_lock;
+ struct btree_iter *fill_iter;
+
+ /*
+ * btree_sort() is a merge sort and requires temporary space - single
+ * element mempool
+ */
+ struct mutex sort_lock;
+ struct bset *sort;
+
+ /* List of buckets we're currently writing data to */
+ struct list_head data_buckets;
+ spinlock_t data_bucket_lock;
+
+ struct journal journal;
+
+#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;
+
+ spinlock_t sort_time_lock;
+ struct time_stats sort_time;
+ struct time_stats btree_gc_time;
+ struct time_stats btree_split_time;
+ spinlock_t btree_read_time_lock;
+ struct time_stats btree_read_time;
+ struct time_stats try_harder_time;
+
+ 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 short journal_delay_ms;
+ unsigned verify:1;
+ unsigned key_merging_disabled:1;
+ unsigned gc_always_rewrite:1;
+ unsigned shrinker_disabled:1;
+ unsigned copy_gc_enabled:1;
+
+#define BUCKET_HASH_BITS 12
+ struct hlist_head bucket_hash[1 << BUCKET_HASH_BITS];
+};
+
+static inline bool key_merging_disabled(struct cache_set *c)
+{
+#ifdef CONFIG_BCACHE_DEBUG
+ return c->key_merging_disabled;
+#else
+ return 0;
+#endif
+}
+
+struct bbio {
+ unsigned submit_time_us;
+ union {
+ struct bkey key;
+ uint64_t _pad[3];
+ /*
+ * We only need pad = 3 here because we only ever carry around a
+ * single pointer - i.e. the pointer we're doing io to/from.
+ */
+ };
+ struct bio bio;
+};
+
+static inline unsigned local_clock_us(void)
+{
+ return local_clock() >> 10;
+}
+
+#define MAX_BSETS 4U
+
+#define BTREE_PRIO USHRT_MAX
+#define INITIAL_PRIO 32768
+
+#define btree_bytes(c) ((c)->btree_pages * PAGE_SIZE)
+#define btree_blocks(b) \
+ ((unsigned) (KEY_SIZE(&b->key) >> (b)->c->block_bits))
+
+#define btree_default_blocks(c) \
+ ((unsigned) ((PAGE_SECTORS * (c)->btree_pages) >> (c)->block_bits))
+
+#define bucket_pages(c) ((c)->sb.bucket_size / PAGE_SECTORS)
+#define bucket_bytes(c) ((c)->sb.bucket_size << 9)
+#define block_bytes(c) ((c)->sb.block_size << 9)
+
+#define __set_bytes(i, k) (sizeof(*(i)) + (k) * sizeof(uint64_t))
+#define set_bytes(i) __set_bytes(i, i->keys)
+
+#define __set_blocks(i, k, c) DIV_ROUND_UP(__set_bytes(i, k), block_bytes(c))
+#define set_blocks(i, c) __set_blocks(i, (i)->keys, c)
+
+#define node(i, j) ((struct bkey *) ((i)->d + (j)))
+#define end(i) node(i, (i)->keys)
+
+#define index(i, b) \
+ ((size_t) (((void *) i - (void *) (b)->sets[0].data) / \
+ block_bytes(b->c)))
+
+#define btree_data_space(b) (PAGE_SIZE << (b)->page_order)
+
+#define prios_per_bucket(c) \
+ ((bucket_bytes(c) - sizeof(struct prio_set)) / \
+ sizeof(struct bucket_disk))
+#define prio_buckets(c) \
+ DIV_ROUND_UP((size_t) (c)->sb.nbuckets, prios_per_bucket(c))
+
+#define JSET_MAGIC 0x245235c1a3625032ULL
+#define PSET_MAGIC 0x6750e15f87337f91ULL
+#define BSET_MAGIC 0x90135c78b99e07f5ULL
+
+#define jset_magic(c) ((c)->sb.set_magic ^ JSET_MAGIC)
+#define pset_magic(c) ((c)->sb.set_magic ^ PSET_MAGIC)
+#define bset_magic(c) ((c)->sb.set_magic ^ BSET_MAGIC)
+
+/* Bkey fields: all units are in sectors */
+
+#define KEY_FIELD(name, field, offset, size) \
+ BITMASK(name, struct bkey, field, offset, size)
+
+#define PTR_FIELD(name, offset, size) \
+ static inline uint64_t name(const struct bkey *k, unsigned i) \
+ { return (k->ptr[i] >> offset) & ~(((uint64_t) ~0) << size); } \
+ \
+ static inline void SET_##name(struct bkey *k, unsigned i, uint64_t v)\
+ { \
+ k->ptr[i] &= ~(~((uint64_t) ~0 << size) << offset); \
+ k->ptr[i] |= v << offset; \
+ }
+
+KEY_FIELD(KEY_PTRS, high, 60, 3)
+KEY_FIELD(HEADER_SIZE, high, 58, 2)
+KEY_FIELD(KEY_CSUM, high, 56, 2)
+KEY_FIELD(KEY_PINNED, high, 55, 1)
+KEY_FIELD(KEY_DIRTY, high, 36, 1)
+
+KEY_FIELD(KEY_SIZE, high, 20, 16)
+KEY_FIELD(KEY_INODE, high, 0, 20)
+
+/* Next time I change the on disk format, KEY_OFFSET() won't be 64 bits */
+
+static inline uint64_t KEY_OFFSET(const struct bkey *k)
+{
+ return k->low;
+}
+
+static inline void SET_KEY_OFFSET(struct bkey *k, uint64_t v)
+{
+ k->low = v;
+}
+
+PTR_FIELD(PTR_DEV, 51, 12)
+PTR_FIELD(PTR_OFFSET, 8, 43)
+PTR_FIELD(PTR_GEN, 0, 8)
+
+#define PTR_CHECK_DEV ((1 << 12) - 1)
+
+#define PTR(gen, offset, dev) \
+ ((((uint64_t) dev) << 51) | ((uint64_t) offset) << 8 | gen)
+
+static inline size_t sector_to_bucket(struct cache_set *c, sector_t s)
+{
+ return s >> c->bucket_bits;
+}
+
+static inline sector_t bucket_to_sector(struct cache_set *c, size_t b)
+{
+ return ((sector_t) b) << c->bucket_bits;
+}
+
+static inline sector_t bucket_remainder(struct cache_set *c, sector_t s)
+{
+ return s & (c->sb.bucket_size - 1);
+}
+
+static inline struct cache *PTR_CACHE(struct cache_set *c,
+ const struct bkey *k,
+ unsigned ptr)
+{
+ return c->cache[PTR_DEV(k, ptr)];
+}
+
+static inline size_t PTR_BUCKET_NR(struct cache_set *c,
+ const struct bkey *k,
+ unsigned ptr)
+{
+ return sector_to_bucket(c, PTR_OFFSET(k, ptr));
+}
+
+static inline struct bucket *PTR_BUCKET(struct cache_set *c,
+ const struct bkey *k,
+ unsigned ptr)
+{
+ return PTR_CACHE(c, k, ptr)->buckets + PTR_BUCKET_NR(c, k, ptr);
+}
+
+/* Btree key macros */
+
+/*
+ * The high bit being set is a relic from when we used it to do binary
+ * searches - it told you where a key started. It's not used anymore,
+ * and can probably be safely dropped.
+ */
+#define KEY(dev, sector, len) (struct bkey) \
+{ \
+ .high = (1ULL << 63) | ((uint64_t) (len) << 20) | (dev), \
+ .low = (sector) \
+}
+
+static inline void bkey_init(struct bkey *k)
+{
+ *k = KEY(0, 0, 0);
+}
+
+#define KEY_START(k) (KEY_OFFSET(k) - KEY_SIZE(k))
+#define START_KEY(k) KEY(KEY_INODE(k), KEY_START(k), 0)
+#define MAX_KEY KEY(~(~0 << 20), ((uint64_t) ~0) >> 1, 0)
+#define ZERO_KEY KEY(0, 0, 0)
+
+/*
+ * This is used for various on disk data structures - cache_sb, prio_set, bset,
+ * jset: The checksum is _always_ the first 8 bytes of these structs
+ */
+#define csum_set(i) \
+ crc64(((void *) (i)) + sizeof(uint64_t), \
+ ((void *) end(i)) - (((void *) (i)) + sizeof(uint64_t)))
+
+/* Error handling macros */
+
+#define btree_bug(b, ...) \
+do { \
+ if (bch_cache_set_error((b)->c, __VA_ARGS__)) \
+ dump_stack(); \
+} while (0)
+
+#define cache_bug(c, ...) \
+do { \
+ if (bch_cache_set_error(c, __VA_ARGS__)) \
+ dump_stack(); \
+} while (0)
+
+#define btree_bug_on(cond, b, ...) \
+do { \
+ if (cond) \
+ btree_bug(b, __VA_ARGS__); \
+} while (0)
+
+#define cache_bug_on(cond, c, ...) \
+do { \
+ if (cond) \
+ cache_bug(c, __VA_ARGS__); \
+} while (0)
+
+#define cache_set_err_on(cond, c, ...) \
+do { \
+ if (cond) \
+ bch_cache_set_error(c, __VA_ARGS__); \
+} while (0)
+
+/* Looping macros */
+
+#define for_each_cache(ca, cs, iter) \
+ for (iter = 0; ca = cs->cache[iter], iter < (cs)->sb.nr_in_set; iter++)
+
+#define for_each_bucket(b, ca) \
+ for (b = (ca)->buckets + (ca)->sb.first_bucket; \
+ b < (ca)->buckets + (ca)->sb.nbuckets; b++)
+
+static inline void __bkey_put(struct cache_set *c, struct bkey *k)
+{
+ unsigned i;
+
+ for (i = 0; i < KEY_PTRS(k); i++)
+ atomic_dec_bug(&PTR_BUCKET(c, k, i)->pin);
+}
+
+/* Blktrace macros */
+
+#define blktrace_msg(c, fmt, ...) \
+do { \
+ struct request_queue *q = bdev_get_queue(c->bdev); \
+ if (q) \
+ blk_add_trace_msg(q, fmt, ##__VA_ARGS__); \
+} while (0)
+
+#define blktrace_msg_all(s, fmt, ...) \
+do { \
+ struct cache *_c; \
+ unsigned i; \
+ for_each_cache(_c, (s), i) \
+ blktrace_msg(_c, fmt, ##__VA_ARGS__); \
+} while (0)
+
+static inline void cached_dev_put(struct cached_dev *dc)
+{
+ if (atomic_dec_and_test(&dc->count))
+ schedule_work(&dc->detach);
+}
+
+static inline bool cached_dev_get(struct cached_dev *dc)
+{
+ if (!atomic_inc_not_zero(&dc->count))
+ return false;
+
+ /* Paired with the mb in cached_dev_attach */
+ smp_mb__after_atomic_inc();
+ return true;
+}
+
+/*
+ * bucket_gc_gen() returns the difference between the bucket's current gen and
+ * the oldest gen of any pointer into that bucket in the btree (last_gc).
+ *
+ * bucket_disk_gen() returns the difference between the current gen and the gen
+ * on disk; they're both used to make sure gens don't wrap around.
+ */
+
+static inline uint8_t bucket_gc_gen(struct bucket *b)
+{
+ return b->gen - b->last_gc;
+}
+
+static inline uint8_t bucket_disk_gen(struct bucket *b)
+{
+ return b->gen - b->disk_gen;
+}
+
+#define BUCKET_GC_GEN_MAX 96U
+#define BUCKET_DISK_GEN_MAX 64U
+
+#define kobj_attribute_write(n, fn) \
+ static struct kobj_attribute ksysfs_##n = __ATTR(n, S_IWUSR, NULL, fn)
+
+#define kobj_attribute_rw(n, show, store) \
+ static struct kobj_attribute ksysfs_##n = \
+ __ATTR(n, S_IWUSR|S_IRUSR, show, store)
+
+/* Forward declarations */
+
+void bch_writeback_queue(struct cached_dev *);
+void bch_writeback_add(struct cached_dev *, unsigned);
+
+void bch_count_io_errors(struct cache *, int, const char *);
+void bch_bbio_count_io_errors(struct cache_set *, struct bio *,
+ int, const char *);
+void bch_bbio_endio(struct cache_set *, struct bio *, int, const char *);
+void bch_bbio_free(struct bio *, struct cache_set *);
+struct bio *bch_bbio_alloc(struct cache_set *);
+
+struct bio *bch_bio_split(struct bio *, int, gfp_t, struct bio_set *);
+void bch_generic_make_request(struct bio *, struct bio_split_pool *);
+void __bch_submit_bbio(struct bio *, struct cache_set *);
+void bch_submit_bbio(struct bio *, struct cache_set *, struct bkey *, unsigned);
+
+uint8_t bch_inc_gen(struct cache *, struct bucket *);
+void bch_rescale_priorities(struct cache_set *, int);
+bool bch_bucket_add_unused(struct cache *, struct bucket *);
+void bch_allocator_thread(struct closure *);
+
+long bch_bucket_alloc(struct cache *, unsigned, struct closure *);
+void bch_bucket_free(struct cache_set *, struct bkey *);
+
+int __bch_bucket_alloc_set(struct cache_set *, unsigned,
+ struct bkey *, int, struct closure *);
+int bch_bucket_alloc_set(struct cache_set *, unsigned,
+ struct bkey *, int, struct closure *);
+
+__printf(2, 3)
+bool bch_cache_set_error(struct cache_set *, const char *, ...);
+
+void bch_prio_write(struct cache *);
+void bch_write_bdev_super(struct cached_dev *, struct closure *);
+
+extern struct workqueue_struct *bcache_wq, *bch_gc_wq;
+extern const char * const bch_cache_modes[];
+extern struct mutex bch_register_lock;
+extern struct list_head bch_cache_sets;
+
+extern struct kobj_type bch_cached_dev_ktype;
+extern struct kobj_type bch_flash_dev_ktype;
+extern struct kobj_type bch_cache_set_ktype;
+extern struct kobj_type bch_cache_set_internal_ktype;
+extern struct kobj_type bch_cache_ktype;
+
+void bch_cached_dev_release(struct kobject *);
+void bch_flash_dev_release(struct kobject *);
+void bch_cache_set_release(struct kobject *);
+void bch_cache_release(struct kobject *);
+
+int bch_uuid_write(struct cache_set *);
+void bcache_write_super(struct cache_set *);
+
+int bch_flash_dev_create(struct cache_set *c, uint64_t size);
+
+int bch_cached_dev_attach(struct cached_dev *, struct cache_set *);
+void bch_cached_dev_detach(struct cached_dev *);
+void bch_cached_dev_run(struct cached_dev *);
+void bcache_device_stop(struct bcache_device *);
+
+void bch_cache_set_unregister(struct cache_set *);
+void bch_cache_set_stop(struct cache_set *);
+
+struct cache_set *bch_cache_set_alloc(struct cache_sb *);
+void bch_btree_cache_free(struct cache_set *);
+int bch_btree_cache_alloc(struct cache_set *);
+void bch_writeback_init_cached_dev(struct cached_dev *);
+void bch_moving_init_cache_set(struct cache_set *);
+
+void bch_cache_allocator_exit(struct cache *ca);
+int bch_cache_allocator_init(struct cache *ca);
+
+void bch_debug_exit(void);
+int bch_debug_init(struct kobject *);
+void bch_writeback_exit(void);
+int bch_writeback_init(void);
+void bch_request_exit(void);
+int bch_request_init(void);
+void bch_btree_exit(void);
+int bch_btree_init(void);
+
+#endif /* _BCACHE_H */