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forgot block_cache itself

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This commit is contained in:
Joe Thornber 2014-07-22 16:43:44 +01:00
parent d517684c95
commit d9040949fc
3 changed files with 936 additions and 0 deletions
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block-cache/block_cache.cc Normal file
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#include "block-cache/block_cache.h"
#include "block-cache/list.h"
#include <assert.h>
#include <libaio.h>
#include <errno.h>
#include <pthread.h>
#include <stdarg.h>
#include <stdio.h>
#include <string.h>
#include <unistd.h>
// FIXME: get from linux headers
#define SECTOR_SHIFT 9
#define PAGE_SIZE 4096
#define MIN_BLOCKS 16
#define WRITEBACK_LOW_THRESHOLD_PERCENT 33
#define WRITEBACK_HIGH_THRESHOLD_PERCENT 66
/*----------------------------------------------------------------
* Structures
*--------------------------------------------------------------*/
struct block_cache;
enum block_flags {
IO_PENDING = (1 << 0),
DIRTY = (1 << 1)
};
struct block {
struct list_head list;
struct list_head hash_list;
struct block_cache *bc;
unsigned ref_count;
int error;
unsigned flags;
struct iocb control_block;
struct bc_block b;
};
struct block_cache {
int fd;
sector_t block_size;
uint64_t nr_data_blocks;
uint64_t nr_cache_blocks;
void *blocks_memory;
void *blocks_data;
io_context_t aio_context;
struct io_event *events;
/*
* Blocks on the free list are not initialised, apart from the
* b.data field.
*/
struct list_head free;
struct list_head errored;
struct list_head dirty;
struct list_head clean;
unsigned nr_io_pending;
struct list_head io_pending;
unsigned nr_dirty;
/*
* Hash table fields.
*/
unsigned nr_buckets;
unsigned mask;
struct list_head buckets[0];
};
/*----------------------------------------------------------------
* Logging
*--------------------------------------------------------------*/
static void info(struct block_cache *bc, const char *format, ...)
__attribute__ ((format (printf, 2, 3)));
static void info(struct block_cache *bc, const char *format, ...)
{
va_list ap;
va_start(ap, format);
vfprintf(stderr, format, ap);
va_end(ap);
}
/*----------------------------------------------------------------
* Allocation
*--------------------------------------------------------------*/
static void *alloc_aligned(size_t len, size_t alignment)
{
void *result = NULL;
int r = posix_memalign(&result, alignment, len);
if (r)
return NULL;
return result;
}
static int init_free_list(struct block_cache *bc, unsigned count)
{
size_t len;
struct block *blocks;
size_t block_size = bc->block_size << SECTOR_SHIFT;
void *data;
unsigned i;
/* Allocate the block structures */
len = sizeof(struct block) * count;
blocks = static_cast<block *>(malloc(len));
if (!blocks)
return -ENOMEM;
bc->blocks_memory = blocks;
/* Allocate the data for each block. We page align the data. */
data = alloc_aligned(count * block_size, PAGE_SIZE);
if (!data) {
free(blocks);
return -ENOMEM;
}
bc->blocks_data = data;
for (i = 0; i < count; i++) {
struct block *b = blocks + i;
INIT_LIST_HEAD(&b->list);
b->b.data = data + block_size * i;
list_add(&b->list, &bc->free);
}
return 0;
}
static struct block *__alloc_block(struct block_cache *bc)
{
struct block *b;
if (list_empty(&bc->free))
return NULL;
b = list_first_entry(&bc->free, struct block, list);
list_del(&b->list);
return b;
}
/*----------------------------------------------------------------
* Flags handling
*--------------------------------------------------------------*/
static unsigned test_flags(struct block *b, unsigned flags)
{
return b->flags & flags;
}
static void clear_flags(struct block *b, unsigned flags)
{
b->flags &= ~flags;
}
static void set_flags(struct block *b, unsigned flags)
{
b->flags |= flags;
}
/*----------------------------------------------------------------
* Low level IO handling
*
* We cannot have two concurrent writes on the same block.
* eg, background writeback, put with dirty, flush?
*
* To avoid this we introduce some restrictions:
*
* i) A held block can never be written back.
* ii) You cannot get a block until writeback has completed.
*
*--------------------------------------------------------------*/
/*
* This can be called from the context of the aio thread. So we have a
* separate 'top half' complete function that we know is only called by the
* main cache thread.
*/
static void complete_io(struct block *b, int result)
{
b->error = result;
clear_flags(b, IO_PENDING);
b->bc->nr_io_pending--;
if (b->error)
list_move_tail(&b->list, &b->bc->errored);
else {
if (test_flags(b, DIRTY)) {
clear_flags(b, DIRTY);
b->bc->nr_dirty--;
}
list_move_tail(&b->list, &b->bc->clean);
}
}
/*
* |b->list| should be valid (either pointing to itself, on one of the other
* lists.
*/
static int issue_low_level(struct block *b, enum io_iocb_cmd opcode, const char *desc)
{
int r;
struct block_cache *bc = b->bc;
struct iocb *control_blocks[1];
assert(!test_flags(b, IO_PENDING));
set_flags(b, IO_PENDING);
bc->nr_io_pending++;
list_move_tail(&b->list, &bc->io_pending);
b->control_block.aio_lio_opcode = opcode;
control_blocks[0] = &b->control_block;
r = io_submit(bc->aio_context, 1, control_blocks);
if (r != 1) {
if (r < 0) {
perror("io_submit error");
info(bc, "io_submit failed with %s op: %d\n", desc, r);
} else
info(bc, "could not submit IOs, with %s op\n", desc);
complete_io(b, EIO);
return -EIO;
}
return 0;
}
static int issue_read(struct block *b)
{
return issue_low_level(b, IO_CMD_PREAD, "read");
}
static int issue_write(struct block *b)
{
return issue_low_level(b, IO_CMD_PWRITE, "write");
}
static void wait_io(struct block_cache *bc)
{
int r;
unsigned i;
// FIXME: use a timeout to prevent hanging
r = io_getevents(bc->aio_context, 1, bc->nr_cache_blocks, bc->events, NULL);
if (r < 0) {
info(bc, "io_getevents failed %d\n", r);
exit(1); /* FIXME: handle more gracefully */
}
for (i = 0; i < static_cast<unsigned>(r); i++) {
struct io_event *e = bc->events + i;
struct block *b = container_of(e->obj, struct block, control_block);
if (e->res == bc->block_size << SECTOR_SHIFT)
complete_io(b, 0);
else if (e->res < 0)
complete_io(b, e->res);
else {
info(bc, "incomplete io, unexpected\n");
}
}
}
/*----------------------------------------------------------------
* Clean/dirty list management
*--------------------------------------------------------------*/
/*
* We're using lru lists atm, but I think it would be worth
* experimenting with a multiqueue approach.
*/
static struct list_head *__categorise(struct block *b)
{
if (b->error)
return &b->bc->errored;
return (b->flags & DIRTY) ? &b->bc->dirty : &b->bc->clean;
}
static void hit(struct block *b)
{
list_move_tail(&b->list, __categorise(b));
}
/*----------------------------------------------------------------
* High level IO handling
*--------------------------------------------------------------*/
static void wait_all(struct block_cache *bc)
{
while (!list_empty(&bc->io_pending))
wait_io(bc);
}
static void wait_specific(struct block *b)
{
while (test_flags(b, IO_PENDING))
wait_io(b->bc);
}
static unsigned writeback(struct block_cache *bc, unsigned count)
{
int r;
struct block *b, *tmp;
unsigned actual = 0;
list_for_each_entry_safe (b, tmp, &bc->dirty, list) {
if (actual == count)
break;
if (b->ref_count)
continue;
r = issue_write(b);
if (!r)
actual++;
}
info(bc, "writeback: requested %u, actual %u\n", count, actual);
return actual;
}
/*----------------------------------------------------------------
* Hash table
*---------------------------------------------------------------*/
/*
* |nr_buckets| must be a power of two.
*/
static void hash_init(struct block_cache *bc, unsigned nr_buckets)
{
unsigned i;
bc->nr_buckets = nr_buckets;
bc->mask = nr_buckets - 1;
for (i = 0; i < nr_buckets; i++)
INIT_LIST_HEAD(bc->buckets + i);
}
static unsigned hash(struct block_cache *bc, uint64_t index)
{
const unsigned BIG_PRIME = 4294967291UL;
return (((unsigned) index) * BIG_PRIME) & bc->mask;
}
static struct block *hash_lookup(struct block_cache *bc, block_index index)
{
struct block *b;
unsigned bucket = hash(bc, index);
list_for_each_entry (b, bc->buckets + bucket, hash_list) {
if (b->b.index == index)
return b;
}
return NULL;
}
static void hash_insert(struct block *b)
{
unsigned bucket = hash(b->bc, b->b.index);
list_move_tail(&b->hash_list, b->bc->buckets + bucket);
}
static void hash_remove(struct block *b)
{
list_del_init(&b->hash_list);
}
/*----------------------------------------------------------------
* High level allocation
*--------------------------------------------------------------*/
static void setup_control_block(struct block *b)
{
struct iocb *cb = &b->control_block;
size_t block_size_bytes = b->bc->block_size << SECTOR_SHIFT;
memset(cb, 0, sizeof(*cb));
cb->aio_fildes = b->bc->fd;
cb->u.c.buf = b->b.data;
cb->u.c.offset = block_size_bytes * b->b.index;
cb->u.c.nbytes = block_size_bytes;
}
static struct block *new_block(struct block_cache *bc,
block_index index)
{
struct block *b;
b = __alloc_block(bc);
if (!b) {
if (list_empty(&bc->clean)) {
if (list_empty(&bc->io_pending))
writeback(bc, 9000);
wait_io(bc);
}
if (!list_empty(&bc->clean)) {
b = list_first_entry(&bc->clean, struct block, list);
hash_remove(b);
list_del(&b->list);
}
}
if (b) {
INIT_LIST_HEAD(&b->list);
INIT_LIST_HEAD(&b->hash_list);
b->bc = bc;
b->ref_count = 0;
b->error = 0;
clear_flags(b, IO_PENDING | DIRTY);
b->b.index = index;
setup_control_block(b);
hash_insert(b);
}
return b;
}
/*----------------------------------------------------------------
* Block reference counting
*--------------------------------------------------------------*/
static void get_block(struct block *b)
{
b->ref_count++;
}
static void put_block(struct block *b)
{
assert(b->ref_count);
b->ref_count--;
}
static void mark_dirty(struct block *b)
{
struct block_cache *bc = b->bc;
if (!test_flags(b, DIRTY)) {
set_flags(b, DIRTY);
list_move_tail(&b->list, &b->bc->dirty);
bc->nr_dirty++;
}
}
/*----------------------------------------------------------------
* Public interface
*--------------------------------------------------------------*/
unsigned calc_nr_cache_blocks(size_t mem, sector_t block_size)
{
size_t space_per_block = (block_size << SECTOR_SHIFT) + sizeof(struct block);
unsigned r = mem / space_per_block;
return (r < MIN_BLOCKS) ? MIN_BLOCKS : r;
}
unsigned calc_nr_buckets(unsigned nr_blocks)
{
unsigned r = 8;
unsigned n = nr_blocks / 4;
if (n < 8)
n = 8;
while (r < n)
r <<= 1;
return r;
}
void
block_cache_destroy(struct block_cache *bc)
{
wait_all(bc);
if (bc->aio_context)
io_destroy(bc->aio_context);
if (bc->events)
free(bc->events);
if (bc->blocks_memory)
free(bc->blocks_memory);
if (bc->blocks_data)
free(bc->blocks_data);
free(bc);
}
struct block_cache *
block_cache_create(int fd, sector_t block_size, uint64_t on_disk_blocks, size_t mem)
{
int r;
struct block_cache *bc;
unsigned nr_cache_blocks = calc_nr_cache_blocks(mem, block_size);
unsigned nr_buckets = calc_nr_buckets(nr_cache_blocks);
bc = static_cast<block_cache *>(malloc(sizeof(*bc) + sizeof(*bc->buckets) * nr_buckets));
if (bc) {
memset(bc, 0, sizeof(*bc));
bc->fd = fd;
bc->block_size = block_size;
bc->nr_data_blocks = on_disk_blocks;
bc->nr_cache_blocks = nr_cache_blocks;
bc->events = static_cast<io_event *>(malloc(sizeof(*bc->events) * nr_cache_blocks));
if (!bc->events) {
info(bc, "couldn't allocate events array\n");
goto bad;
}
bc->aio_context = 0; /* needed or io_setup will fail */
r = io_setup(nr_cache_blocks, &bc->aio_context);
if (r < 0) {
info(bc, "io_setup failed: %d\n", r);
goto bad;
}
hash_init(bc, nr_buckets);
INIT_LIST_HEAD(&bc->free);
INIT_LIST_HEAD(&bc->errored);
INIT_LIST_HEAD(&bc->dirty);
INIT_LIST_HEAD(&bc->clean);
INIT_LIST_HEAD(&bc->io_pending);
r = init_free_list(bc, nr_cache_blocks);
if (r) {
info(bc, "couldn't allocate blocks: %d\n", r);
goto bad;
}
}
return bc;
bad:
block_cache_destroy(bc);
return NULL;
}
uint64_t block_cache_get_nr_blocks(struct block_cache *bc)
{
return bc->nr_data_blocks;
}
static void zero_block(struct block *b)
{
memset(b->b.data, 0, b->bc->block_size << SECTOR_SHIFT);
mark_dirty(b);
}
static struct block *lookup_or_read_block(struct block_cache *bc, block_index index, unsigned flags)
{
struct block *b = hash_lookup(bc, index);
if (b) {
if (test_flags(b, IO_PENDING))
wait_specific(b);
if (flags & GF_ZERO)
zero_block(b);
} else {
if (flags & GF_CAN_BLOCK) {
b = new_block(bc, index);
if (b) {
if (flags & GF_ZERO)
zero_block(b);
else {
issue_read(b);
wait_specific(b);
}
}
}
}
return (!b || b->error) ? NULL : b;
}
struct bc_block *
block_cache_get(struct block_cache *bc, block_index index, unsigned flags)
{
struct block *b = lookup_or_read_block(bc, index, flags);
if (b) {
hit(b);
get_block(b);
return &b->b;
}
return NULL;
}
void
block_cache_put(struct bc_block *bcb, unsigned flags)
{
unsigned nr_available;
struct block *b = container_of(bcb, struct block, b);
struct block_cache *bc = b->bc;
put_block(b);
if (flags & PF_DIRTY) {
mark_dirty(b);
nr_available = bc->nr_cache_blocks - (bc->nr_dirty - bc->nr_io_pending);
if (nr_available < (WRITEBACK_LOW_THRESHOLD_PERCENT * bc->nr_cache_blocks / 100))
writeback(bc, (WRITEBACK_HIGH_THRESHOLD_PERCENT * bc->nr_cache_blocks / 100) - nr_available);
}
}
int
block_cache_flush(struct block_cache *bc)
{
struct block *b;
list_for_each_entry (b, &bc->dirty, list) {
if (b->ref_count) {
info(bc, "attempt to lock an already locked block\n");
return -EAGAIN;
}
issue_write(b);
}
wait_all(bc);
return list_empty(&bc->errored) ? 0 : -EIO;
}
void
block_cache_prefetch(struct block_cache *bc, block_index index)
{
struct block *b = hash_lookup(bc, index);
if (!b) {
b = new_block(bc, index);
if (b)
issue_read(b);
}
}
/*----------------------------------------------------------------*/

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block-cache/block_cache.h Normal file
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#ifndef BLOCK_CACHE_H
#define BLOCK_CACHE_H
#include <stdint.h>
#include <stdlib.h>
/*----------------------------------------------------------------*/
/* FIXME: add logging */
/*----------------------------------------------------------------*/
/*
* This library is not thread-safe.
*/
typedef uint64_t block_index;
struct block_cache;
struct bc_block {
block_index index;
void *data;
};
typedef uint64_t sector_t;
struct block_cache *block_cache_create(int fd, sector_t block_size,
uint64_t max_nr_blocks, size_t mem);
void block_cache_destroy(struct block_cache *bc);
uint64_t block_cache_get_nr_blocks(struct block_cache *bc);
enum get_flags {
GF_ZERO = (1 << 0),
GF_CAN_BLOCK = (1 << 1)
};
struct bc_block *block_cache_get(struct block_cache *bc, block_index index, unsigned flags);
enum put_flags {
PF_DIRTY = (1 << 0),
};
void block_cache_put(struct bc_block *b, unsigned flags);
/*
* Flush can fail if an earlier write failed. You do not know which block
* failed. Make sure you build your recovery with this in mind.
*/
int block_cache_flush(struct block_cache *bc);
void block_cache_prefetch(struct block_cache *bc, block_index index);
/*----------------------------------------------------------------*/
#endif

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block-cache/list.h Normal file
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#ifndef LIB_BLOCK_CACHE_LIST_H
#define LIB_BLOCK_CACHE_LIST_H
#include <stddef.h>
/*----------------------------------------------------------------*/
/*
* Simple intrusive linked list code. Lifted from Linux kernel.
*/
/**
* container_of - cast a member of a structure out to the containing structure
* @ptr: the pointer to the member.
* @type: the type of the container struct this is embedded in.
* @member: the name of the member within the struct.
*
*/
#define container_of(ptr, type, member) ({ \
const typeof( ((type *)0)->member ) *__mptr = (ptr); \
(type *)( (char *)__mptr - offsetof(type,member) );})
struct list_head {
struct list_head *next, *prev;
};
static inline void INIT_LIST_HEAD(struct list_head *list)
{
list->next = list;
list->prev = list;
}
static inline void __list_add(struct list_head *new_,
struct list_head *prev,
struct list_head *next)
{
next->prev = new_;
new_->next = next;
new_->prev = prev;
prev->next = new_;
}
/**
* list_add - add a new entry
* @new_: new entry to be added
* @head: list head to add it after
*
* Insert a new entry after the specified head.
* This is good for implementing stacks.
*/
static inline void list_add(struct list_head *new_, struct list_head *head)
{
__list_add(new_, head, head->next);
}
/**
* list_add_tail - add a new entry
* @new_: new entry to be added
* @head: list head to add it before
*
* Insert a new entry before the specified head.
* This is useful for implementing queues.
*/
static inline void list_add_tail(struct list_head *new_, struct list_head *head)
{
__list_add(new_, head->prev, head);
}
/*
* Delete a list entry by making the prev/next entries
* point to each other.
*
* This is only for internal list manipulation where we know
* the prev/next entries already!
*/
static inline void __list_del(struct list_head * prev, struct list_head * next)
{
next->prev = prev;
prev->next = next;
}
/**
* list_del - deletes entry from list.
* @entry: the element to delete from the list.
* Note: list_empty() on entry does not return true after this, the entry is
* in an undefined state.
*/
static inline void __list_del_entry(struct list_head *entry)
{
__list_del(entry->prev, entry->next);
}
static inline void list_del(struct list_head *entry)
{
__list_del(entry->prev, entry->next);
entry->next = NULL;
entry->prev = NULL;
}
/**
* list_del_init - deletes entry from list and reinitialize it.
* @entry: the element to delete from the list.
*/
static inline void list_del_init(struct list_head *entry)
{
__list_del_entry(entry);
INIT_LIST_HEAD(entry);
}
/**
* list_move - delete from one list and add as another's head
* @list: the entry to move
* @head: the head that will precede our entry
*/
static inline void list_move(struct list_head *list, struct list_head *head)
{
__list_del_entry(list);
list_add(list, head);
}
/**
* list_move_tail - delete from one list and add as another's tail
* @list: the entry to move
* @head: the head that will follow our entry
*/
static inline void list_move_tail(struct list_head *list,
struct list_head *head)
{
__list_del_entry(list);
list_add_tail(list, head);
}
/**
* list_empty - tests whether a list is empty
* @head: the list to test.
*/
static inline int list_empty(const struct list_head *head)
{
return head->next == head;
}
/**
* list_entry - get the struct for this entry
* @ptr: the &struct list_head pointer.
* @type: the type of the struct this is embedded in.
* @member: the name of the list_struct within the struct.
*/
#define list_entry(ptr, type, member) \
container_of(ptr, type, member)
/**
* list_first_entry - get the first element from a list
* @ptr: the list head to take the element from.
* @type: the type of the struct this is embedded in.
* @member: the name of the list_struct within the struct.
*
* Note, that list is expected to be not empty.
*/
#define list_first_entry(ptr, type, member) \
list_entry((ptr)->next, type, member)
/**
* list_next_entry - get the next element in list
* @pos: the type * to cursor
* @member: the name of the list_struct within the struct.
*/
#define list_next_entry(pos, member) \
list_entry((pos)->member.next, typeof(*(pos)), member)
/**
* list_for_each - iterate over a list
* @pos: the &struct list_head to use as a loop cursor.
* @head: the head for your list.
*/
#define list_for_each(pos, head) \
for (pos = (head)->next; pos != (head); pos = pos->next)
/**
* list_for_each_safe - iterate over a list safe against removal of list entry
* @pos: the &struct list_head to use as a loop cursor.
* @n: another &struct list_head to use as temporary storage
* @head: the head for your list.
*/
#define list_for_each_safe(pos, n, head) \
for (pos = (head)->next, n = pos->next; pos != (head); \
pos = n, n = pos->next)
/**
* list_for_each_entry - iterate over list of given type
* @pos: the type * to use as a loop cursor.
* @head: the head for your list.
* @member: the name of the list_struct within the struct.
*/
#define list_for_each_entry(pos, head, member) \
for (pos = list_first_entry(head, typeof(*pos), member); \
&pos->member != (head); \
pos = list_next_entry(pos, member))
/**
* list_for_each_entry_safe - iterate over list of given type safe against removal of list entry
* @pos: the type * to use as a loop cursor.
* @n: another type * to use as temporary storage
* @head: the head for your list.
* @member: the name of the list_struct within the struct.
*/
#define list_for_each_entry_safe(pos, n, head, member) \
for (pos = list_first_entry(head, typeof(*pos), member), \
n = list_next_entry(pos, member); \
&pos->member != (head); \
pos = n, n = list_next_entry(n, member))
/*----------------------------------------------------------------*/
#endif