thin-provisioning-tools/block-cache/block_cache.cc

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#include "block-cache/block_cache.h"
#include <algorithm>
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#include <assert.h>
#include <libaio.h>
#include <errno.h>
#include <pthread.h>
#include <stdarg.h>
#include <stdio.h>
#include <string.h>
#include <unistd.h>
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#include <iostream>
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#include <stdexcept>
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#include <sstream>
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using namespace bcache;
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//----------------------------------------------------------------
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// 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
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//----------------------------------------------------------------
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namespace {
void *alloc_aligned(size_t len, size_t alignment)
{
void *result = NULL;
int r = posix_memalign(&result, alignment, len);
if (r)
return NULL;
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return result;
}
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}
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//----------------------------------------------------------------
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int
block_cache::init_free_list(unsigned count)
{
size_t block_size = block_size_ << SECTOR_SHIFT;
unsigned char *data = static_cast<unsigned char *>(alloc_aligned(count * block_size, PAGE_SIZE));
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/* Allocate the data for each block. We page align the data. */
if (!data)
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return -ENOMEM;
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blocks_data_ = data;
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for (unsigned i = 0; i < count; i++) {
block &b = (*blocks_memory_)[i];
b.data_ = data + (block_size * i);
free_.push_front(b);
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}
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return 0;
}
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void
block_cache::exit_free_list()
{
if (blocks_data_)
free(blocks_data_);
}
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block_cache::block *
block_cache::__alloc_block()
{
if (free_.empty())
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return NULL;
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block &b = free_.front();
b.unlink();
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return &b;
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}
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/*----------------------------------------------------------------
* 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.
*/
void
block_cache::complete_io(block &b, int result)
{
b.error_ = result;
b.clear_flags(BF_IO_PENDING);
if (b.error_) {
b.unlink();
errored_.push_back(b);
} else {
if (b.test_flags(BF_DIRTY))
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b.clear_flags(BF_DIRTY | BF_PREVIOUSLY_DIRTY);
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b.unlink();
clean_.push_back(b);
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}
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}
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/*
* |b->list| should be valid (either pointing to itself, on one of the other
* lists.
*/
// FIXME: add batch issue
void
block_cache::issue_low_level(block &b, enum io_iocb_cmd opcode, const char *desc)
{
int r;
iocb *control_blocks[1];
assert(!b.test_flags(BF_IO_PENDING));
b.set_flags(BF_IO_PENDING);
b.unlink();
io_pending_.push_back(b);
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b.control_block_.aio_lio_opcode = opcode;
control_blocks[0] = &b.control_block_;
r = io_submit(aio_context_, 1, control_blocks);
if (r != 1) {
complete_io(b, EIO);
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std::ostringstream out;
out << "couldn't issue " << desc << " io for block " << b.index_;
if (r < 0)
out << ": io_submit failed with " << r;
else
out << ": io_submit succeeded, but queued no io";
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throw std::runtime_error(out.str());
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}
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}
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void
block_cache::issue_read(block &b)
{
assert(!b.test_flags(BF_IO_PENDING));
issue_low_level(b, IO_CMD_PREAD, "read");
}
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void
block_cache::issue_write(block &b)
{
assert(!b.test_flags(BF_IO_PENDING));
b.v_->prepare(b.data_, b.index_);
issue_low_level(b, IO_CMD_PWRITE, "write");
}
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void
block_cache::wait_io()
{
int r;
unsigned i;
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// FIXME: use a timeout to prevent hanging
r = io_getevents(aio_context_, 1, nr_cache_blocks_, &events_[0], NULL);
if (r < 0) {
std::ostringstream out;
out << "io_getevents failed: " << r;
throw std::runtime_error(out.str());
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}
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for (i = 0; i < static_cast<unsigned>(r); i++) {
io_event const &e = events_[i];
block *b = base::container_of(e.obj, &block::control_block_);
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if (e.res == block_size_ << SECTOR_SHIFT)
complete_io(*b, 0);
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else if (static_cast<long>(e.res) < 0)
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complete_io(*b, e.res);
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else {
std::ostringstream out;
out << "incomplete io for block " << b->index_
<< ", e.res = " << e.res
<< ", e.res2 = " << e.res2
<< ", offset = " << b->control_block_.u.c.offset
<< ", nbytes = " << b->control_block_.u.c.nbytes;
throw std::runtime_error(out.str());
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}
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}
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}
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/*----------------------------------------------------------------
* Clean/dirty list management
*--------------------------------------------------------------*/
/*
* We're using lru lists atm, but I think it would be worth
* experimenting with a multiqueue approach.
*/
block_cache::block_list &
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block_cache::__categorise(block &b)
{
if (b.error_)
return errored_;
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return b.test_flags(BF_DIRTY) ? dirty_ : clean_;
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}
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void
block_cache::hit(block &b)
{
b.unlink();
__categorise(b).push_back(b);
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}
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/*----------------------------------------------------------------
* High level IO handling
*--------------------------------------------------------------*/
void
block_cache::wait_all()
{
while (!io_pending_.empty())
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wait_io();
}
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void
block_cache::wait_specific(block &b)
{
while (b.test_flags(BF_IO_PENDING))
wait_io();
}
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unsigned
block_cache::writeback(unsigned count)
{
unsigned actual = 0, dirty_length = 0;
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// issue_write unlinks b, which invalidates the iteration, so we
// keep track of the next element before removing.
auto it = dirty_.begin();
auto next = it;
while (it != dirty_.end()) {
next = it;
++next;
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dirty_length++;
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if (actual == count)
break;
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// The block may be on the dirty list from a prior
// acquisition.
if (it->ref_count_)
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continue;
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issue_write(*it);
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actual++;
it = next;
}
return actual;
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}
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/*----------------------------------------------------------------
* High level allocation
*--------------------------------------------------------------*/
void
block_cache::setup_control_block(block &b)
{
iocb *cb = &b.control_block_;
size_t block_size_bytes = block_size_ << SECTOR_SHIFT;
memset(cb, 0, sizeof(*cb));
cb->aio_fildes = fd_;
cb->u.c.buf = b.data_;
cb->u.c.offset = block_size_bytes * b.index_;
cb->u.c.nbytes = block_size_bytes;
}
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// FIXME: return a reference
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block_cache::block *
block_cache::find_unused_clean_block()
{
for (block &b : clean_) {
if (b.ref_count_)
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continue;
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b.unlink_set();
b.unlink();
return &b;
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}
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return NULL;
}
block_cache::block *
block_cache::new_block(block_address index)
{
block *b;
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b = __alloc_block();
while (!b && nr_locked_ < nr_cache_blocks_) {
b = find_unused_clean_block();
if (!b) {
if (io_pending_.empty())
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writeback(16);
wait_io();
}
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}
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if (b) {
b->bc_ = this;
b->ref_count_ = 0;
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b->error_ = 0;
b->flags_ = 0;
b->v_ = noop_validator_;
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b->index_ = index;
setup_control_block(*b);
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block_set_.insert(*b);
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}
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return b;
}
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/*----------------------------------------------------------------
* Block reference counting
*--------------------------------------------------------------*/
unsigned
block_cache::calc_nr_cache_blocks(size_t mem, sector_t block_size)
{
size_t space_per_block = (block_size << SECTOR_SHIFT) + sizeof(block);
unsigned r = mem / space_per_block;
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return (r < MIN_BLOCKS) ? MIN_BLOCKS : r;
}
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unsigned
block_cache::calc_nr_buckets(unsigned nr_blocks)
{
unsigned r = 8;
unsigned n = nr_blocks / 4;
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if (n < 8)
n = 8;
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while (r < n)
r <<= 1;
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return r;
}
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block_cache::block_cache(int fd, sector_t block_size, uint64_t on_disk_blocks, size_t mem)
: nr_locked_(0),
read_hits_(0),
read_misses_(0),
write_zeroes_(0),
write_hits_(0),
write_misses_(0),
prefetches_(0),
noop_validator_(new noop_validator())
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{
int r;
unsigned nr_cache_blocks = calc_nr_cache_blocks(mem, block_size);
fd_ = fd;
block_size_ = block_size;
nr_data_blocks_ = on_disk_blocks;
nr_cache_blocks_ = nr_cache_blocks;
events_.resize(nr_cache_blocks);
aio_context_ = 0; /* needed or io_setup will fail */
r = io_setup(nr_cache_blocks, &aio_context_);
if (r < 0) {
perror("io_setup failed");
throw std::runtime_error("io_setup failed");
}
blocks_memory_.reset(new std::vector<block>(nr_cache_blocks));
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r = init_free_list(nr_cache_blocks);
if (r)
throw std::runtime_error("couldn't allocate blocks");
}
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block_cache::~block_cache()
{
assert(!nr_locked_);
flush();
wait_all();
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exit_free_list();
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if (aio_context_)
io_destroy(aio_context_);
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::close(fd_);
#if 0
std::cerr << "\nblock cache stats\n"
<< "=================\n"
<< "prefetches:\t" << prefetches_ << "\n"
<< "read hits:\t" << read_hits_ << "\n"
<< "read misses:\t" << read_misses_ << "\n"
<< "write hits:\t" << write_hits_ << "\n"
<< "write misses:\t" << write_misses_ << "\n"
<< "write zeroes:\t" << write_zeroes_ << std::endl;
#endif
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}
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uint64_t
block_cache::get_nr_blocks() const
{
return nr_data_blocks_;
}
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uint64_t
block_cache::get_nr_locked() const
{
return nr_locked_;
}
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void
block_cache::zero_block(block &b)
{
write_zeroes_++;
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memset(b.data_, 0, block_size_ << SECTOR_SHIFT);
b.mark_dirty();
}
void
block_cache::inc_hit_counter(unsigned flags)
{
if (flags & (GF_ZERO | GF_DIRTY))
write_hits_++;
else
read_hits_++;
}
void
block_cache::inc_miss_counter(unsigned flags)
{
if (flags & (GF_ZERO | GF_DIRTY))
write_misses_++;
else
read_misses_++;
}
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block_cache::block *
block_cache::lookup_or_read_block(block_address index, unsigned flags,
validator::ptr v)
{
auto it = block_set_.find(index, cmp_index());
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if (it != block_set_.end()) {
if (it->test_flags(BF_IO_PENDING)) {
inc_miss_counter(flags);
wait_specific(*it);
} else
inc_hit_counter(flags);
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if (flags & GF_ZERO)
zero_block(*it);
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else {
if (it->v_.get() != v.get()) {
if (it->test_flags(BF_DIRTY))
it->v_->prepare(it->data_, it->index_);
v->check(it->data_, it->index_);
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}
}
it->v_ = v;
return &(*it);
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} else {
inc_miss_counter(flags);
block *b = new_block(index);
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if (b) {
if (flags & GF_ZERO)
zero_block(*b);
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else {
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issue_read(*b);
wait_specific(*b);
v->check(b->data_, b->index_);
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}
b->v_ = v;
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}
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return (!b || b->error_) ? NULL : b;
}
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}
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block_cache::block &
block_cache::get(block_address index, unsigned flags, validator::ptr v)
{
check_index(index);
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block *b = lookup_or_read_block(index, flags, v);
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if (b) {
if (b->ref_count_ && (flags & (GF_DIRTY | GF_ZERO))) {
std::ostringstream out;
out << "attempt to write lock block " << index << " concurrently";
throw std::runtime_error(out.str());
}
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// FIXME: this gets called even for new blocks
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hit(*b);
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if (!b->ref_count_)
nr_locked_++;
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b->ref_count_++;
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if (flags & GF_BARRIER)
b->set_flags(BF_FLUSH);
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if (flags & GF_DIRTY)
b->set_flags(BF_DIRTY);
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return *b;
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}
std::ostringstream out;
out << "couldn't get block " << index;
throw std::runtime_error(out.str());
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}
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void
block_cache::preemptive_writeback()
{
unsigned nr_available = nr_cache_blocks_ - (dirty_.size() - io_pending_.size());
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if (nr_available < (WRITEBACK_LOW_THRESHOLD_PERCENT * nr_cache_blocks_ / 100))
writeback((WRITEBACK_HIGH_THRESHOLD_PERCENT * nr_cache_blocks_ / 100) - nr_available);
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}
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void
block_cache::release(block_cache::block &b)
{
assert(!b.ref_count_);
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nr_locked_--;
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if (b.test_flags(BF_FLUSH))
flush();
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if (b.test_flags(BF_DIRTY)) {
if (!b.test_flags(BF_PREVIOUSLY_DIRTY)) {
b.unlink();
dirty_.push_back(b);
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b.set_flags(BF_PREVIOUSLY_DIRTY);
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}
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if (b.test_flags(BF_FLUSH))
flush();
else
preemptive_writeback();
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b.clear_flags(BF_FLUSH);
}
}
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int
block_cache::flush()
{
while (!dirty_.empty()) {
block &b = dirty_.front();
if (b.ref_count_ || b.test_flags(BF_IO_PENDING))
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// The superblock may well be still locked.
continue;
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issue_write(b);
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}
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wait_all();
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return errored_.empty() ? 0 : -EIO;
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}
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void
block_cache::prefetch(block_address index)
{
check_index(index);
auto it = block_set_.find(index, cmp_index());
if (it == block_set_.end()) {
prefetches_++;
block *b = new_block(index);
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if (b)
issue_read(*b);
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}
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}
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void
block_cache::check_index(block_address index) const
{
if (index >= nr_data_blocks_) {
std::ostringstream out;
out << "block out of bounds ("
<< index << " >= " << nr_data_blocks_ << ")\n";
throw std::runtime_error(out.str());
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}
}
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//----------------------------------------------------------------