Simplified distributed block storage with strong consistency, like in Ceph
You can not select more than 25 topics Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
 
 
 
 
 
 

298 lines
10 KiB

#include "blockstore.h"
journal_flusher_t::journal_flusher_t(int flusher_count, blockstore *bs)
{
this->bs = bs;
this->flusher_count = flusher_count;
this->active_flushers = 0;
this->active_until_sync = 0;
this->sync_required = true;
this->sync_threshold = flusher_count == 1 ? 1 : flusher_count/2;
co = new journal_flusher_co[flusher_count];
for (int i = 0; i < flusher_count; i++)
{
co[i].bs = bs;
co[i].flusher = this;
}
}
journal_flusher_co::journal_flusher_co()
{
wait_state = 0;
simple_callback = [this](ring_data_t* data)
{
if (data->res < 0)
{
throw new std::runtime_error("write operation failed. in-memory state is corrupted. AAAAAAAaaaaaaaaa!!!111");
}
wait_count--;
};
}
journal_flusher_t::~journal_flusher_t()
{
delete[] co;
}
void journal_flusher_t::loop()
{
if (!active_flushers && !flush_queue.size())
{
return;
}
for (int i = 0; i < flusher_count; i++)
{
co[i].loop();
}
}
#define await_sqe(label) \
resume_##label:\
sqe = bs->get_sqe();\
if (!sqe)\
{\
wait_state = label;\
return;\
}\
data = ((ring_data_t*)sqe->user_data);
void journal_flusher_co::loop()
{
// This is much better than implementing the whole function as an FSM
// Maybe I should consider a coroutine library like https://github.com/hnes/libaco ...
if (wait_state == 1)
goto resume_1;
else if (wait_state == 2)
goto resume_2;
else if (wait_state == 3)
goto resume_3;
else if (wait_state == 4)
goto resume_4;
else if (wait_state == 5)
goto resume_5;
else if (wait_state == 6)
goto resume_6;
else if (wait_state == 7)
goto resume_7;
else if (wait_state == 8)
goto resume_8;
else if (wait_state == 9)
goto resume_9;
else if (wait_state == 10)
goto resume_10;
else if (wait_state == 11)
goto resume_11;
resume_0:
if (!flusher->flush_queue.size())
return;
cur = flusher->flush_queue.front();
flusher->flush_queue.pop_front();
dirty_it = bs->dirty_db.find(cur);
if (dirty_it != bs->dirty_db.end())
{
flusher->active_flushers++;
flusher->active_until_sync++;
v.clear();
wait_count = 0;
clean_loc = UINT64_MAX;
skip_copy = false;
do
{
if (dirty_it->second.state == ST_J_STABLE)
{
// First we submit all reads
offset = dirty_it->second.offset;
len = dirty_it->second.len;
it = v.begin();
while (1)
{
for (; it != v.end(); it++)
if (it->offset >= offset)
break;
if (it == v.end() || it->offset > offset)
{
submit_len = it->offset >= offset+len ? len : it->offset-offset;
await_sqe(1);
v.insert(it, (copy_buffer_t){ .offset = offset, .len = submit_len, .buf = memalign(512, submit_len) });
data->iov = (struct iovec){ v.back().buf, (size_t)submit_len };
data->callback = simple_callback;
io_uring_prep_readv(
sqe, bs->journal.fd, &data->iov, 1, bs->journal.offset + dirty_it->second.location + offset
);
wait_count++;
}
if (it == v.end() || it->offset+it->len >= offset+len)
{
break;
}
}
// So subsequent stabilizers don't flush the entry again
dirty_it->second.state = ST_J_MOVE_READ_SUBMITTED;
}
else if (dirty_it->second.state == ST_D_STABLE)
{
// Copy last STABLE entry metadata
if (!skip_copy)
{
clean_loc = dirty_it->second.location;
}
skip_copy = true;
}
else if (IS_STABLE(dirty_it->second.state))
{
break;
}
dirty_it--;
} while (dirty_it != bs->dirty_db.begin() && dirty_it->first.oid == cur.oid);
if (clean_loc == UINT64_MAX)
{
// Find it in clean_db
auto clean_it = bs->clean_db.find(cur.oid);
if (clean_it == bs->clean_db.end())
{
// Object not present at all. This is a bug.
throw new std::runtime_error("BUG: Object we are trying to flush not allocated on the data device");
}
else
clean_loc = clean_it->second.location;
}
// Also we need to submit the metadata read. We do a read-modify-write for every operation.
// But we must check if the same sector is already in memory.
// Another option is to keep all raw metadata in memory all the time. Maybe I'll do it sometime...
// And yet another option is to use LSM trees for metadata, but it sophisticates everything a lot,
// so I'll avoid it as long as I can.
meta_sector = (clean_loc / (512 / sizeof(clean_disk_entry))) * 512;
meta_pos = (clean_loc % (512 / sizeof(clean_disk_entry)));
meta_it = flusher->meta_sectors.find(meta_sector);
if (meta_it == flusher->meta_sectors.end())
{
// Not in memory yet, read it
meta_it = flusher->meta_sectors.emplace(meta_sector, (meta_sector_t){
.offset = meta_sector,
.len = 512,
.state = 0, // 0 = not read yet
.buf = memalign(512, 512),
.usage_count = 1,
}).first;
await_sqe(2);
data->iov = (struct iovec){ meta_it->second.buf, 512 };
data->callback = [this](ring_data_t* data)
{
if (data->res < 0)
{
throw new std::runtime_error("write operation failed. in-memory state is corrupted. AAAAAAAaaaaaaaaa!!!111");
}
meta_it->second.state = 1;
wait_count--;
};
io_uring_prep_writev(
sqe, bs->meta_fd, &data->iov, 1, bs->meta_offset + meta_sector
);
wait_count++;
}
else
meta_it->second.usage_count++;
wait_state = 3;
resume_3:
if (wait_count > 0)
return;
// Reads completed, submit writes
for (it = v.begin(); it != v.end(); it++)
{
await_sqe(4);
data->iov = (struct iovec){ it->buf, (size_t)it->len };
data->callback = simple_callback;
io_uring_prep_writev(
sqe, bs->data_fd, &data->iov, 1, bs->data_offset + clean_loc + it->offset
);
wait_count++;
}
// And a metadata write
resume_5:
if (meta_it->second.state == 0)
{
// metadata sector is still being read, wait for it
wait_state = 5;
return;
}
*((clean_disk_entry*)meta_it->second.buf + meta_pos) = {
.oid = cur.oid,
.version = cur.version,
};
// I consider unordered writes to data & metadata safe here, because
// "dirty" entries always override "clean" entries in our case
await_sqe(6);
data->iov = (struct iovec){ meta_it->second.buf, 512 };
data->callback = simple_callback;
io_uring_prep_writev(
sqe, bs->meta_fd, &data->iov, 1, bs->meta_offset + meta_sector
);
wait_count++;
wait_state = 7;
resume_7:
if (wait_count > 0)
return;
// Done, free all buffers
meta_it->second.usage_count--;
if (meta_it->second.usage_count == 0)
{
free(meta_it->second.buf);
flusher->meta_sectors.erase(meta_it);
}
for (it = v.begin(); it != v.end(); it++)
{
free(it->buf);
}
v.clear();
flusher->active_until_sync--;
if (flusher->sync_required)
{
// And sync everything (in batches - not per each operation!)
cur_sync = flusher->syncs.end();
if (cur_sync == flusher->syncs.begin())
cur_sync = flusher->syncs.emplace(flusher->syncs.end(), (flusher_sync_t){ .ready_count = 0, .state = 0 });
else
cur_sync--;
cur_sync->ready_count++;
if (cur_sync->ready_count >= flusher->sync_threshold ||
!flusher->active_until_sync && !flusher->flush_queue.size())
{
// Sync batch is ready. Do it.
await_sqe(9);
data->callback = simple_callback;
io_uring_prep_fsync(sqe, bs->data_fd, 0);
wait_count++;
if (bs->meta_fd != bs->data_fd)
{
await_sqe(10);
data->callback = simple_callback;
io_uring_prep_fsync(sqe, bs->meta_fd, 0);
wait_count++;
}
wait_state = 11;
resume_11:
if (wait_count > 0)
return;
// Sync completed. All previous coroutines waiting for it must be resumed
cur_sync->state = 1;
}
// Wait until someone else sends and completes a sync.
resume_8:
if (!cur_sync->state)
{
wait_state = 8;
return;
}
cur_sync->ready_count--;
if (cur_sync->ready_count == 0)
{
flusher->syncs.erase(cur_sync);
}
}
// FIXME: Adjust clean_db and dirty_db
// FIXME: ...and clear part of the journal
wait_state = 0;
flusher->active_flushers--;
goto resume_0;
}
}