Make flusher_count adaptive and limit write iodepth

src/blockstore_flush.cpp

@@ -7,6 +7,8 @@ journal_flusher_t::journal_flusher_t(int flusher_count, blockstore_impl_t *bs)
 {
     this->bs = bs;
     this->flusher_count = flusher_count;
+    this->cur_flusher_count = 1;
+    this->target_flusher_count = 1;
     dequeuing = false;
     trimming = false;
     active_flushers = 0;
@@ -68,10 +70,24 @@ bool journal_flusher_t::is_active()
 
 void journal_flusher_t::loop()
 {
-    for (int i = 0; (active_flushers > 0 || dequeuing) && i < flusher_count; i++)
+    target_flusher_count = bs->write_iodepth*2;
+    if (target_flusher_count <= 0)
+        target_flusher_count = 1;
+    else if (target_flusher_count > flusher_count)
+        target_flusher_count = flusher_count;
+    if (target_flusher_count > cur_flusher_count)
+        cur_flusher_count = target_flusher_count;
+    else if (target_flusher_count < cur_flusher_count)
     {
-        co[i].loop();
+        while (target_flusher_count < cur_flusher_count)
+        {
+            if (co[cur_flusher_count-1].wait_state)
+                break;
+            cur_flusher_count--;
+        }
     }
+    for (int i = 0; (active_flushers > 0 || dequeuing) && i < cur_flusher_count; i++)
+        co[i].loop();
 }
 
 void journal_flusher_t::enqueue_flush(obj_ver_id ov)

src/blockstore_flush.h

@@ -80,7 +80,7 @@ class journal_flusher_t
 {
     int trim_wanted = 0;
     bool dequeuing;
-    int flusher_count;
+    int flusher_count, cur_flusher_count, target_flusher_count;
     int flusher_start_threshold;
     journal_flusher_co *co;
     blockstore_impl_t *bs;

src/blockstore_impl.h

@@ -199,7 +199,10 @@ class blockstore_impl_t
     // Suitable only for server SSDs with capacitors, requires disabled data and journal fsyncs
     int immediate_commit = IMMEDIATE_NONE;
     bool inmemory_meta = false;
-    int flusher_count;
+    // Maximum flusher count
+    unsigned flusher_count;
+    // Maximum queue depth
+    unsigned max_write_iodepth = 128;
     /******* END OF OPTIONS *******/
 
     struct ring_consumer_t ring_consumer;
@@ -226,6 +229,7 @@ class blockstore_impl_t
 
     struct journal_t journal;
     journal_flusher_t *flusher;
+    int write_iodepth = 0;
 
     bool live = false, queue_stall = false;
     ring_loop_t *ringloop;

src/blockstore_open.cpp

@@ -70,6 +70,7 @@ void blockstore_impl_t::parse_config(blockstore_config_t & config)
     meta_block_size = strtoull(config["meta_block_size"].c_str(), NULL, 10);
     bitmap_granularity = strtoull(config["bitmap_granularity"].c_str(), NULL, 10);
     flusher_count = strtoull(config["flusher_count"].c_str(), NULL, 10);
+    max_write_iodepth = strtoull(config["max_write_iodepth"].c_str(), NULL, 10);
     // Validate
     if (!block_size)
     {
@@ -83,6 +84,10 @@ void blockstore_impl_t::parse_config(blockstore_config_t & config)
     {
         flusher_count = 32;
     }
+    if (!max_write_iodepth)
+    {
+        max_write_iodepth = 128;
+    }
     if (!disk_alignment)
     {
         disk_alignment = 4096;

src/blockstore_write.cpp

@@ -167,6 +167,10 @@ int blockstore_impl_t::dequeue_write(blockstore_op_t *op)
             .version = op->version,
         }, e).first;
     }
+    if (write_iodepth >= max_write_iodepth)
+    {
+        return 0;
+    }
     if ((dirty_it->second.state & BS_ST_TYPE_MASK) == BS_ST_BIG_WRITE)
     {
         blockstore_journal_check_t space_check(this);
@@ -191,6 +195,7 @@ int blockstore_impl_t::dequeue_write(blockstore_op_t *op)
             FINISH_OP(op);
             return 1;
         }
+        write_iodepth++;
         BS_SUBMIT_GET_SQE(sqe, data);
         dirty_it->second.location = loc << block_order;
         dirty_it->second.state = (dirty_it->second.state & ~BS_ST_WORKFLOW_MASK) | BS_ST_SUBMITTED;
@@ -243,6 +248,7 @@ int blockstore_impl_t::dequeue_write(blockstore_op_t *op)
         {
             return 0;
         }
+        write_iodepth++;
         // There is sufficient space. Get SQE(s)
         struct io_uring_sqe *sqe1 = NULL;
         if (immediate_commit != IMMEDIATE_NONE ||
@@ -432,6 +438,7 @@ resume_4:
     }
     // Acknowledge write
     op->retval = op->len;
+    write_iodepth--;
     FINISH_OP(op);
     return 1;
 }