feat(server): Implement MEMORY MALLOC-STATS command (#363)

Signed-off-by: Roman Gershman <roman@dragonflydb.io>

Signed-off-by: Roman Gershman <roman@dragonflydb.io>

src/server/memory_cmd.cc

@@ -0,0 +1,68 @@
+// Copyright 2022, DragonflyDB authors.  All rights reserved.
+// See LICENSE for licensing terms.
+//
+
+#include "server/memory_cmd.h"
+
+#include <absl/strings/str_cat.h>
+#include <mimalloc.h>
+
+#include "facade/error.h"
+#include "server/server_state.h"
+
+using namespace std;
+using namespace facade;
+
+namespace dfly {
+
+namespace {
+
+void MiStatsCallback(const char* msg, void* arg) {
+  string* str = (string*)arg;
+  absl::StrAppend(str, msg);
+}
+
+bool MiArenaVisit(const mi_heap_t* heap, const mi_heap_area_t* area, void* block, size_t block_size,
+                  void* arg) {
+  string* str = (string*)arg;
+
+  absl::StrAppend(str, "block_size ", block_size, ", reserved ",
+                  area->reserved, ", comitted ", area->committed,
+                  ", used: ", area->used * block_size, "\n");
+
+  return true;
+};
+
+}  // namespace
+
+MemoryCmd::MemoryCmd(ServerFamily* owner, ConnectionContext* cntx) : sf_(*owner), cntx_(cntx) {
+}
+
+void MemoryCmd::Run(CmdArgList args) {
+  string_view sub_cmd = ArgS(args, 1);
+  if (sub_cmd == "USAGE") {
+    // dummy output, in practice not implemented yet.
+    return (*cntx_)->SendLong(1);
+  } else if (sub_cmd == "MALLOC-STATS") {
+    return MallocStats();
+  }
+
+  string err = UnknownSubCmd(sub_cmd, "MEMORY");
+  return (*cntx_)->SendError(err, kSyntaxErrType);
+}
+
+void MemoryCmd::MallocStats() {
+  string str;
+  absl::StrAppend(&str, "___ Begin mimalloc statistics ___\n");
+  mi_stats_print_out(MiStatsCallback, &str);
+
+  absl::StrAppend(&str, "\nArena statistics from a single thread:\n");
+  mi_heap_t* data_heap = ServerState::tlocal()->data_heap();
+  mi_heap_visit_blocks(data_heap, false /* visit all blocks*/, MiArenaVisit, &str);
+
+  absl::StrAppend(&str, "--- End mimalloc statistics ---\n");
+
+  return (*cntx_)->SendBulkString(str);
+}
+
+}  // namespace dfly