chore: allow slow and precise memory measurement of an object

Specifically fixes "MEMORY USAGE" for lists.

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

src/core/compact_object.cc

@@ -46,9 +46,15 @@ constexpr XXH64_hash_t kHashSeed = 24061983;
 constexpr size_t kAlignSize = 8u;
 
 // Approximation since does not account for listpacks.
-size_t QlMAllocSize(quicklist* ql) {
-  size_t res = ql->len * sizeof(quicklistNode) + znallocx(sizeof(quicklist));
-  return res + ql->count * 16;  // we account for each member 16 bytes.
+size_t QlMAllocSize(quicklist* ql, bool slow) {
+  size_t node_size = ql->len * sizeof(quicklistNode) + znallocx(sizeof(quicklist));
+  if (slow) {
+    for (quicklistNode* node = ql->head; node; node = node->next) {
+      node_size += zmalloc_usable_size(node->entry);
+    }
+    return node_size;
+  }
+  return node_size + ql->count * 16;  // we account for each member 16 bytes.
 }
 
 inline void FreeObjSet(unsigned encoding, void* ptr, MemoryResource* mr) {
@@ -291,7 +297,7 @@ static_assert(sizeof(CompactObj) == 18);
 
 namespace detail {
 
-size_t RobjWrapper::MallocUsed() const {
+size_t RobjWrapper::MallocUsed(bool slow) const {
   if (!inner_obj_)
     return 0;
 
@@ -301,8 +307,8 @@ size_t RobjWrapper::MallocUsed() const {
       return InnerObjMallocUsed();
     case OBJ_LIST:
       if (encoding_ == OBJ_ENCODING_QUICKLIST)
-        return QlMAllocSize((quicklist*)inner_obj_);
-      return ((QList*)inner_obj_)->MallocUsed();
+        return QlMAllocSize((quicklist*)inner_obj_, slow);
+      return ((QList*)inner_obj_)->MallocUsed(slow);
     case OBJ_SET:
       return MallocUsedSet(encoding_, inner_obj_);
     case OBJ_HASH:
@@ -1132,12 +1138,12 @@ void CompactObj::Free() {
   memset(u_.inline_str, 0, kInlineLen);
 }
 
-size_t CompactObj::MallocUsed() const {
+size_t CompactObj::MallocUsed(bool slow) const {
   if (!HasAllocated())
     return 0;
 
   if (taglen_ == ROBJ_TAG) {
-    return u_.r_obj.MallocUsed();
+    return u_.r_obj.MallocUsed(slow);
   }
 
   if (taglen_ == JSON_TAG) {

src/core/compact_object.h

@@ -37,7 +37,7 @@ class RobjWrapper {
   RobjWrapper() : sz_(0), type_(0), encoding_(0) {
   }
 
-  size_t MallocUsed() const;
+  size_t MallocUsed(bool slow) const;
 
   uint64_t HashCode() const;
   bool Equal(const RobjWrapper& ow) const;
@@ -359,9 +359,9 @@ class CompactObj {
   // Postcondition: The object is an in-memory string.
   void Materialize(std::string_view str, bool is_raw);
 
-  // In case this object a single blob, returns number of bytes allocated on heap
-  // for that blob. Otherwise returns 0.
-  size_t MallocUsed() const;
+  // Returns the approximation of memory used by the object.
+  // If slow is true, may use more expensive methods to calculate the precise size.
+  size_t MallocUsed(bool slow = false) const;
 
   // Resets the object to empty state (string).
   void Reset();

src/core/qlist.cc

@@ -431,10 +431,17 @@ bool QList::Replace(long index, std::string_view elem) {
   return false;
 }
 
-size_t QList::MallocUsed() const {
+size_t QList::MallocUsed(bool slow) const {
   // Approximation since does not account for listpacks.
-  size_t res = len_ * sizeof(quicklistNode) + znallocx(sizeof(quicklist));
-  return res + count_ * 16;  // we account for each member 16 bytes.
+  size_t node_size = len_ * sizeof(quicklistNode) + znallocx(sizeof(quicklist));
+  if (slow) {
+    for (quicklistNode* node = head_; node; node = node->next) {
+      node_size += zmalloc_usable_size(node->entry);
+    }
+    return node_size;
+  }
+
+  return node_size + count_ * 16;  // we account for each member 16 bytes.
 }
 
 void QList::Iterate(IterateFunc cb, long start, long end) const {

src/core/qlist.h

@@ -103,7 +103,7 @@ class QList {
   // Returns true if item was replaced, false if index is out of range.
   bool Replace(long index, std::string_view elem);
 
-  size_t MallocUsed() const;
+  size_t MallocUsed(bool slow) const;
 
   void Iterate(IterateFunc cb, long start, long end) const;
 

src/server/dfly_main.cc

@@ -799,5 +799,9 @@ Usage: dragonfly [FLAGS]
     unlink(pidfile_path.c_str());
   }
 
+  // Returns memory to OS.
+  // This is a workaround for a bug in mi_malloc that may cause a crash on exit.
+  mi_collect(true);
+
   return res;
 }

src/server/dragonfly_test.cc

@@ -768,6 +768,21 @@ TEST_F(DflyEngineTest, EvalBug2664) {
   EXPECT_THAT(resp, DoubleArg(42.9));
 }
 
+TEST_F(DflyEngineTest, MemoryUsage) {
+  for (unsigned i = 0; i < 1000; ++i) {
+    Run({"rpush", "l1", StrCat("val", i)});
+  }
+
+  for (unsigned i = 0; i < 1000; ++i) {
+    Run({"rpush", "l2", StrCat(string('a', 200), i)});
+  }
+  auto resp = Run({"memory", "usage", "l1"});
+  EXPECT_GT(*resp.GetInt(), 8000);
+
+  resp = Run({"memory", "usage", "l2"});
+  EXPECT_GT(*resp.GetInt(), 100000);
+}
+
 // TODO: to test transactions with a single shard since then all transactions become local.
 // To consider having a parameter in dragonfly engine controlling number of shards
 // unconditionally from number of cpus. TO TEST BLPOP under multi for single/multi argument case.

src/server/memory_cmd.cc

@@ -83,7 +83,8 @@ std::string MallocStatsCb(bool backing, unsigned tid) {
 }
 
 size_t MemoryUsage(PrimeIterator it) {
-  return it->first.MallocUsed() + it->second.MallocUsed();
+  size_t key_size = it->first.MallocUsed();
+  return key_size + it->second.MallocUsed(true);
 }
 
 }  // namespace