feat(server): acrtive memory defrag high level flow

Signed-off-by: Boaz Sade <boaz@dragonflydb.io>

src/core/compact_object_test.cc

@@ -3,9 +3,9 @@
 //
 #include "core/compact_object.h"
 
+#include <absl/strings/str_cat.h>
 #include <mimalloc.h>
 #include <xxhash.h>
-#include <absl/strings/str_cat.h>
 
 #include "base/gtest.h"
 #include "base/logging.h"
@@ -34,6 +34,36 @@ void PrintTo(const CompactObj& cobj, std::ostream* os) {
   *os << "cobj: [" << cobj.ObjType() << "]";
 }
 
+// This is for the mimalloc test - being able to find an address in memory
+// where we have memory underutilzation
+// see issue number 448 (https://github.com/dragonflydb/dragonfly/issues/448)
+std::vector<void*> AllocateForTest(int size, std::size_t allocate_size, int factor1 = 1,
+                                   int factor2 = 1) {
+  std::vector<void*> ptrs;
+  for (int index = 0; index < size; index++) {
+    auto alloc_size = index % 13 == 0 ? allocate_size * factor1 : allocate_size * factor2;
+    auto heap_alloc = mi_heap_get_backing();
+    void* ptr = mi_heap_malloc(heap_alloc, alloc_size);
+    ptrs.push_back(ptr);
+  }
+  return ptrs;
+}
+
+bool FindUnderutilizedMemory(const std::vector<void*>& ptrs, float ratio) {
+  auto it = std::find_if(ptrs.begin(), ptrs.end(), [&](auto p) {
+    int r = p && zmalloc_page_is_underutilized(p, ratio);
+    return r > 0;
+  });
+  return it != ptrs.end();
+}
+
+void DecimateMemory(std::vector<void*>* ptrs, size_t steps) {
+  for (size_t i = 24; i < ptrs->size(); i += steps) {
+    mi_free(ptrs->at(i));
+    ptrs->at(i) = nullptr;
+  }
+}
+
 class CompactObjectTest : public ::testing::Test {
  protected:
   static void SetUpTestSuite() {
@@ -110,7 +140,6 @@ TEST_F(CompactObjectTest, InlineAsciiEncoded) {
   EXPECT_EQ(s.size(), obj.Size());
 }
 
-
 TEST_F(CompactObjectTest, Int) {
   cobj_.SetString("0");
   EXPECT_EQ(0, cobj_.TryGetInt());
@@ -211,13 +240,13 @@ TEST_F(CompactObjectTest, FlatSet) {
   size_t allocated2, resident2, active2;
 
   zmalloc_get_allocator_info(&allocated1, &active1, &resident1);
-  dict *d = dictCreate(&setDictType);
+  dict* d = dictCreate(&setDictType);
   constexpr size_t kTestSize = 2000;
 
   for (size_t i = 0; i < kTestSize; ++i) {
     sds key = sdsnew("key:000000000000");
     key = sdscatfmt(key, "%U", i);
-    dictEntry *de = dictAddRaw(d, key,NULL);
+    dictEntry* de = dictAddRaw(d, key, NULL);
     de->v.val = NULL;
   }
 
@@ -259,4 +288,66 @@ TEST_F(CompactObjectTest, StreamObj) {
   EXPECT_FALSE(cobj_.IsInline());
 }
 
+TEST_F(CompactObjectTest, MimallocUnderutilzation) {
+  // We are testing with the same object size allocation here
+  // This test is for https://github.com/dragonflydb/dragonfly/issues/448
+  size_t allocation_size = 94;
+  int count = 2000;
+  std::vector<void*> ptrs = AllocateForTest(count, allocation_size);
+  bool found = FindUnderutilizedMemory(ptrs, 1.0f);
+  ASSERT_FALSE(found);
+  DecimateMemory(&ptrs, 26);
+  found = FindUnderutilizedMemory(ptrs, 1.0f);
+  ASSERT_TRUE(found);
+  for (auto* ptr : ptrs) {
+    mi_free(ptr);
+  }
+}
+
+TEST_F(CompactObjectTest, MimallocUnderutilzationDifferentSizes) {
+  // This test uses different objects sizes to cover more use cases
+  // related to issue https://github.com/dragonflydb/dragonfly/issues/448
+  size_t allocation_size = 97;
+  int count = 2000;
+  int mem_factor_1 = 3;
+  int mem_factor_2 = 2;
+  std::vector<void*> ptrs = AllocateForTest(count, allocation_size, mem_factor_1, mem_factor_2);
+  bool found = FindUnderutilizedMemory(ptrs, 1.0f);
+  ASSERT_FALSE(found);
+  DecimateMemory(&ptrs, 26);
+  found = FindUnderutilizedMemory(ptrs, 1.0f);
+  ASSERT_TRUE(found);
+  for (auto* ptr : ptrs) {
+    mi_free(ptr);
+  }
+}
+
+TEST_F(CompactObjectTest, MimallocUnderutilzationWithRealloc) {
+  // This test is checking underutilzation with reallocation as well as deallocation
+  // of the memory - see issue https://github.com/dragonflydb/dragonfly/issues/448
+  size_t allocation_size = 102;
+  int count = 2000;
+  int mem_factor_1 = 4;
+  int mem_factor_2 = 1;
+  std::vector<void*> ptrs = AllocateForTest(count, allocation_size, mem_factor_1, mem_factor_2);
+  bool found = FindUnderutilizedMemory(ptrs, 1.0f);
+  ASSERT_FALSE(found);
+  DecimateMemory(&ptrs, 26);
+  // TestMiMallocUnderutilized(ptrs, run_reallocation, allocation_size);
+  //  This is another case, where we are filling the "gaps" by doing re-allocations
+  //  in this case, since we are not setting all the values back it should still have
+  //  places that are not used. Plus since we are not looking at the first page
+  //  other pages should be underutilized.
+  for (size_t i = 24; i < ptrs.size(); i += 26) {
+    if (!ptrs[i]) {
+      ptrs[i] = mi_heap_malloc(mi_heap_get_backing(), allocation_size);
+    }
+  }
+  found = FindUnderutilizedMemory(ptrs, 1.0f);
+  ASSERT_TRUE(found);
+  for (auto* ptr : ptrs) {
+    mi_free(ptr);
+  }
+}
+
 }  // namespace dfly

src/redis/zmalloc.h

@@ -111,6 +111,12 @@ size_t zmalloc_get_smap_bytes_by_field(char *field, long pid);
 size_t zmalloc_get_memory_size(void);
 size_t zmalloc_usable_size(const void* p);
 
+/*
+ * checks whether a page that the pointer ptr located at is underutilized.
+ * This uses the current local thread heap.
+ * return 0 if not, 1 if underutilized
+ */
+int zmalloc_page_is_underutilized(void *ptr, float ratio);
 // roman: void zlibc_free(void *ptr);
 
 void init_zmalloc_threadlocal(void* heap);

src/redis/zmalloc_mi.c

@@ -137,3 +137,7 @@ void init_zmalloc_threadlocal(void* heap) {
     return;
   zmalloc_heap = heap;
 }
+
+int zmalloc_page_is_underutilized(void* ptr, float ratio) {
+  return mi_heap_page_is_underutilized(zmalloc_heap, ptr, ratio);
+}

src/server/CMakeLists.txt

@@ -7,7 +7,7 @@ if (CMAKE_SYSTEM_PROCESSOR STREQUAL "x86_64" AND CMAKE_BUILD_TYPE STREQUAL "Rele
   set_source_files_properties(dfly_main.cc PROPERTIES COMPILE_FLAGS -march=core2 COMPILE_DEFINITIONS SOURCE_PATH_FROM_BUILD_ENV=${CMAKE_SOURCE_DIR})
 endif()
 
-add_library(dfly_transaction db_slice.cc engine_shard_set.cc blocking_controller.cc common.cc
+add_library(dfly_transaction db_slice.cc malloc_stats.cc engine_shard_set.cc blocking_controller.cc common.cc
             io_mgr.cc journal/journal.cc journal/journal_slice.cc table.cc
             tiered_storage.cc transaction.cc)
 cxx_link(dfly_transaction uring_fiber_lib dfly_core strings_lib)

src/server/dragonfly_test.cc

@@ -50,6 +50,13 @@ class DflyEngineTest : public BaseFamilyTest {
   }
 };
 
+class DefragDflyEngineTest : public DflyEngineTest {
+ protected:
+  DefragDflyEngineTest() : DflyEngineTest() {
+    num_threads_ = 1;
+  }
+};
+
 // TODO: to implement equivalent parsing in redis parser.
 TEST_F(DflyEngineTest, Sds) {
   int argc;
@@ -749,6 +756,27 @@ TEST_F(DflyEngineTest, Bug496) {
   });
 }
 
+TEST_F(DefragDflyEngineTest, TestDefragOption) {
+  // Fill data into dragonfly and then check if we have
+  // any location in memory to defrag. See issue #448 for details about this.
+  EXPECT_GE(max_memory_limit, 100'000);
+  const int NUMBER_OF_KEYS = 184000;
+
+  RespExpr resp = Run({"DEBUG", "POPULATE", std::to_string(NUMBER_OF_KEYS), "key-name", "130"});
+  ASSERT_EQ(resp, "OK");
+  resp = Run({"DBSIZE"});
+  EXPECT_THAT(resp, IntArg(NUMBER_OF_KEYS));
+
+  shard_set->pool()->AwaitFiberOnAll([&](unsigned index, ProactorBase* base) {
+    EngineShard* shard = EngineShard::tlocal();
+    ASSERT_FALSE(shard == nullptr);  // we only have one and its should not be empty!
+    EXPECT_EQ(shard->GetDefragStats().success_count, 0);
+    // should not run at all!!
+    EXPECT_EQ(shard->GetDefragStats().tries, 0);
+    EXPECT_GT(GetMallocCurrentCommitted(), NUMBER_OF_KEYS);
+  });
+}
+
 // 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/engine_shard_set.cc

@@ -30,6 +30,18 @@ ABSL_FLAG(bool, cache_mode, false,
           "If true, the backend behaves like a cache, "
           "by evicting entries when getting close to maxmemory limit");
 
+// memory defragmented related flags
+ABSL_FLAG(float, mem_defrag_threshold,
+          1,  // The default now is to disable the task from running! change this to 0.05!!
+          "Minimum percentage of used memory relative to total available memory before running "
+          "defragmentation");
+
+ABSL_FLAG(float, commit_use_threshold, 1.3,
+          "The threshold to apply memory fragmentation between commited and used memory");
+
+ABSL_FLAG(float, mem_utilization_threshold, 0.8,
+          "memory page under utilization threshold. Ratio between used and commited size, above "
+          "this, memory in this page will defragmented");
 namespace dfly {
 
 using namespace util;
@@ -39,6 +51,8 @@ using absl::GetFlag;
 
 namespace {
 
+constexpr DbIndex DEFAULT_DB_INDEX = 0;
+
 vector<EngineShardSet::CachedStats> cached_stats;  // initialized in EngineShardSet::Init
 
 }  // namespace
@@ -56,6 +70,66 @@ EngineShard::Stats& EngineShard::Stats::operator+=(const EngineShard::Stats& o)
   return *this;
 }
 
+// This function checks 3 things:
+// 1. Don't try memory fragmentation if we don't use "enough" memory (control by
+// mem_defrag_threshold flag)
+// 2. That we had change in memory usage - to prevent endless loop - out of scope for now
+// 3. in case the above is OK, make sure that we have a "gap" between usage and commited memory
+// (control by commit_use_threshold flag)
+bool EngineShard::DefragTaskState::IsRequired() {
+  const double threshold_mem = max_memory_limit * GetFlag(FLAGS_mem_defrag_threshold);
+  const double commit_use_threshold = GetFlag(FLAGS_commit_use_threshold);
+
+  if (cursor > 0) {
+    return true;
+  }
+
+  uint64_t commited = GetMallocCurrentCommitted();
+  uint64_t mem_in_use = used_mem_current.load(memory_order_relaxed);
+
+  // we want to make sure that we are not running this to many times - i.e.
+  // if there was no change to the memory, don't run this
+  if (threshold_mem < commited && mem_in_use != 0 &&
+      (uint64_t(mem_in_use * commit_use_threshold) < commited)) {
+    // we have way more commited then actual usage
+    return true;
+  }
+
+  return false;
+}
+
+// for now this does nothing
+bool EngineShard::DoDefrag() {
+  // TODO - Impl!!
+  return defrag_state_.cursor > 0;
+}
+
+void EngineShard::DefragTaskState::Init() {
+  cursor = 0u;
+}
+
+// the memory defragmentation task is as follow:
+//  1. Check if memory usage is high enough
+//  2. Check if diff between commited and used memory is high enough
+//  3. Check if we have memory changes (to ensure that we not running endlessly). - TODO
+//  4. if all the above pass -> run on the shard and try to defragmented memory by re-allocating
+//  values
+//     if the cursor for this is signal that we are not done, schedule the task to run at high
+//     priority otherwise lower the task priority so that it would not use the CPU when not required
+uint32_t EngineShard::DefragTask() {
+  const auto shard_id = db_slice().shard_id();
+  bool required_state = defrag_state_.IsRequired();
+  if (required_state) {
+    VLOG(1) << shard_id << ": need to run defrag memory cursor state: " << defrag_state_.cursor;
+    if (DoDefrag()) {
+      // we didn't finish the scan
+      return util::ProactorBase::kOnIdleMaxLevel;
+    }
+  }
+  // by default we just want to not get in the way..
+  return 0u;
+}
+
 EngineShard::EngineShard(util::ProactorBase* pb, bool update_db_time, mi_heap_t* heap)
     : queue_(kQueueLen), txq_([](const Transaction* t) { return t->txid(); }), mi_resource_(heap),
       db_slice_(pb->GetIndex(), GetFlag(FLAGS_cache_mode), this) {
@@ -75,6 +149,9 @@ EngineShard::EngineShard(util::ProactorBase* pb, bool update_db_time, mi_heap_t*
   tmp_str1 = sdsempty();
 
   db_slice_.UpdateExpireBase(absl::GetCurrentTimeNanos() / 1000000, 0);
+  // start the defragmented task here
+  defrag_state_.Init();
+  defrag_task_ = pb->AddOnIdleTask([this]() { return this->DefragTask(); });
 }
 
 EngineShard::~EngineShard() {
@@ -92,6 +169,10 @@ void EngineShard::Shutdown() {
   if (periodic_task_) {
     ProactorBase::me()->CancelPeriodic(periodic_task_);
   }
+
+  if (defrag_task_ != 0) {
+    ProactorBase::me()->RemoveOnIdleTask(defrag_task_);
+  }
 }
 
 void EngineShard::InitThreadLocal(ProactorBase* pb, bool update_db_time) {

src/server/engine_shard_set.h

@@ -41,6 +41,11 @@ class EngineShard {
     Stats& operator+=(const Stats&);
   };
 
+  struct DefragStats {
+    uint64_t success_count = 0;  // how many objects were moved
+    uint64_t tries = 0;          // how many times we tried
+  };
+
   // EngineShard() is private down below.
   ~EngineShard();
 
@@ -141,9 +146,25 @@ class EngineShard {
     journal_ = j;
   }
 
+  const DefragStats& GetDefragStats() const {
+    return defrag_state_.stats;
+  }
+
   void TEST_EnableHeartbeat();
 
  private:
+  struct DefragTaskState {
+    // we will add more data members later
+    uint64_t cursor = 0u;
+    DefragStats stats;
+
+    void Init();
+
+    // check the current threshold and return true if
+    // we need to do the de-fermentation
+    bool IsRequired();
+  };
+
   EngineShard(util::ProactorBase* pb, bool update_db_time, mi_heap_t* heap);
 
   // blocks the calling fiber.
@@ -153,6 +174,23 @@ class EngineShard {
 
   void CacheStats();
 
+  // We are running a task that checks whether we need to
+  // do memory de-fragmentation here, this task only run
+  // when there are available CPU time.
+  // --------------------------------------------------------------------------
+  // NOTE: This task is running with exclusive access to the shard.
+  // i.e. - Since we are using shared noting access here, and all access
+  // are done using fibers, This fiber is run only when no other fiber in the
+  // context of the controlling thread will access this shard!
+  // --------------------------------------------------------------------------
+  uint32_t DefragTask();
+
+  // scan the shard with the cursor and apply
+  // de-fragmentation option for entries. This function will return the new cursor at the end of the
+  // scan This function is called from context of StartDefragTask
+  // return true if we did not complete the shard scan
+  bool DoDefrag();
+
   ::util::fibers_ext::FiberQueue queue_;
   ::boost::fibers::fiber fiber_q_;
 
@@ -170,6 +208,8 @@ class EngineShard {
   IntentLock shard_lock_;
 
   uint32_t periodic_task_ = 0;
+  uint32_t defrag_task_ = 0;
+  DefragTaskState defrag_state_;
   std::unique_ptr<TieredStorage> tiered_storage_;
   std::unique_ptr<BlockingController> blocking_controller_;