feat: Add eviction based on rss memory

Signed-off-by: Stepan Bagritsevich <stefan@dragonflydb.io>

src/server/dfly_main.cc

@@ -819,7 +819,12 @@ Usage: dragonfly [FLAGS]
   // export MIMALLOC_VERBOSE=1 to see the options before the override.
   mi_option_enable(mi_option_show_errors);
   mi_option_set(mi_option_max_warnings, 0);
+
   mi_option_enable(mi_option_purge_decommits);
+  DCHECK(mi_option_get(mi_option_reset_decommits) == 1);
+
+  mi_option_set(mi_option_purge_delay, 0);
+  DCHECK(!mi_option_get(mi_option_reset_delay));
 
   fb2::SetDefaultStackResource(&fb2::std_malloc_resource, kFiberDefaultStackSize);
 

src/server/engine_shard.cc

@@ -19,10 +19,12 @@ extern "C" {
 #include "server/search/doc_index.h"
 #include "server/server_state.h"
 #include "server/tiered_storage.h"
+#include "server/tiering/common.h"
 #include "server/transaction.h"
 #include "util/fibers/proactor_base.h"
 
 using namespace std;
+using namespace ::dfly::tiering::literals;
 
 ABSL_FLAG(float, mem_defrag_threshold, 0.7,
           "Minimum percentage of used memory relative to maxmemory cap before running "
@@ -65,6 +67,9 @@ ABSL_FLAG(double, eviction_memory_budget_threshold, 0.1,
           "Eviction starts when the free memory (including RSS memory) drops below "
           "eviction_memory_budget_threshold * max_memory_limit.");
 
+ABSL_FLAG(uint64_t, force_decommit_threshold, 8_MB,
+          "The threshold of memory to force decommit when memory is under pressure.");
+
 ABSL_DECLARE_FLAG(uint32_t, max_eviction_per_heartbeat);
 
 namespace dfly {
@@ -216,45 +221,6 @@ size_t CalculateHowManyBytesToEvictOnShard(size_t global_memory_limit, size_t gl
   return shard_budget < shard_memory_threshold ? (shard_memory_threshold - shard_budget) : 0;
 }
 
-/* Calculates the number of bytes to evict based on memory and rss memory usage. */
-size_t CalculateEvictionBytes() {
-  const size_t shards_count = shard_set->size();
-  const double eviction_memory_budget_threshold = GetFlag(FLAGS_eviction_memory_budget_threshold);
-
-  const size_t shard_memory_budget_threshold =
-      size_t(max_memory_limit * eviction_memory_budget_threshold) / shards_count;
-
-  const size_t global_used_memory = used_mem_current.load(memory_order_relaxed);
-
-  // Calculate how many bytes we need to evict on this shard
-  size_t goal_bytes = CalculateHowManyBytesToEvictOnShard(max_memory_limit, global_used_memory,
-                                                          shard_memory_budget_threshold);
-
-  // TODO: Eviction due to rss usage is not working well as it causes eviction
-  // of to many keys untill we finally see decrease in rss. We need to improve
-  // this logic before we enable it.
-  /*
-  const double rss_oom_deny_ratio = ServerState::tlocal()->rss_oom_deny_ratio;
-  // If rss_oom_deny_ratio is set, we should evict depending on rss memory too
-  if (rss_oom_deny_ratio > 0.0) {
-    const size_t max_rss_memory = size_t(rss_oom_deny_ratio * max_memory_limit);
-    // We start eviction when we have less than eviction_memory_budget_threshold * 100% of free rss
-    memory const size_t shard_rss_memory_budget_threshold =
-        size_t(max_rss_memory * eviction_memory_budget_threshold) / shards_count;
-
-    // Calculate how much rss memory is used by all shards
-    const size_t global_used_rss_memory = rss_mem_current.load(memory_order_relaxed);
-
-    // Try to evict more bytes if we are close to the rss memory limit
-    goal_bytes = std::max(
-        goal_bytes, CalculateHowManyBytesToEvictOnShard(max_rss_memory, global_used_rss_memory,
-                                                        shard_rss_memory_budget_threshold));
-  }
-  */
-
-  return goal_bytes;
-}
-
 }  // namespace
 
 __thread EngineShard* EngineShard::shard_ = nullptr;
@@ -358,6 +324,18 @@ bool EngineShard::DefragTaskState::CheckRequired() {
     return false;
   }
 
+  std::optional<ShardMemUsage> shard_mem_usage;
+
+  if (GetFlag(FLAGS_enable_heartbeat_eviction)) {
+    shard_mem_usage = ReadShardMemUsage(GetFlag(FLAGS_mem_defrag_page_utilization_threshold));
+    const static double eviction_waste_threshold = 0.05;
+    if (shard_mem_usage->wasted_mem >
+        (uint64_t(shard_mem_usage->commited * eviction_waste_threshold))) {
+      VLOG(1) << "memory issue found for memory " << shard_mem_usage.value();
+      return true;
+    }
+  }
+
   const std::size_t global_threshold = max_memory_limit * GetFlag(FLAGS_mem_defrag_threshold);
   if (global_threshold > rss_mem_current.load(memory_order_relaxed)) {
     return false;
@@ -372,11 +350,15 @@ bool EngineShard::DefragTaskState::CheckRequired() {
   }
   last_check_time = now;
 
-  ShardMemUsage usage = ReadShardMemUsage(GetFlag(FLAGS_mem_defrag_page_utilization_threshold));
+  if (!shard_mem_usage) {
+    shard_mem_usage = ReadShardMemUsage(GetFlag(FLAGS_mem_defrag_page_utilization_threshold));
+  }
+
+  DCHECK(shard_mem_usage.has_value());
 
   const double waste_threshold = GetFlag(FLAGS_mem_defrag_waste_threshold);
-  if (usage.wasted_mem > (uint64_t(usage.commited * waste_threshold))) {
+  if (shard_mem_usage->wasted_mem > (uint64_t(shard_mem_usage->commited * waste_threshold))) {
-    VLOG(1) << "memory issue found for memory " << usage;
+    VLOG(1) << "memory issue found for memory " << shard_mem_usage.value();
     return true;
   }
 
@@ -811,6 +793,7 @@ void EngineShard::RetireExpiredAndEvict() {
   DbContext db_cntx;
   db_cntx.time_now_ms = GetCurrentTimeMs();
 
+  size_t deleted_bytes = 0;
   size_t eviction_goal = GetFlag(FLAGS_enable_heartbeat_eviction) ? CalculateEvictionBytes() : 0;
 
   for (unsigned i = 0; i < db_slice.db_array_size(); ++i) {
@@ -822,6 +805,7 @@ void EngineShard::RetireExpiredAndEvict() {
     if (expt->size() > 0) {
       DbSlice::DeleteExpiredStats stats = db_slice.DeleteExpiredStep(db_cntx, ttl_delete_target);
 
+      deleted_bytes += stats.deleted_bytes;
       eviction_goal -= std::min(eviction_goal, size_t(stats.deleted_bytes));
       counter_[TTL_TRAVERSE].IncBy(stats.traversed);
       counter_[TTL_DELETE].IncBy(stats.deleted);
@@ -843,9 +827,75 @@ void EngineShard::RetireExpiredAndEvict() {
                << " bytes. Max eviction per heartbeat: "
                << GetFlag(FLAGS_max_eviction_per_heartbeat);
 
+      deleted_bytes += evicted_bytes;
       eviction_goal -= std::min(eviction_goal, evicted_bytes);
     }
   }
+
+  auto& deleted_bytes_before_decommit = eviction_state_.deleted_bytes_before_decommit;
+  eviction_state_.deleted_bytes_before_rss_update += deleted_bytes;
+  deleted_bytes_before_decommit += deleted_bytes;
+
+  if (deleted_bytes_before_decommit >= absl::GetFlag(FLAGS_force_decommit_threshold)) {
+    // Decommit with force
+    deleted_bytes_before_decommit = 0;
+    ServerState::tlocal()->DecommitMemory(ServerState::kAllMemory);
+  }
+}
+
+size_t EngineShard::CalculateEvictionBytes() {
+  const size_t shards_count = shard_set->size();
+  const double eviction_memory_budget_threshold = GetFlag(FLAGS_eviction_memory_budget_threshold);
+
+  const size_t shard_memory_budget_threshold =
+      size_t(max_memory_limit * eviction_memory_budget_threshold) / shards_count;
+
+  const size_t global_used_memory = used_mem_current.load(memory_order_relaxed);
+
+  // Calculate how many bytes we need to evict on this shard
+  size_t goal_bytes = CalculateHowManyBytesToEvictOnShard(max_memory_limit, global_used_memory,
+                                                          shard_memory_budget_threshold);
+
+  LOG_IF_EVERY_N(INFO, goal_bytes > 0, 10)
+      << "Memory goal bytes: " << goal_bytes << ", used memory: " << global_used_memory
+      << ", memory limit: " << max_memory_limit;
+
+  // If rss_oom_deny_ratio is set, we should evict depending on rss memory too
+  const double rss_oom_deny_ratio = ServerState::tlocal()->rss_oom_deny_ratio;
+  if (rss_oom_deny_ratio > 0.0) {
+    const size_t max_rss_memory = size_t(rss_oom_deny_ratio * max_memory_limit);
+    /* We start eviction when we have less than eviction_memory_budget_threshold * 100% of free rss
+     * memory */
+    const size_t shard_rss_memory_budget_threshold =
+        size_t(max_rss_memory * eviction_memory_budget_threshold) / shards_count;
+
+    // Calculate how much rss memory is used by all shards
+    const size_t global_used_rss_memory = rss_mem_current.load(memory_order_relaxed);
+
+    auto& global_rss_memory_at_prev_eviction = eviction_state_.global_rss_memory_at_prev_eviction;
+    auto& deleted_bytes_before_rss_update = eviction_state_.deleted_bytes_before_rss_update;
+    if (global_used_rss_memory < eviction_state_.global_rss_memory_at_prev_eviction) {
+      deleted_bytes_before_rss_update -=
+          std::min(deleted_bytes_before_rss_update,
+                   (global_rss_memory_at_prev_eviction - global_used_rss_memory) / shards_count);
+    }
+
+    global_rss_memory_at_prev_eviction = global_used_rss_memory;
+
+    // Try to evict more bytes if we are close to the rss memory limit
+    const size_t rss_goal_bytes = CalculateHowManyBytesToEvictOnShard(
+        max_rss_memory, global_used_rss_memory - deleted_bytes_before_rss_update * shards_count,
+        shard_rss_memory_budget_threshold);
+
+    LOG_IF_EVERY_N(INFO, goal_bytes > 0, 10)
+        << "Rss memory goal bytes: " << rss_goal_bytes
+        << ", rss used memory: " << global_used_rss_memory
+        << ", rss memory limit: " << max_rss_memory
+        << ", deleted_bytes_before_rss_update: " << deleted_bytes_before_rss_update;
+
+    goal_bytes = std::max(goal_bytes, rss_goal_bytes);
+  }
+  return goal_bytes;
 }
 
 void EngineShard::CacheStats() {

src/server/engine_shard.h

@@ -216,6 +216,12 @@ class EngineShard {
     void ResetScanState();
   };
 
+  struct EvictionTaskState {
+    size_t deleted_bytes_before_decommit = 0;
+    size_t deleted_bytes_before_rss_update = 0;
+    size_t global_rss_memory_at_prev_eviction = 0;
+  };
+
   EngineShard(util::ProactorBase* pb, mi_heap_t* heap);
 
   // blocks the calling fiber.
@@ -227,6 +233,9 @@ class EngineShard {
   void Heartbeat();
   void RetireExpiredAndEvict();
 
+  /* Calculates the number of bytes to evict based on memory and rss memory usage. */
+  size_t CalculateEvictionBytes();
+
   void CacheStats();
 
   // We are running a task that checks whether we need to
@@ -267,6 +276,7 @@ class EngineShard {
   IntentLock shard_lock_;
 
   uint32_t defrag_task_ = 0;
+  EvictionTaskState eviction_state_;  // Used on eviction fiber
   util::fb2::Fiber fiber_heartbeat_periodic_;
   util::fb2::Done fiber_heartbeat_periodic_done_;
 

tests/dragonfly/memory_test.py

@@ -6,6 +6,15 @@ from . import dfly_args
 from .instance import DflyInstance, DflyInstanceFactory
 
 
+def extract_fragmentation_waste(memory_arena):
+    """
+    Extracts the fragmentation waste from the memory arena info.
+    """
+    match = re.search(r"fragmentation waste:\s*([0-9.]+)%", memory_arena)
+    assert match.group(1) is not None
+    return float(match.group(1))
+
+
 @pytest.mark.slow
 @pytest.mark.opt_only
 @pytest.mark.parametrize(
@@ -176,49 +185,101 @@ async def test_eval_with_oom(df_factory: DflyInstanceFactory):
     assert rss_before_eval * 1.01 > info["used_memory_rss"]
 
 
-@pytest.mark.skip("rss eviction disabled")
 @pytest.mark.asyncio
-@dfly_args(
+@pytest.mark.parametrize(
-    {
+    "proactor_threads_param, maxmemory_param",
-        "proactor_threads": 1,
+    [(1, 512 * (1024**2)), (1, 6 * (1024**3)), (4, 6 * (1024**3))],
-        "cache_mode": "true",
-        "maxmemory": "5gb",
-        "rss_oom_deny_ratio": 0.8,
-        "max_eviction_per_heartbeat": 100,
-    }
 )
-async def test_cache_eviction_with_rss_deny_oom(
+async def test_cache_eviction_with_rss_deny_oom_simple_case(
-    async_client: aioredis.Redis,
+    df_factory: DflyInstanceFactory,
+    proactor_threads_param,
+    maxmemory_param,
 ):
     """
     Test to verify that cache eviction is triggered even if used memory is small but rss memory is above limit
     """
+    df_server = df_factory.create(
+        proactor_threads=proactor_threads_param,
+        cache_mode="true",
+        maxmemory=maxmemory_param,
+        rss_oom_deny_ratio=0.8,
+    )
+    df_server.start()
 
-    max_memory = 5 * 1024 * 1024 * 1024  # 5G
+    async_client = df_server.client()
-    rss_max_memory = int(max_memory * 0.8)
 
-    data_fill_size = int(0.9 * rss_max_memory)  # 95% of rss_max_memory
+    max_memory = maxmemory_param
+    rss_oom_deny_ratio = 0.8
+    eviction_memory_budget_threshold = 0.1  # 10% of max_memory
+
+    data_fill_size = int((rss_oom_deny_ratio + 0.05) * max_memory)  # 85% of max_memory
 
     val_size = 1024 * 5  # 5 kb
     num_keys = data_fill_size // val_size
 
     await async_client.execute_command("DEBUG", "POPULATE", num_keys, "key", val_size)
-    # Test that used memory is less than 90% of max memory
+
+    # Test that used memory is less than 90% of max memory to not to start eviction based on used_memory
     memory_info = await async_client.info("memory")
     assert (
         memory_info["used_memory"] < max_memory * 0.9
-    ), "Used memory should be less than 90% of max memory."
+    ), "Used memory should be less than 90% of max memory to not to start eviction based on used_memory."
     assert (
-        memory_info["used_memory_rss"] > rss_max_memory * 0.9
+        memory_info["used_memory_rss"] > max_memory * rss_oom_deny_ratio
-    ), "RSS memory should be less than 90% of rss max memory (max_memory * rss_oom_deny_ratio)."
+    ), "Used RSS memory should be more than 80% of rss max memory (max_memory * rss_oom_deny_ratio) to start eviction based on rss memory usage."
 
-    # Get RSS memory after creating new connections
+    # Track eviction stats
     memory_info = await async_client.info("memory")
-    while memory_info["used_memory_rss"] > rss_max_memory * 0.9:
+    prev_evicted_keys = 0
+    evicted_keys_repeat_count = 0
+    while True:
+        # Wait for some time
         await asyncio.sleep(1)
+
         memory_info = await async_client.info("memory")
         logging.info(
-            f'Current rss: {memory_info["used_memory_rss"]}. rss eviction threshold: {rss_max_memory * 0.9}.'
+            f'Current used memory: {memory_info["used_memory"]}, current used rss: {memory_info["used_memory_rss"]}, rss eviction threshold: {max_memory * (rss_oom_deny_ratio - eviction_memory_budget_threshold)}.'
         )
+
         stats_info = await async_client.info("stats")
         logging.info(f'Current evicted: {stats_info["evicted_keys"]}. Total keys: {num_keys}.')
+
+        # Check if evicted keys are not increasing
+        if prev_evicted_keys == stats_info["evicted_keys"]:
+            evicted_keys_repeat_count += 1
+        else:
+            prev_evicted_keys = stats_info["evicted_keys"]
+            evicted_keys_repeat_count = 1
+
+        if evicted_keys_repeat_count > 2:
+            break
+
+    # Wait for some time
+    await asyncio.sleep(2)
+
+    memory_arena = await async_client.execute_command("MEMORY", "ARENA")
+    fragmentation_waste = extract_fragmentation_waste(memory_arena)
+    logging.info(f"Memory fragmentation waste: {fragmentation_waste}")
+    assert fragmentation_waste < 12.0, "Memory fragmentation waste should be less than 12%."
+
+    # Assert that no more keys are evicted
+    memory_info = await async_client.info("memory")
+    stats_info = await async_client.info("stats")
+
+    assert memory_info["used_memory"] > max_memory * (
+        rss_oom_deny_ratio - eviction_memory_budget_threshold - 0.08
+    ), "We should not evict all items."
+    assert memory_info["used_memory"] < max_memory * (
+        rss_oom_deny_ratio - eviction_memory_budget_threshold
+    ), "Used memory should be smaller than threshold."
+    assert memory_info["used_memory_rss"] > max_memory * (
+        rss_oom_deny_ratio - eviction_memory_budget_threshold - 0.08
+    ), "We should not evict all items."
+
+    evicted_keys = stats_info["evicted_keys"]
+    # We may evict slightly more than prev_evicted_keys due to gaps in RSS memory usage
+    assert (
+        evicted_keys > 0
+        and evicted_keys >= prev_evicted_keys
+        and evicted_keys <= prev_evicted_keys * 1.0015
+    ), "We should not evict more items."