Merge pull request #24380 from vespa-engine/geirst/generation-holder-new-implv8.66.20

Implement GenerationHolder in terms of the generic generation hold list.

31 files changed, 131 insertions, 263 deletions

diff --git a/searchcore/src/tests/proton/documentmetastore/lid_allocator/lid_allocator_test.cpp b/searchcore/src/tests/proton/documentmetastore/lid_allocator/lid_allocator_test.cpp
index 2d675e82db2..157d10e6652 100644
--- a/searchcore/src/tests/proton/documentmetastore/lid_allocator/lid_allocator_test.cpp
+++ b/searchcore/src/tests/proton/documentmetastore/lid_allocator/lid_allocator_test.cpp
@@ -28,7 +28,7 @@ protected:
 
     ~LidAllocatorTest()
     {
-        _gen_hold.clearHoldLists();
+        _gen_hold.reclaim_all();
     }
 
     uint32_t get_size() { return _allocator.getActiveLids().size(); }
diff --git a/searchcore/src/tests/proton/documentmetastore/lid_state_vector/lid_state_vector_test.cpp b/searchcore/src/tests/proton/documentmetastore/lid_state_vector/lid_state_vector_test.cpp
index ab45cca0971..68958bbe3e4 100644
--- a/searchcore/src/tests/proton/documentmetastore/lid_state_vector/lid_state_vector_test.cpp
+++ b/searchcore/src/tests/proton/documentmetastore/lid_state_vector/lid_state_vector_test.cpp
@@ -22,7 +22,7 @@ protected:
 
     ~LidStateVectorTest()
     {
-        _gen_hold.clearHoldLists();
+        _gen_hold.reclaim_all();
     }
 
 };
diff --git a/searchcore/src/vespa/searchcore/proton/documentmetastore/documentmetastore.cpp b/searchcore/src/vespa/searchcore/proton/documentmetastore/documentmetastore.cpp
index b1b5f45a8fa..1853e939d42 100644
--- a/searchcore/src/vespa/searchcore/proton/documentmetastore/documentmetastore.cpp
+++ b/searchcore/src/vespa/searchcore/proton/documentmetastore/documentmetastore.cpp
@@ -224,7 +224,7 @@ DocumentMetaStore::onUpdateStat()
 {
     auto &compaction_strategy = getConfig().getCompactionStrategy();
     vespalib::MemoryUsage usage = _metaDataStore.getMemoryUsage();
-    usage.incAllocatedBytesOnHold(getGenerationHolder().getHeldBytes());
+    usage.incAllocatedBytesOnHold(getGenerationHolder().get_held_bytes());
     size_t bvSize = _lidAlloc.getUsedLidsSize();
     usage.incAllocatedBytes(bvSize);
     usage.incUsedBytes(bvSize);
@@ -245,7 +245,7 @@ DocumentMetaStore::onGenerationChange(generation_t generation)
 {
     _gidToLidMap.getAllocator().freeze();
     _gidToLidMap.getAllocator().transferHoldLists(generation - 1);
-    getGenerationHolder().transferHoldLists(generation - 1);
+    getGenerationHolder().assign_generation(generation - 1);
     updateStat(false);
 }
 
@@ -254,7 +254,7 @@ DocumentMetaStore::removeOldGenerations(generation_t firstUsed)
 {
     _gidToLidMap.getAllocator().trimHoldLists(firstUsed);
     _lidAlloc.trimHoldLists(firstUsed);
-    getGenerationHolder().trimHoldLists(firstUsed);
+    getGenerationHolder().reclaim(firstUsed);
 }
 
 std::unique_ptr<search::AttributeSaver>
@@ -442,7 +442,7 @@ DocumentMetaStore::~DocumentMetaStore()
     // TODO: Properly notify about modified buckets when using shared bucket db
     // between document types
     unload();
-    getGenerationHolder().clearHoldLists();
+    getGenerationHolder().reclaim_all();
     assert(get_shrink_lid_space_blockers() == 0);
 }
 
@@ -1009,7 +1009,7 @@ DocumentMetaStore::holdUnblockShrinkLidSpace()
 {
     assert(get_shrink_lid_space_blockers() > 0);
     auto hold = std::make_unique<ShrinkBlockHeld>(*this);
-    getGenerationHolder().hold(std::move(hold));
+    getGenerationHolder().insert(std::move(hold));
     incGeneration();
 }
 
diff --git a/searchlib/src/tests/common/bitvector/bitvector_test.cpp b/searchlib/src/tests/common/bitvector/bitvector_test.cpp
index 79af28d20be..7a26202682b 100644
--- a/searchlib/src/tests/common/bitvector/bitvector_test.cpp
+++ b/searchlib/src/tests/common/bitvector/bitvector_test.cpp
@@ -654,8 +654,8 @@ TEST("requireThatGrowWorks")
     EXPECT_EQUAL(4095u, v.writer().capacity());
     EXPECT_EQUAL(3u, v.writer().countTrueBits());
 
-    g.transferHoldLists(1);
-    g.trimHoldLists(2);
+    g.assign_generation(1);
+    g.reclaim(2);
 }
 
 TEST("require that growable bit vectors keeps memory allocator")
@@ -676,8 +676,8 @@ TEST("require that growable bit vectors keeps memory allocator")
     EXPECT_EQUAL(AllocStats(4, 1), stats);
     v.writer().resize(1); // DO NOT TRY THIS AT HOME
     EXPECT_EQUAL(AllocStats(5, 2), stats);
-    g.transferHoldLists(1);
-    g.trimHoldLists(2);
+    g.assign_generation(1);
+    g.reclaim(2);
 }
 
 TEST_MAIN() { TEST_RUN_ALL(); }
diff --git a/searchlib/src/tests/predicate/simple_index_test.cpp b/searchlib/src/tests/predicate/simple_index_test.cpp
index dfa8c12deec..7bf52680782 100644
--- a/searchlib/src/tests/predicate/simple_index_test.cpp
+++ b/searchlib/src/tests/predicate/simple_index_test.cpp
@@ -74,7 +74,7 @@ struct Fixture {
     Fixture() : _generation_holder(), _limit_provider(),
                 _index(_generation_holder, _limit_provider, config) {}
     ~Fixture() {
-        _generation_holder.clearHoldLists();
+        _generation_holder.reclaim_all();
     }
     SimpleIndex<MyData> &index() {
         return _index;
diff --git a/searchlib/src/vespa/searchlib/attribute/flagattribute.cpp b/searchlib/src/vespa/searchlib/attribute/flagattribute.cpp
index ef796d3f3d2..df75b0ab4e5 100644
--- a/searchlib/src/vespa/searchlib/attribute/flagattribute.cpp
+++ b/searchlib/src/vespa/searchlib/attribute/flagattribute.cpp
@@ -223,7 +223,7 @@ FlagAttributeT<B>::resizeBitVectors(uint32_t neededSize)
         }
     }
     _bitVectorSize = newSize;
-    _bitVectorHolder.transferHoldLists(this->getCurrentGeneration());
+    _bitVectorHolder.assign_generation(this->getCurrentGeneration());
 }
 
 
@@ -232,7 +232,7 @@ void
 FlagAttributeT<B>::removeOldGenerations(vespalib::GenerationHandler::generation_t firstUsed)
 {
     B::removeOldGenerations(firstUsed);
-    _bitVectorHolder.trimHoldLists(firstUsed);
+    _bitVectorHolder.reclaim(firstUsed);
 }
 
 template class FlagAttributeT<FlagBaseImpl>;
diff --git a/searchlib/src/vespa/searchlib/attribute/load_utils.hpp b/searchlib/src/vespa/searchlib/attribute/load_utils.hpp
index 62d645326ce..463a62ab01a 100644
--- a/searchlib/src/vespa/searchlib/attribute/load_utils.hpp
+++ b/searchlib/src/vespa/searchlib/attribute/load_utils.hpp
@@ -68,7 +68,7 @@ loadFromEnumeratedSingleValue(Vector &vector,
     using ValueType = typename Vector::ValueType;
     using NonAtomicValueType = atomic_utils::NonAtomicValue_t<ValueType>;
     uint32_t numDocs = attrReader.getEnumCount();
-    genHolder.clearHoldLists();
+    genHolder.reclaim_all();
     vector.reset();
     vector.unsafe_reserve(numDocs);
     for (uint32_t doc = 0; doc < numDocs; ++doc) {
diff --git a/searchlib/src/vespa/searchlib/attribute/predicate_attribute.cpp b/searchlib/src/vespa/searchlib/attribute/predicate_attribute.cpp
index c1897c71366..f2e07bba853 100644
--- a/searchlib/src/vespa/searchlib/attribute/predicate_attribute.cpp
+++ b/searchlib/src/vespa/searchlib/attribute/predicate_attribute.cpp
@@ -89,7 +89,7 @@ PredicateAttribute::PredicateAttribute(const vespalib::string &base_file_name, c
 
 PredicateAttribute::~PredicateAttribute()
 {
-    getGenerationHolder().clearHoldLists();
+    getGenerationHolder().reclaim_all();
 }
 
 void PredicateAttribute::populateIfNeeded() {
@@ -118,7 +118,7 @@ PredicateAttribute::onUpdateStat()
     combined.merge(_min_feature.getMemoryUsage());
     combined.merge(_interval_range_vector.getMemoryUsage());
     combined.merge(_index->getMemoryUsage());
-    combined.mergeGenerationHeldBytes(getGenerationHolder().getHeldBytes());
+    combined.mergeGenerationHeldBytes(getGenerationHolder().get_held_bytes());
     this->updateStatistics(_min_feature.size(), _min_feature.size(),
                            combined.allocatedBytes(), combined.usedBytes(),
                            combined.deadBytes(), combined.allocatedBytesOnHold());
@@ -127,14 +127,14 @@ PredicateAttribute::onUpdateStat()
 void
 PredicateAttribute::removeOldGenerations(generation_t firstUsed)
 {
-    getGenerationHolder().trimHoldLists(firstUsed);
+    getGenerationHolder().reclaim(firstUsed);
     _index->trimHoldLists(firstUsed);
 }
 
 void
 PredicateAttribute::onGenerationChange(generation_t generation)
 {
-    getGenerationHolder().transferHoldLists(generation - 1);
+    getGenerationHolder().assign_generation(generation - 1);
     _index->transferHoldLists(generation - 1);
 }
 
diff --git a/searchlib/src/vespa/searchlib/attribute/reference_attribute.cpp b/searchlib/src/vespa/searchlib/attribute/reference_attribute.cpp
index 0ebef4af8b0..36fb02f4c4b 100644
--- a/searchlib/src/vespa/searchlib/attribute/reference_attribute.cpp
+++ b/searchlib/src/vespa/searchlib/attribute/reference_attribute.cpp
@@ -165,7 +165,7 @@ ReferenceAttribute::removeOldGenerations(generation_t firstUsed)
 {
     _referenceMappings.trimHoldLists(firstUsed);
     _store.trimHoldLists(firstUsed);
-    getGenerationHolder().trimHoldLists(firstUsed);
+    getGenerationHolder().reclaim(firstUsed);
 }
 
 void
@@ -175,7 +175,7 @@ ReferenceAttribute::onGenerationChange(generation_t generation)
     _store.freeze();
     _referenceMappings.transferHoldLists(generation - 1);
     _store.transferHoldLists(generation - 1);
-    getGenerationHolder().transferHoldLists(generation - 1);
+    getGenerationHolder().assign_generation(generation - 1);
 }
 
 void
@@ -203,7 +203,7 @@ ReferenceAttribute::onUpdateStat()
     _compaction_spec = ReferenceAttributeCompactionSpec(compaction_strategy.should_compact_memory(total),
                                                         compaction_strategy.should_compact_memory(dictionary_memory_usage));
     total.merge(dictionary_memory_usage);
-    total.mergeGenerationHeldBytes(getGenerationHolder().getHeldBytes());
+    total.mergeGenerationHeldBytes(getGenerationHolder().get_held_bytes());
     total.merge(_indices.getMemoryUsage());
     total.merge(_referenceMappings.getMemoryUsage());
     updateStatistics(getTotalValueCount(), getUniqueValueCount(),
diff --git a/searchlib/src/vespa/searchlib/attribute/singleboolattribute.cpp b/searchlib/src/vespa/searchlib/attribute/singleboolattribute.cpp
index 7574508517d..6e07a9e658e 100644
--- a/searchlib/src/vespa/searchlib/attribute/singleboolattribute.cpp
+++ b/searchlib/src/vespa/searchlib/attribute/singleboolattribute.cpp
@@ -29,7 +29,7 @@ SingleBoolAttribute(const vespalib::string &baseFileName, const GrowStrategy & g
 
 SingleBoolAttribute::~SingleBoolAttribute()
 {
-    getGenerationHolder().clearHoldLists();
+    getGenerationHolder().reclaim_all();
 }
 
 void
@@ -95,7 +95,7 @@ SingleBoolAttribute::onUpdateStat() {
     vespalib::MemoryUsage usage;
     usage.setAllocatedBytes(_bv.writer().extraByteSize());
     usage.setUsedBytes(_bv.writer().sizeBytes());
-    usage.mergeGenerationHeldBytes(getGenerationHolder().getHeldBytes());
+    usage.mergeGenerationHeldBytes(getGenerationHolder().get_held_bytes());
     usage.merge(this->getChangeVectorMemoryUsage());
     this->updateStatistics(_bv.writer().size(), _bv.writer().size(), usage.allocatedBytes(), usage.usedBytes(),
                            usage.deadBytes(), usage.allocatedBytesOnHold());
@@ -191,7 +191,7 @@ SingleBoolAttribute::onLoad(vespalib::Executor *)
     bool ok(attrReader.hasData());
     if (ok) {
         setCreateSerialNum(attrReader.getCreateSerialNum());
-        getGenerationHolder().clearHoldLists();
+        getGenerationHolder().reclaim_all();
         _bv.writer().clear();
         uint32_t numDocs = attrReader.getNextData();
         _bv.extend(numDocs);
@@ -258,12 +258,12 @@ SingleBoolAttribute::getEstimatedSaveByteSize() const
 
 void
 SingleBoolAttribute::removeOldGenerations(generation_t firstUsed) {
-    getGenerationHolder().trimHoldLists(firstUsed);
+    getGenerationHolder().reclaim(firstUsed);
 }
 
 void
 SingleBoolAttribute::onGenerationChange(generation_t generation) {
-    getGenerationHolder().transferHoldLists(generation - 1);
+    getGenerationHolder().assign_generation(generation - 1);
 }
 
 }
diff --git a/searchlib/src/vespa/searchlib/attribute/singleenumattribute.hpp b/searchlib/src/vespa/searchlib/attribute/singleenumattribute.hpp
index c4abcfbc25a..11742bf8f48 100644
--- a/searchlib/src/vespa/searchlib/attribute/singleenumattribute.hpp
+++ b/searchlib/src/vespa/searchlib/attribute/singleenumattribute.hpp
@@ -25,7 +25,7 @@ SingleValueEnumAttribute(const vespalib::string &baseFileName,
 template <typename B>
 SingleValueEnumAttribute<B>::~SingleValueEnumAttribute()
 {
-    getGenerationHolder().clearHoldLists();
+    getGenerationHolder().reclaim_all();
 }
 
 template <typename B>
@@ -128,7 +128,7 @@ SingleValueEnumAttribute<B>::onUpdateStat()
     // update statistics
     vespalib::MemoryUsage total = _enumIndices.getMemoryUsage();
     auto& compaction_strategy = this->getConfig().getCompactionStrategy();
-    total.mergeGenerationHeldBytes(getGenerationHolder().getHeldBytes());
+    total.mergeGenerationHeldBytes(getGenerationHolder().get_held_bytes());
     total.merge(this->_enumStore.update_stat(compaction_strategy));
     total.merge(this->getChangeVectorMemoryUsage());
     mergeMemoryStats(total);
@@ -218,7 +218,7 @@ SingleValueEnumAttribute<B>::fillValues(LoadedVector & loaded)
 {
     if constexpr (!std::is_same_v<LoadedVector, NoLoadedVector>) {
         uint32_t numDocs = this->getNumDocs();
-        getGenerationHolder().clearHoldLists();
+        getGenerationHolder().reclaim_all();
         _enumIndices.reset();
         _enumIndices.unsafe_reserve(numDocs);
         for (DocId doc = 0; doc < numDocs; ++doc, loaded.next()) {
@@ -267,7 +267,7 @@ void
 SingleValueEnumAttribute<B>::removeOldGenerations(generation_t firstUsed)
 {
     this->_enumStore.trim_hold_lists(firstUsed);
-    getGenerationHolder().trimHoldLists(firstUsed);
+    getGenerationHolder().reclaim(firstUsed);
 }
 
 template <typename B>
@@ -281,7 +281,7 @@ SingleValueEnumAttribute<B>::onGenerationChange(generation_t generation)
      * sufficiently new frozen tree.
      */
     freezeEnumDictionary();
-    getGenerationHolder().transferHoldLists(generation - 1);
+    getGenerationHolder().assign_generation(generation - 1);
     this->_enumStore.transfer_hold_lists(generation - 1);
 }
 
diff --git a/searchlib/src/vespa/searchlib/attribute/singlenumericattribute.hpp b/searchlib/src/vespa/searchlib/attribute/singlenumericattribute.hpp
index b9c1c3686de..bbacc10e79c 100644
--- a/searchlib/src/vespa/searchlib/attribute/singlenumericattribute.hpp
+++ b/searchlib/src/vespa/searchlib/attribute/singlenumericattribute.hpp
@@ -32,7 +32,7 @@ SingleValueNumericAttribute(const vespalib::string & baseFileName, const Attribu
 template <typename B>
 SingleValueNumericAttribute<B>::~SingleValueNumericAttribute()
 {
-    getGenerationHolder().clearHoldLists();
+    getGenerationHolder().reclaim_all();
 }
 
 template <typename B>
@@ -65,7 +65,7 @@ void
 SingleValueNumericAttribute<B>::onUpdateStat()
 {
     vespalib::MemoryUsage usage = _data.getMemoryUsage();
-    usage.mergeGenerationHeldBytes(getGenerationHolder().getHeldBytes());
+    usage.mergeGenerationHeldBytes(getGenerationHolder().get_held_bytes());
     usage.merge(this->getChangeVectorMemoryUsage());
     this->updateStatistics(_data.size(), _data.size(),
                            usage.allocatedBytes(), usage.usedBytes(), usage.deadBytes(), usage.allocatedBytesOnHold());
@@ -97,14 +97,14 @@ template <typename B>
 void
 SingleValueNumericAttribute<B>::removeOldGenerations(generation_t firstUsed)
 {
-    getGenerationHolder().trimHoldLists(firstUsed);
+    getGenerationHolder().reclaim(firstUsed);
 }
 
 template <typename B>
 void
 SingleValueNumericAttribute<B>::onGenerationChange(generation_t generation)
 {
-    getGenerationHolder().transferHoldLists(generation - 1);
+    getGenerationHolder().assign_generation(generation - 1);
 }
 
 template <typename B>
@@ -143,7 +143,7 @@ SingleValueNumericAttribute<B>::onLoad(vespalib::Executor *)
         return onLoadEnumerated(attrReader);
     
     const size_t sz(attrReader.getDataCount());
-    getGenerationHolder().clearHoldLists();
+    getGenerationHolder().reclaim_all();
     _data.reset();
     _data.unsafe_reserve(sz);
     for (uint32_t i = 0; i < sz; ++i) {
diff --git a/searchlib/src/vespa/searchlib/attribute/singlesmallnumericattribute.cpp b/searchlib/src/vespa/searchlib/attribute/singlesmallnumericattribute.cpp
index b69ed017b52..02ab5798f9f 100644
--- a/searchlib/src/vespa/searchlib/attribute/singlesmallnumericattribute.cpp
+++ b/searchlib/src/vespa/searchlib/attribute/singlesmallnumericattribute.cpp
@@ -36,7 +36,7 @@ SingleValueSmallNumericAttribute(const vespalib::string & baseFileName,
 
 SingleValueSmallNumericAttribute::~SingleValueSmallNumericAttribute()
 {
-    getGenerationHolder().clearHoldLists();
+    getGenerationHolder().reclaim_all();
 }
 
 void
@@ -97,7 +97,7 @@ void
 SingleValueSmallNumericAttribute::onUpdateStat()
 {
     vespalib::MemoryUsage usage = _wordData.getMemoryUsage();
-    usage.mergeGenerationHeldBytes(getGenerationHolder().getHeldBytes());
+    usage.mergeGenerationHeldBytes(getGenerationHolder().get_held_bytes());
     uint32_t numDocs = B::getNumDocs();
     updateStatistics(numDocs, numDocs,
                      usage.allocatedBytes(), usage.usedBytes(),
@@ -108,14 +108,14 @@ SingleValueSmallNumericAttribute::onUpdateStat()
 void
 SingleValueSmallNumericAttribute::removeOldGenerations(generation_t firstUsed)
 {
-    getGenerationHolder().trimHoldLists(firstUsed);
+    getGenerationHolder().reclaim(firstUsed);
 }
 
 
 void
 SingleValueSmallNumericAttribute::onGenerationChange(generation_t generation)
 {
-    getGenerationHolder().transferHoldLists(generation - 1);
+    getGenerationHolder().assign_generation(generation - 1);
 }
 
 
@@ -127,7 +127,7 @@ SingleValueSmallNumericAttribute::onLoad(vespalib::Executor *)
     if (ok) {
         setCreateSerialNum(attrReader.getCreateSerialNum());
         const size_t sz(attrReader.getDataCount());
-        getGenerationHolder().clearHoldLists();
+        getGenerationHolder().reclaim_all();
         _wordData.reset();
         _wordData.unsafe_reserve(sz - 1);
         Word numDocs = attrReader.getNextData();
diff --git a/searchlib/src/vespa/searchlib/common/growablebitvector.cpp b/searchlib/src/vespa/searchlib/common/growablebitvector.cpp
index e3334be3fd9..5f971e21cd3 100644
--- a/searchlib/src/vespa/searchlib/common/growablebitvector.cpp
+++ b/searchlib/src/vespa/searchlib/common/growablebitvector.cpp
@@ -72,7 +72,7 @@ bool
 GrowableBitVector::hold(GenerationHeldBase::UP v)
 {
     if (v) {
-        _generationHolder.hold(std::move(v));
+        _generationHolder.insert(std::move(v));
         return true;
     }
     return false;
diff --git a/searchlib/src/vespa/searchlib/tensor/dense_tensor_attribute.cpp b/searchlib/src/vespa/searchlib/tensor/dense_tensor_attribute.cpp
index 636c949be08..0c797fa7fe1 100644
--- a/searchlib/src/vespa/searchlib/tensor/dense_tensor_attribute.cpp
+++ b/searchlib/src/vespa/searchlib/tensor/dense_tensor_attribute.cpp
@@ -172,7 +172,7 @@ DenseTensorAttribute::DenseTensorAttribute(vespalib::stringref baseFileName, con
 
 DenseTensorAttribute::~DenseTensorAttribute()
 {
-    getGenerationHolder().clearHoldLists();
+    getGenerationHolder().reclaim_all();
     _tensorStore.clearHoldLists();
 }
 
diff --git a/searchlib/src/vespa/searchlib/tensor/direct_tensor_attribute.cpp b/searchlib/src/vespa/searchlib/tensor/direct_tensor_attribute.cpp
index d9fe025b4e5..a68f7fcc3da 100644
--- a/searchlib/src/vespa/searchlib/tensor/direct_tensor_attribute.cpp
+++ b/searchlib/src/vespa/searchlib/tensor/direct_tensor_attribute.cpp
@@ -15,7 +15,7 @@ DirectTensorAttribute::DirectTensorAttribute(stringref name, const Config &cfg)
 
 DirectTensorAttribute::~DirectTensorAttribute()
 {
-    getGenerationHolder().clearHoldLists();
+    getGenerationHolder().reclaim_all();
     _tensorStore.clearHoldLists();
 }
 
diff --git a/searchlib/src/vespa/searchlib/tensor/serialized_fast_value_attribute.cpp b/searchlib/src/vespa/searchlib/tensor/serialized_fast_value_attribute.cpp
index 52ccb4c91b1..d2153ac93ad 100644
--- a/searchlib/src/vespa/searchlib/tensor/serialized_fast_value_attribute.cpp
+++ b/searchlib/src/vespa/searchlib/tensor/serialized_fast_value_attribute.cpp
@@ -23,7 +23,7 @@ SerializedFastValueAttribute::SerializedFastValueAttribute(stringref name, const
 
 SerializedFastValueAttribute::~SerializedFastValueAttribute()
 {
-    getGenerationHolder().clearHoldLists();
+    getGenerationHolder().reclaim_all();
     _tensorStore.clearHoldLists();
 }
 
diff --git a/searchlib/src/vespa/searchlib/tensor/tensor_attribute.cpp b/searchlib/src/vespa/searchlib/tensor/tensor_attribute.cpp
index 99a30b59bd1..b233960e339 100644
--- a/searchlib/src/vespa/searchlib/tensor/tensor_attribute.cpp
+++ b/searchlib/src/vespa/searchlib/tensor/tensor_attribute.cpp
@@ -113,13 +113,13 @@ void
 TensorAttribute::removeOldGenerations(generation_t firstUsed)
 {
     _tensorStore.trimHoldLists(firstUsed);
-    getGenerationHolder().trimHoldLists(firstUsed);
+    getGenerationHolder().reclaim(firstUsed);
 }
 
 void
 TensorAttribute::onGenerationChange(generation_t generation)
 {
-    getGenerationHolder().transferHoldLists(generation - 1);
+    getGenerationHolder().assign_generation(generation - 1);
     _tensorStore.transferHoldLists(generation - 1);
 }
 
@@ -169,7 +169,7 @@ TensorAttribute::update_stat()
 {
     vespalib::MemoryUsage result = _refVector.getMemoryUsage();
     result.merge(_tensorStore.update_stat(getConfig().getCompactionStrategy()));
-    result.mergeGenerationHeldBytes(getGenerationHolder().getHeldBytes());
+    result.mergeGenerationHeldBytes(getGenerationHolder().get_held_bytes());
     return result;
 }
 
@@ -178,7 +178,7 @@ TensorAttribute::memory_usage() const
 {
     vespalib::MemoryUsage result = _refVector.getMemoryUsage();
     result.merge(_tensorStore.getMemoryUsage());
-    result.mergeGenerationHeldBytes(getGenerationHolder().getHeldBytes());
+    result.mergeGenerationHeldBytes(getGenerationHolder().get_held_bytes());
     return result;
 }
 
diff --git a/vespalib/CMakeLists.txt b/vespalib/CMakeLists.txt
index 532ec870ce9..8edd7fb2c5d 100644
--- a/vespalib/CMakeLists.txt
+++ b/vespalib/CMakeLists.txt
@@ -182,7 +182,6 @@ vespa_define_module(
     src/tests/util/cgroup_resource_limits
     src/tests/util/file_area_freelist
     src/tests/util/generation_hold_list
-    src/tests/util/generation_holder
     src/tests/util/generationhandler
     src/tests/util/generationhandler_stress
     src/tests/util/hamming
diff --git a/vespalib/src/tests/datastore/fixed_size_hash_map/fixed_size_hash_map_test.cpp b/vespalib/src/tests/datastore/fixed_size_hash_map/fixed_size_hash_map_test.cpp
index 599cb209e6c..ad10bc5c7e6 100644
--- a/vespalib/src/tests/datastore/fixed_size_hash_map/fixed_size_hash_map_test.cpp
+++ b/vespalib/src/tests/datastore/fixed_size_hash_map/fixed_size_hash_map_test.cpp
@@ -90,11 +90,11 @@ DataStoreFixedSizeHashTest::commit()
 {
     _store.transferHoldLists(_generation_handler.getCurrentGeneration());
     _hash_map->transfer_hold_lists(_generation_handler.getCurrentGeneration());
-    _generation_holder.transferHoldLists(_generation_handler.getCurrentGeneration());
+    _generation_holder.assign_generation(_generation_handler.getCurrentGeneration());
     _generation_handler.incGeneration();
     _store.trimHoldLists(_generation_handler.getFirstUsedGeneration());
     _hash_map->trim_hold_lists(_generation_handler.getFirstUsedGeneration());
-    _generation_holder.trimHoldLists(_generation_handler.getFirstUsedGeneration());
+    _generation_holder.reclaim(_generation_handler.getFirstUsedGeneration());
 }
 
 size_t
diff --git a/vespalib/src/tests/util/generation_hold_list/generation_hold_list_test.cpp b/vespalib/src/tests/util/generation_hold_list/generation_hold_list_test.cpp
index 0490a99f1e0..8305b711d5f 100644
--- a/vespalib/src/tests/util/generation_hold_list/generation_hold_list_test.cpp
+++ b/vespalib/src/tests/util/generation_hold_list/generation_hold_list_test.cpp
@@ -3,12 +3,13 @@
 #include <vespa/vespalib/gtest/gtest.h>
 #include <vespa/vespalib/util/generation_hold_list.hpp>
 #include <vespa/vespalib/util/generationholder.h>
+#include <iostream>
 
 using vespalib::GenerationHeldBase;
 using vespalib::GenerationHoldList;
 
 using MyElem = GenerationHeldBase;
-using MyHoldList = GenerationHoldList<MyElem::UP, true>;
+using MyHoldList = GenerationHoldList<MyElem::UP, true, false>;
 
 TEST(GenerationHoldListTest, holding_of_unique_ptr_elements_with_tracking_of_held_bytes)
 {
diff --git a/vespalib/src/tests/util/generation_holder/CMakeLists.txt b/vespalib/src/tests/util/generation_holder/CMakeLists.txt
deleted file mode 100644
index 8acf9fadaff..00000000000
--- a/vespalib/src/tests/util/generation_holder/CMakeLists.txt
+++ /dev/null
@@ -1,9 +0,0 @@
-# Copyright Yahoo. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
-vespa_add_executable(vespalib_generation_holder_test_app TEST
-    SOURCES
-    generation_holder_test.cpp
-    DEPENDS
-    vespalib
-    GTest::GTest
-)
-vespa_add_test(NAME vespalib_generation_holder_test_app COMMAND vespalib_generation_holder_test_app)
diff --git a/vespalib/src/tests/util/generation_holder/generation_holder_test.cpp b/vespalib/src/tests/util/generation_holder/generation_holder_test.cpp
deleted file mode 100644
index 97c3330ac9e..00000000000
--- a/vespalib/src/tests/util/generation_holder/generation_holder_test.cpp
+++ /dev/null
@@ -1,38 +0,0 @@
-// Copyright Yahoo. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
-
-#include <vespa/vespalib/gtest/gtest.h>
-#include <vespa/vespalib/util/generationholder.h>
-
-using vespalib::GenerationHolder;
-using MyHeld = vespalib::GenerationHeldBase;
-
-TEST(GenerationHolderTest, basic_tracking)
-{
-    GenerationHolder gh;
-    gh.hold(std::make_unique<MyHeld>(sizeof(int32_t)));
-    gh.transferHoldLists(0);
-    gh.hold(std::make_unique<MyHeld>(sizeof(int32_t)));
-    gh.transferHoldLists(1);
-    gh.hold(std::make_unique<MyHeld>(sizeof(int32_t)));
-    gh.transferHoldLists(2);
-    gh.hold(std::make_unique<MyHeld>(sizeof(int32_t)));
-    gh.transferHoldLists(4);
-    EXPECT_EQ(4u * sizeof(int32_t), gh.getHeldBytes());
-    gh.trimHoldLists(0);
-    EXPECT_EQ(4u * sizeof(int32_t), gh.getHeldBytes());
-    gh.trimHoldLists(1);
-    EXPECT_EQ(3u * sizeof(int32_t), gh.getHeldBytes());
-    gh.trimHoldLists(2);
-    EXPECT_EQ(2u * sizeof(int32_t), gh.getHeldBytes());
-    gh.hold(std::make_unique<MyHeld>(sizeof(int32_t)));
-    gh.transferHoldLists(6);
-    EXPECT_EQ(3u * sizeof(int32_t), gh.getHeldBytes());
-    gh.trimHoldLists(6);
-    EXPECT_EQ(1u * sizeof(int32_t), gh.getHeldBytes());
-    gh.trimHoldLists(7);
-    EXPECT_EQ(0u * sizeof(int32_t), gh.getHeldBytes());
-    gh.trimHoldLists(7);
-    EXPECT_EQ(0u * sizeof(int32_t), gh.getHeldBytes());
-}
-
-GTEST_MAIN_RUN_ALL_TESTS()
diff --git a/vespalib/src/tests/util/rcuvector/rcuvector_test.cpp b/vespalib/src/tests/util/rcuvector/rcuvector_test.cpp
index eb2b00f9e20..c23065b7468 100644
--- a/vespalib/src/tests/util/rcuvector/rcuvector_test.cpp
+++ b/vespalib/src/tests/util/rcuvector/rcuvector_test.cpp
@@ -102,15 +102,15 @@ TEST(RcuVectorTest, resize)
         RcuVectorBase<int8_t> v(growStrategy(16, 1.0, 0), g);
         v.push_back(1);
         v.push_back(2);
-        g.transferHoldLists(0);
-        g.trimHoldLists(1);
+        g.assign_generation(0);
+        g.reclaim(1);
         const int8_t *old = &v[0];
         EXPECT_EQ(16u, v.capacity());
         EXPECT_EQ(2u, v.size());
         v.ensure_size(32, 3);
         v[0] = 3;
         v[1] = 3;
-        g.transferHoldLists(1);
+        g.assign_generation(1);
         EXPECT_EQ(1, old[0]);
         EXPECT_EQ(2, old[1]);
         EXPECT_EQ(3, v[0]);
@@ -119,7 +119,7 @@ TEST(RcuVectorTest, resize)
         EXPECT_EQ(3, v[31]);
         EXPECT_EQ(64u, v.capacity());
         EXPECT_EQ(32u, v.size());
-        g.trimHoldLists(2);
+        g.reclaim(2);
     }
 }
 
@@ -197,11 +197,11 @@ void verify_shrink_with_buffer_copying(size_t initial_size, size_t absolute_mini
     v.push_back(2);
     v.push_back(3);
     v.push_back(4);
-    g.transferHoldLists(0);
-    g.trimHoldLists(1);
+    g.assign_generation(0);
+    g.reclaim(1);
     MemoryUsage mu;
     mu = v.getMemoryUsage();
-    mu.incAllocatedBytesOnHold(g.getHeldBytes());
+    mu.incAllocatedBytesOnHold(g.get_held_bytes());
     EXPECT_TRUE(assertUsage(MemoryUsage(initial_capacity, 4, 0, 0), mu));
     EXPECT_EQ(4u, v.size());
     EXPECT_EQ(initial_capacity, v.capacity());
@@ -211,18 +211,18 @@ void verify_shrink_with_buffer_copying(size_t initial_size, size_t absolute_mini
     EXPECT_EQ(4, v[3]);
     const int8_t *old = &v[0];
     v.shrink(2);
-    g.transferHoldLists(1);
+    g.assign_generation(1);
     EXPECT_EQ(2u, v.size());
     EXPECT_EQ(minimal_capacity, v.capacity());
     EXPECT_EQ(1, v[0]);
     EXPECT_EQ(2, v[1]);
     EXPECT_EQ(1, old[0]);
     EXPECT_EQ(2, old[1]);
-    g.trimHoldLists(2);
+    g.reclaim(2);
     EXPECT_EQ(1, v[0]);
     EXPECT_EQ(2, v[1]);
     mu = v.getMemoryUsage();
-    mu.incAllocatedBytesOnHold(g.getHeldBytes());
+    mu.incAllocatedBytesOnHold(g.get_held_bytes());
     EXPECT_TRUE(assertUsage(MemoryUsage(minimal_capacity, 2, 0, 0), mu));
 }
 
@@ -256,7 +256,7 @@ struct ShrinkFixture {
         EXPECT_EQ(oldPtr, &vec[0]);
     }
     void assertEmptyHoldList() {
-        EXPECT_EQ(0u, g.getHeldBytes());
+        EXPECT_EQ(0u, g.get_held_bytes());
     }
     static size_t page_ints() { return round_up_to_page_size(1) / sizeof(int); }
 };
@@ -294,8 +294,8 @@ TEST(RcuVectorTest, small_expand)
     v.push_back(2);
     EXPECT_EQ(2u, v.capacity());
     EXPECT_EQ(2u, v.size());
-    g.transferHoldLists(1);
-    g.trimHoldLists(2);
+    g.assign_generation(1);
+    g.reclaim(2);
 }
 
 struct FixtureBase {
@@ -325,10 +325,10 @@ struct Fixture : public FixtureBase {
 
     Fixture();
     ~Fixture();
-    void transfer_and_trim(generation_t transfer_gen, generation_t trim_gen)
+    void assign_and_reclaim(generation_t assign_gen, generation_t reclaim_gen)
     {
-        g.transferHoldLists(transfer_gen);
-        g.trimHoldLists(trim_gen);
+        g.assign_generation(assign_gen);
+        g.reclaim(reclaim_gen);
     }
 };
 
@@ -345,7 +345,7 @@ TEST(RcuVectorTest, memory_allocator_can_be_set)
 {
     Fixture f;
     EXPECT_EQ(AllocStats(2, 0), f.stats);
-    f.transfer_and_trim(1, 2);
+    f.assign_and_reclaim(1, 2);
     EXPECT_EQ(AllocStats(2, 1), f.stats);
 }
 
@@ -355,7 +355,7 @@ TEST(RcuVectorTest, memory_allocator_is_preserved_across_reset)
     f.arr.reset();
     f.arr.reserve(100);
     EXPECT_EQ(AllocStats(4, 1), f.stats);
-    f.transfer_and_trim(1, 2);
+    f.assign_and_reclaim(1, 2);
     EXPECT_EQ(AllocStats(4, 3), f.stats);
 }
 
@@ -366,7 +366,7 @@ TEST(RcuVectorTest, created_replacement_vector_uses_same_memory_allocator)
     EXPECT_EQ(AllocStats(2, 0), f.stats);
     arr2.reserve(100);
     EXPECT_EQ(AllocStats(3, 0), f.stats);
-    f.transfer_and_trim(1, 2);
+    f.assign_and_reclaim(1, 2);
     EXPECT_EQ(AllocStats(3, 1), f.stats);
 }
 
@@ -377,7 +377,7 @@ TEST(RcuVectorTest, ensure_size_and_shrink_use_same_memory_allocator)
     EXPECT_EQ(AllocStats(3, 0), f.stats);
     f.arr.shrink(1000);
     EXPECT_EQ(AllocStats(4, 0), f.stats);
-    f.transfer_and_trim(1, 2);
+    f.assign_and_reclaim(1, 2);
     EXPECT_EQ(AllocStats(4, 3), f.stats);
 }
 
@@ -432,10 +432,10 @@ void
 StressFixture::commit()
 {
     auto current_gen = generation_handler.getCurrentGeneration();
-    g.transferHoldLists(current_gen);
+    g.assign_generation(current_gen);
     generation_handler.incGeneration();
     auto first_used_gen = generation_handler.getFirstUsedGeneration();
-    g.trimHoldLists(first_used_gen);
+    g.reclaim(first_used_gen);
 }
 
 void
diff --git a/vespalib/src/vespa/vespalib/datastore/datastorebase.cpp b/vespalib/src/vespa/vespalib/datastore/datastorebase.cpp
index dd6c767e9c6..5962e6cf2f7 100644
--- a/vespalib/src/vespa/vespalib/datastore/datastorebase.cpp
+++ b/vespalib/src/vespa/vespalib/datastore/datastorebase.cpp
@@ -232,7 +232,7 @@ DataStoreBase::transferElemHoldList(generation_t generation)
 void
 DataStoreBase::transferHoldLists(generation_t generation)
 {
-    _genHolder.transferHoldLists(generation);
+    _genHolder.assign_generation(generation);
     if (hasElemHold1()) {
         transferElemHoldList(generation);
     }
@@ -250,7 +250,7 @@ void
 DataStoreBase::trimHoldLists(generation_t usedGen)
 {
     trimElemHoldList(usedGen);  // Trim entries before trimming buffers
-    _genHolder.trimHoldLists(usedGen);
+    _genHolder.reclaim(usedGen);
 }
 
 void
@@ -258,7 +258,7 @@ DataStoreBase::clearHoldLists()
 {
     transferElemHoldList(0);
     clearElemHoldList();
-    _genHolder.clearHoldLists();
+    _genHolder.reclaim_all();
 }
 
 void
@@ -268,7 +268,7 @@ DataStoreBase::dropBuffers()
     for (uint32_t bufferId = 0; bufferId < numBuffers; ++bufferId) {
         _states[bufferId].dropBuffer(bufferId, _buffers[bufferId].get_atomic_buffer());
     }
-    _genHolder.clearHoldLists();
+    _genHolder.reclaim_all();
 }
 
 vespalib::MemoryUsage
@@ -289,7 +289,7 @@ DataStoreBase::holdBuffer(uint32_t bufferId)
     _states[bufferId].onHold(bufferId);
     size_t holdBytes = 0u;  // getMemStats() still accounts held buffers
     auto hold = std::make_unique<BufferHold>(holdBytes, *this, bufferId);
-    _genHolder.hold(std::move(hold));
+    _genHolder.insert(std::move(hold));
 }
 
 void
@@ -356,7 +356,7 @@ DataStoreBase::getMemStats() const
             LOG_ABORT("should not be reached");
         }
     }
-    size_t genHolderHeldBytes = _genHolder.getHeldBytes();
+    size_t genHolderHeldBytes = _genHolder.get_held_bytes();
     stats._holdBytes += genHolderHeldBytes;
     stats._allocBytes += genHolderHeldBytes;
     stats._usedBytes += genHolderHeldBytes;
@@ -428,7 +428,7 @@ DataStoreBase::fallbackResize(uint32_t bufferId, size_t elemsNeeded)
                                                state.getTypeHandler(),
                                                state.getTypeId());
     if (!_initializing) {
-        _genHolder.hold(std::move(hold));
+        _genHolder.insert(std::move(hold));
     }
 }
 
diff --git a/vespalib/src/vespa/vespalib/datastore/sharded_hash_map.cpp b/vespalib/src/vespa/vespalib/datastore/sharded_hash_map.cpp
index 2ae22084472..102aa1cefb3 100644
--- a/vespalib/src/vespa/vespalib/datastore/sharded_hash_map.cpp
+++ b/vespalib/src/vespa/vespalib/datastore/sharded_hash_map.cpp
@@ -32,7 +32,7 @@ ShardedHashMap::ShardedHashMap(std::unique_ptr<const EntryComparator> comp)
 
 ShardedHashMap::~ShardedHashMap()
 {
-    _gen_holder.clearHoldLists();
+    _gen_holder.reclaim_all();
     for (size_t i = 0; i < num_shards; ++i) {
         auto map = _maps[i].load(std::memory_order_relaxed);
         delete map;
@@ -58,7 +58,7 @@ ShardedHashMap::hold_shard(std::unique_ptr<const FixedSizeHashMap> map)
 {
     auto usage = map->get_memory_usage();
     auto hold = std::make_unique<ShardedHashMapShardHeld>(usage.allocatedBytes(), std::move(map));
-    _gen_holder.hold(std::move(hold));
+    _gen_holder.insert(std::move(hold));
 }
 
 ShardedHashMap::KvType&
@@ -115,7 +115,7 @@ ShardedHashMap::transfer_hold_lists(generation_t generation)
             map->transfer_hold_lists(generation);
         }
     }
-    _gen_holder.transferHoldLists(generation);
+    _gen_holder.assign_generation(generation);
 }
 
 void
@@ -127,7 +127,7 @@ ShardedHashMap::trim_hold_lists(generation_t first_used)
             map->trim_hold_lists(first_used);
         }
     }
-    _gen_holder.trimHoldLists(first_used);
+    _gen_holder.reclaim(first_used);
 }
 
 size_t
@@ -153,7 +153,7 @@ ShardedHashMap::get_memory_usage() const
             memory_usage.merge(map->get_memory_usage());
         }
     }
-    size_t gen_holder_held_bytes = _gen_holder.getHeldBytes();
+    size_t gen_holder_held_bytes = _gen_holder.get_held_bytes();
     memory_usage.incAllocatedBytes(gen_holder_held_bytes);
     memory_usage.incAllocatedBytesOnHold(gen_holder_held_bytes);
     return memory_usage;
@@ -222,7 +222,7 @@ ShardedHashMap::foreach_value(std::function<void(const std::vector<EntryRef>&)>
 bool
 ShardedHashMap::has_held_buffers() const
 {
-    return _gen_holder.getHeldBytes() != 0;
+    return _gen_holder.get_held_bytes() != 0;
 }
 
 void
diff --git a/vespalib/src/vespa/vespalib/util/generation_hold_list.h b/vespalib/src/vespa/vespalib/util/generation_hold_list.h
index 5e12cb72bbd..b2f90934e84 100644
--- a/vespalib/src/vespa/vespalib/util/generation_hold_list.h
+++ b/vespalib/src/vespa/vespalib/util/generation_hold_list.h
@@ -14,7 +14,7 @@ namespace vespalib {
  *
  * This class must be used in accordance with a GenerationHandler.
  */
-template <typename T, bool track_bytes_held>
+template <typename T, bool track_bytes_held, bool use_deque>
 class GenerationHoldList {
 private:
     using generation_t = vespalib::GenerationHandler::generation_t;
@@ -30,7 +30,9 @@ private:
     };
 
     using ElemList = std::vector<T>;
-    using ElemWithGenList = std::deque<ElemWithGen>;
+    using ElemWithGenList = std::conditional_t<use_deque,
+            std::deque<ElemWithGen>,
+            std::vector<ElemWithGen>>;
 
     ElemList _phase_1_list;
     ElemWithGenList _phase_2_list;
@@ -46,6 +48,7 @@ private:
 
 public:
     GenerationHoldList();
+    ~GenerationHoldList();
 
     /**
      * Insert the given data element on this hold list.
diff --git a/vespalib/src/vespa/vespalib/util/generation_hold_list.hpp b/vespalib/src/vespa/vespalib/util/generation_hold_list.hpp
index e7eee2b0aef..ed4a99c4753 100644
--- a/vespalib/src/vespa/vespalib/util/generation_hold_list.hpp
+++ b/vespalib/src/vespa/vespalib/util/generation_hold_list.hpp
@@ -1,12 +1,15 @@
 // Copyright Yahoo. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
 
+#pragma once
+
 #include "generation_hold_list.h"
+#include <cassert>
 
 namespace vespalib {
 
-template <typename T, bool track_bytes_held>
+template <typename T, bool track_bytes_held, bool use_deque>
 void
-GenerationHoldList<T, track_bytes_held>::assign_generation_internal(generation_t current_gen)
+GenerationHoldList<T, track_bytes_held, use_deque>::assign_generation_internal(generation_t current_gen)
 {
     for (auto& elem : _phase_1_list) {
         _phase_2_list.push_back(ElemWithGen(std::move(elem), current_gen));
@@ -14,9 +17,9 @@ GenerationHoldList<T, track_bytes_held>::assign_generation_internal(generation_t
     _phase_1_list.clear();
 }
 
-template <typename T, bool track_bytes_held>
+template <typename T, bool track_bytes_held, bool use_deque>
 void
-GenerationHoldList<T, track_bytes_held>::reclaim_internal(generation_t oldest_used_gen)
+GenerationHoldList<T, track_bytes_held, use_deque>::reclaim_internal(generation_t oldest_used_gen)
 {
     auto itr = _phase_2_list.begin();
     auto ite = _phase_2_list.end();
@@ -33,17 +36,25 @@ GenerationHoldList<T, track_bytes_held>::reclaim_internal(generation_t oldest_us
     }
 }
 
-template <typename T, bool track_bytes_held>
-GenerationHoldList<T, track_bytes_held>::GenerationHoldList()
+template <typename T, bool track_bytes_held, bool use_deque>
+GenerationHoldList<T, track_bytes_held, use_deque>::GenerationHoldList()
     : _phase_1_list(),
       _phase_2_list(),
       _held_bytes()
 {
 }
 
-template <typename T, bool track_bytes_held>
+template <typename T, bool track_bytes_held, bool use_deque>
+GenerationHoldList<T, track_bytes_held, use_deque>::~GenerationHoldList()
+{
+    assert(_phase_1_list.empty());
+    assert(_phase_2_list.empty());
+    assert(get_held_bytes() == 0);
+}
+
+template <typename T, bool track_bytes_held, bool use_deque>
 void
-GenerationHoldList<T, track_bytes_held>::insert(T data)
+GenerationHoldList<T, track_bytes_held, use_deque>::insert(T data)
 {
     _phase_1_list.push_back(std::move(data));
     if (track_bytes_held) {
@@ -51,9 +62,9 @@ GenerationHoldList<T, track_bytes_held>::insert(T data)
     }
 }
 
-template <typename T, bool track_bytes_held>
+template <typename T, bool track_bytes_held, bool use_deque>
 void
-GenerationHoldList<T, track_bytes_held>::reclaim_all()
+GenerationHoldList<T, track_bytes_held, use_deque>::reclaim_all()
 {
     _phase_1_list.clear();
     _phase_2_list.clear();
diff --git a/vespalib/src/vespa/vespalib/util/generationholder.cpp b/vespalib/src/vespa/vespalib/util/generationholder.cpp
index f2b10ff3af1..5f31f610c68 100644
--- a/vespalib/src/vespa/vespalib/util/generationholder.cpp
+++ b/vespalib/src/vespa/vespalib/util/generationholder.cpp
@@ -1,66 +1,15 @@
 // Copyright Yahoo. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
 
 #include "generationholder.h"
-#include <cassert>
+#include "generation_hold_list.hpp"
 
 namespace vespalib {
 
 GenerationHeldBase::~GenerationHeldBase() = default;
 
 GenerationHolder::GenerationHolder()
-    : _hold1List(),
-      _hold2List(),
-      _heldBytes(0)
-{ }
-
-GenerationHolder::~GenerationHolder()
-{
-    assert(_hold1List.empty());
-    assert(_hold2List.empty());
-    assert(getHeldBytes() == 0);
-}
-
-void
-GenerationHolder::hold(GenerationHeldBase::UP data)
-{
-    _hold1List.push_back(std::move(data));
-    _heldBytes.store(getHeldBytes() + _hold1List.back()->byte_size(), std::memory_order_relaxed);
-}
-
-void
-GenerationHolder::transferHoldListsSlow(generation_t generation)
-{
-    HoldList::iterator it(_hold1List.begin());
-    HoldList::iterator ite(_hold1List.end());
-    HoldList &hold2List = _hold2List;
-    for (; it != ite; ++it) {
-        assert((*it)->_generation == 0u);
-        (*it)->_generation = generation;
-        hold2List.push_back(std::move(*it));
-    }
-    _hold1List.clear();
-}
-
-void
-GenerationHolder::trimHoldListsSlow(generation_t usedGen)
-{
-    for (;;) {
-        if (_hold2List.empty())
-            break;
-        GenerationHeldBase &first = *_hold2List.front();
-        if (static_cast<sgeneration_t>(first._generation - usedGen) >= 0)
-            break;
-        _heldBytes.store(getHeldBytes() - first.byte_size(), std::memory_order_relaxed);
-        _hold2List.erase(_hold2List.begin());
-    }
-}
-
-void
-GenerationHolder::clearHoldLists()
+    : GenerationHoldList<GenerationHeldBase::UP, true, false>()
 {
-    _hold1List.clear();
-    _hold2List.clear();
-    _heldBytes = 0;
 }
 
 }
diff --git a/vespalib/src/vespa/vespalib/util/generationholder.h b/vespalib/src/vespa/vespalib/util/generationholder.h
index df44f39ebff..ec2cded2e84 100644
--- a/vespalib/src/vespa/vespalib/util/generationholder.h
+++ b/vespalib/src/vespa/vespalib/util/generationholder.h
@@ -2,8 +2,8 @@
 
 #pragma once
 
+#include "generation_hold_list.h"
 #include "generationhandler.h"
-#include <vector>
 #include <memory>
 
 namespace vespalib {
@@ -11,79 +11,31 @@ namespace vespalib {
 class GenerationHeldBase
 {
 public:
-    typedef GenerationHandler::generation_t generation_t;
-    typedef std::unique_ptr<GenerationHeldBase> UP;
-    typedef std::shared_ptr<GenerationHeldBase> SP;
+    using generation_t = GenerationHandler::generation_t;
+    using UP = std::unique_ptr<GenerationHeldBase>;
+    using SP = std::shared_ptr<GenerationHeldBase>;
 
-    generation_t _generation;
 private:
     size_t	 _byte_size;
 
 public:
     GenerationHeldBase(size_t byte_size_in)
-        : _generation(0u),
-          _byte_size(byte_size_in)
+        : _byte_size(byte_size_in)
     { }
 
     virtual ~GenerationHeldBase();
     size_t byte_size() const { return _byte_size; }
 };
 
+template class GenerationHoldList<GenerationHeldBase::UP, true, false>;
+
 /*
  * GenerationHolder is meant to hold large elements until readers can
  * no longer access them.
  */
-class GenerationHolder
-{
-private:
-    typedef GenerationHandler::generation_t generation_t;
-    typedef GenerationHandler::sgeneration_t sgeneration_t;
-
-    typedef std::vector<GenerationHeldBase::UP> HoldList;
-
-    HoldList _hold1List;
-    HoldList _hold2List;
-    std::atomic<size_t>   _heldBytes;
-
-    /**
-     * Transfer holds from hold1 to hold2 lists, assigning generation.
-     */
-    void transferHoldListsSlow(generation_t generation);
-
-    /**
-     * Remove all data elements from this holder where generation < usedGen.
-     **/
-    void trimHoldListsSlow(generation_t usedGen);
-
+class GenerationHolder : public GenerationHoldList<GenerationHeldBase::UP, true, false> {
 public:
     GenerationHolder();
-    ~GenerationHolder();
-
-    /**
-     * Add the given data pointer to this holder.
-     **/
-    void hold(GenerationHeldBase::UP data);
-
-    /**
-     * Transfer holds from hold1 to hold2 lists, assigning generation.
-     */
-    void transferHoldLists(generation_t generation) {
-        if (!_hold1List.empty()) {
-            transferHoldListsSlow(generation);
-        }
-    }
-
-    /**
-     * Remove all data elements from this holder where generation < usedGen.
-     **/
-    void trimHoldLists(generation_t usedGen) {
-        if (!_hold2List.empty() && static_cast<sgeneration_t>(_hold2List.front()->_generation - usedGen) < 0) {
-            trimHoldListsSlow(usedGen);
-        }
-    }
-
-    void clearHoldLists();
-    size_t getHeldBytes() const { return _heldBytes.load(std::memory_order_relaxed); }
 };
 
 }
diff --git a/vespalib/src/vespa/vespalib/util/rcuvector.hpp b/vespalib/src/vespa/vespalib/util/rcuvector.hpp
index 97a73a73cc9..e551bb17db0 100644
--- a/vespalib/src/vespa/vespalib/util/rcuvector.hpp
+++ b/vespalib/src/vespa/vespalib/util/rcuvector.hpp
@@ -80,7 +80,7 @@ RcuVectorBase<T>::replaceVector(ArrayType replacement) {
     replacement.swap(_data); // atomic switch of underlying data
     size_t holdSize = replacement.capacity() * sizeof(T);
     auto hold = std::make_unique<RcuVectorHeld<ArrayType>>(holdSize, std::move(replacement));
-    _genHolder.hold(std::move(hold));
+    _genHolder.insert(std::move(hold));
     onReallocation();
 }
 
@@ -116,7 +116,7 @@ RcuVectorBase<T>::shrink(size_t newSize)
         tmpData.swap(_data); // atomic switch of underlying data
         size_t holdSize = tmpData.capacity() * sizeof(T);
         auto hold = std::make_unique<RcuVectorHeld<ArrayType>>(holdSize, std::move(tmpData));
-        _genHolder.hold(std::move(hold));
+        _genHolder.insert(std::move(hold));
         onReallocation();
     }
 }
@@ -162,7 +162,7 @@ template <typename T>
 void
 RcuVector<T>::onReallocation() {
     RcuVectorBase<T>::onReallocation();
-    _genHolderStore.transferHoldLists(_generation);
+    _genHolderStore.assign_generation(_generation);
 }
 
 template <typename T>
@@ -182,14 +182,14 @@ RcuVector<T>::RcuVector(GrowStrategy growStrategy)
 template <typename T>
 RcuVector<T>::~RcuVector()
 {
-    _genHolderStore.clearHoldLists();
+    _genHolderStore.reclaim_all();
 }
 
 template <typename T>
 void
 RcuVector<T>::removeOldGenerations(generation_t firstUsed)
 {
-    _genHolderStore.trimHoldLists(firstUsed);
+    _genHolderStore.reclaim(firstUsed);
 }
 
 template <typename T>
@@ -197,7 +197,7 @@ MemoryUsage
 RcuVector<T>::getMemoryUsage() const
 {
     MemoryUsage retval(RcuVectorBase<T>::getMemoryUsage());
-    retval.mergeGenerationHeldBytes(_genHolderStore.getHeldBytes());
+    retval.mergeGenerationHeldBytes(_genHolderStore.get_held_bytes());
     return retval;
 }