Estimate datastore stash memory usage instead of sampling it.

2 files changed, 19 insertions, 1 deletions

diff --git a/vespalib/src/vespa/vespalib/datastore/datastorebase.cpp b/vespalib/src/vespa/vespalib/datastore/datastorebase.cpp
index 5c88900ae92..b5328134e4f 100644
--- a/vespalib/src/vespa/vespalib/datastore/datastorebase.cpp
+++ b/vespalib/src/vespa/vespalib/datastore/datastorebase.cpp
@@ -295,7 +295,7 @@ DataStoreBase::getMemoryUsage() const {
     extra_used += _free_lists.size() * sizeof(FreeList);
     usage.incAllocatedBytes(extra_allocated);
     usage.incUsedBytes(extra_used);
-    usage.merge(_stash.get_memory_usage());
+    merge_stash_memory_usage(usage);
     return usage;
 }
 
@@ -526,4 +526,20 @@ DataStoreBase::inc_hold_buffer_count()
     ++_hold_buffer_count;
 }
 
+void
+DataStoreBase::merge_stash_memory_usage(vespalib::MemoryUsage& usage) const
+{
+    /*
+     * Estimate stash memory usage instead of sampling it to avoid race
+     * with writer thread.
+     */
+    uint32_t buffer_states = get_bufferid_limit_acquire();
+    size_t stashed_buffer_state_size = sizeof(BufferState) + sizeof(stash::DestructObject<BufferState>);
+    size_t chunk_size = _stash.get_chunk_size();
+    uint32_t buffer_states_per_chunk = (chunk_size - sizeof(stash::Chunk)) / stashed_buffer_state_size;
+    uint32_t chunks = (buffer_states + buffer_states_per_chunk - 1) / buffer_states_per_chunk;
+    usage.incAllocatedBytes(chunks * chunk_size);
+    usage.incUsedBytes(buffer_states * stashed_buffer_state_size + chunks * sizeof(stash::Chunk));
+}
+
 }
diff --git a/vespalib/src/vespa/vespalib/datastore/datastorebase.h b/vespalib/src/vespa/vespalib/datastore/datastorebase.h
index b91d6c7cfa6..d7ae20a7028 100644
--- a/vespalib/src/vespa/vespalib/datastore/datastorebase.h
+++ b/vespalib/src/vespa/vespalib/datastore/datastorebase.h
@@ -261,6 +261,8 @@ private:
 
     virtual void reclaim_all_entry_refs() = 0;
 
+    void merge_stash_memory_usage(vespalib::MemoryUsage& usage) const;
+
     std::vector<BufferAndMeta>    _buffers; // For fast mapping with known types
 
     // Provides a mapping from typeId -> primary buffer for that type.