depgraph: add memory usage control (feature)

Co-Authored-By: Lőrinc <pap.lorinc@gmail.com>

src/cluster_linearize.h

@@ -12,6 +12,7 @@
 #include <utility>
 #include <vector>
 
+#include <memusage.h>
 #include <random.h>
 #include <span.h>
 #include <util/feefrac.h>
@@ -332,6 +333,17 @@ public:
         }
         return true;
     }
+
+    /** Reduce memory usage if possible. No observable effect. */
+    void Compact() noexcept
+    {
+        entries.shrink_to_fit();
+    }
+
+    size_t DynamicMemoryUsage() const noexcept
+    {
+        return memusage::DynamicUsage(entries);
+    }
 };
 
 /** A set of transactions together with their aggregate feerate. */

src/test/fuzz/cluster_linearize.cpp

@@ -452,9 +452,13 @@ FUZZ_TARGET(clusterlin_depgraph_sim)
         }
     };
 
+    auto last_compaction_pos{real.PositionRange()};
+
     LIMITED_WHILE(provider.remaining_bytes() > 0, 1000) {
-        uint8_t command = provider.ConsumeIntegral<uint8_t>();
+        int command = provider.ConsumeIntegral<uint8_t>() % 4;
-        if (num_tx_sim == 0 || ((command % 3) <= 0 && num_tx_sim < TestBitSet::Size())) {
+        while (true) {
+            // Iterate decreasing command until an applicable branch is found.
+            if (num_tx_sim < TestBitSet::Size() && command-- == 0) {
                 // AddTransaction.
                 auto fee = provider.ConsumeIntegralInRange<int64_t>(-0x8000000000000, 0x7ffffffffffff);
                 auto size = provider.ConsumeIntegralInRange<int32_t>(1, 0x3fffff);
@@ -472,9 +476,8 @@ FUZZ_TARGET(clusterlin_depgraph_sim)
                 // Update sim.
                 sim[idx] = {feerate, TestBitSet::Singleton(idx)};
                 ++num_tx_sim;
-            continue;
+                break;
-        }
+            } else if (num_tx_sim > 0 && command-- == 0) {
-        if ((command % 3) <= 1 && num_tx_sim > 0) {
                 // AddDependencies.
                 DepGraphIndex child = idx_fn();
                 auto parents = subset_fn();
@@ -482,9 +485,8 @@ FUZZ_TARGET(clusterlin_depgraph_sim)
                 real.AddDependencies(parents, child);
                 // Apply to sim.
                 sim[child]->second |= parents;
-            continue;
+                break;
-        }
+            } else if (num_tx_sim > 0 && command-- == 0) {
-        if (num_tx_sim > 0) {
                 // Remove transactions.
                 auto del = set_fn();
                 // Propagate all ancestry information before deleting anything in the simulation (as
@@ -505,10 +507,17 @@ FUZZ_TARGET(clusterlin_depgraph_sim)
                         }
                     }
                 }
-            continue;
+                break;
+            } else if (command-- == 0) {
+                // Compact.
+                const size_t mem_before{real.DynamicMemoryUsage()};
+                real.Compact();
+                const size_t mem_after{real.DynamicMemoryUsage()};
+                assert(real.PositionRange() < last_compaction_pos ? mem_after < mem_before : mem_after <= mem_before);
+                last_compaction_pos = real.PositionRange();
+                break;
+            }
         }
-        // This should be unreachable (one of the 3 above actions should always be possible).
-        assert(false);
     }
 
     // Compare the real obtained depgraph against the simulation.