diff --git a/java/src/main/java/org/softwareheritage/graph/utils/TopoSort.java b/java/src/main/java/org/softwareheritage/graph/utils/TopoSort.java
index 9866f6b..259dcce 100644
--- a/java/src/main/java/org/softwareheritage/graph/utils/TopoSort.java
+++ b/java/src/main/java/org/softwareheritage/graph/utils/TopoSort.java
@@ -1,125 +1,134 @@
 /*
  * Copyright (c) 2022 The Software Heritage developers
  * See the AUTHORS file at the top-level directory of this distribution
  * License: GNU General Public License version 3, or any later version
  * See top-level LICENSE file for more information
  */
 
 package org.softwareheritage.graph.utils;
 
 import com.martiansoftware.jsap.*;
 import it.unimi.dsi.big.webgraph.LazyLongIterator;
 import it.unimi.dsi.big.webgraph.NodeIterator;
 import org.softwareheritage.graph.*;
 
 import java.io.IOException;
 import java.util.*;
 
+/* Lists all nodes nodes of the types given as argument, in topological order,
+ * from leaves (contents, if selected) to the top (origins, if selected).
+ *
+ * This uses a DFS, so nodes are likely to be close to their neighbors.
+ *
+ * Some extra information is provided to allow more efficient consumption
+ * of the output: number of ancestors, successors, and a sample of two ancestors.
+ *
+ * Sample invocation:
+ *
+ *   $ java -cp ~/swh-environment/swh-graph/java/target/swh-graph-*.jar -Xmx1000G -XX:PretenureSizeThreshold=512M -XX:MaxNewSize=4G -XX:+UseLargePages -XX:+UseTransparentHugePages -XX:+UseNUMA -XX:+UseTLAB -XX:+ResizeTLAB org.softwareheritage.graph.utils.TopoSort /dev/shm/swh-graph/default/graph 'rev,rel,snp,ori' \
+ *      | pv --line-mode --wait \
+ *      | zstdmt \
+ *      > /poolswh/softwareheritage/vlorentz/2022-04-25_toposort_rev,rel,snp,ori.txt.zst
+ */
+
 public class TopoSort {
     private Subgraph graph;
     private Subgraph transposedGraph;
 
     public static void main(String[] args) throws IOException, ClassNotFoundException {
         if (args.length != 2) {
             System.err.println("Syntax: java org.softwareheritage.graph.utils.TopoSort <path/to/graph> <nodeTypes>");
             System.exit(1);
         }
         String graphPath = args[0];
         String nodeTypes = args[1];
 
         TopoSort toposort = new TopoSort();
 
         toposort.load_graph(graphPath, nodeTypes);
         toposort.toposortDFS();
     }
 
     public void load_graph(String graphBasename, String nodeTypes) throws IOException {
         System.err.println("Loading graph " + graphBasename + " ...");
         var underlyingGraph = SwhBidirectionalGraph.loadMapped(graphBasename);
         System.err.println("Selecting subgraphs.");
         graph = new Subgraph(underlyingGraph, new AllowedNodes(nodeTypes));
         transposedGraph = graph.transpose();
         System.err.println("Graph loaded.");
     }
 
     /* Prints nodes in topological order, based on a DFS. */
     public void toposortDFS() {
         HashSet<Long> visited = new HashSet<Long>();
         Stack<Long> ready = new Stack<>();
 
         /* First, push all leaves to the stack */
         System.err.println("Listing leaves.");
         long total_nodes = 0;
         NodeIterator nodeIterator = graph.nodeIterator();
         for (long currentNodeId = nodeIterator.nextLong(); nodeIterator
                 .hasNext(); currentNodeId = nodeIterator.nextLong()) {
             total_nodes++;
-            // SWHID currentNodeSWHID = graph.getSWHID(currentNodeId);
-            // if (graph.outdegree(currentNodeId) > 0) {
             long firstSuccessor = graph.successors(currentNodeId).nextLong();
             if (firstSuccessor != -1) {
                 /* The node has ancestor, so it is not a leaf. */
-                // SWHID firstSuccessorNodeSWHID = graph.getSWHID(firstSuccessor);
-                // System.err.format("not leaf: %s, has succ: %s\n", currentNodeSWHID, firstSuccessorNodeSWHID);
                 continue;
             }
-            // System.err.format("is leaf: %s\n", currentNodeSWHID);
             ready.push(currentNodeId);
             if (ready.size() % 10000000 == 0) {
                 float ready_size_f = ready.size();
                 float total_nodes_f = total_nodes;
                 System.err.printf("Listed %.02f B leaves (out of %.02f B nodes)\n", ready_size_f / 1000000000.,
                         total_nodes_f / 1000000000.);
             }
         }
         System.err.println("Leaves loaded, starting DFS.");
 
         System.out.format("SWHID,ancestors,successors,sample_ancestor1,sample_ancestor2\n");
         while (!ready.isEmpty()) {
             long currentNodeId = ready.pop();
             visited.add(currentNodeId);
 
             /* Find its successors which are ready */
             LazyLongIterator successors = transposedGraph.successors(currentNodeId);
             long successorCount = 0;
             for (long successorNodeId; (successorNodeId = successors.nextLong()) != -1;) {
                 successorCount++;
                 LazyLongIterator successorAncestors = graph.successors(successorNodeId);
                 boolean isReady = true;
                 for (long successorAncestorNodeId; (successorAncestorNodeId = successorAncestors.nextLong()) != -1;) {
                     if (!visited.contains(successorAncestorNodeId)) {
                         /*
-                         * This ancestor of the success is not yet visited, so the ancestor is not ready.
+                         * This ancestor of the successor is not yet visited, so the ancestor is not ready.
                          */
-                        // SWHID successorNodeSWHID = graph.getSWHID(successorNodeId);
-                        // SWHID successorAncestorNodeSWHID = graph.getSWHID(successorAncestorNodeId);
-                        // System.err.format("successor %s of %s is not ready, has unvisited ancestor: %s\n",
-                        // successorNodeSWHID, currentNodeSWHID, successorAncestorNodeSWHID);
                         isReady = false;
                         break;
                     }
                 }
                 if (isReady) {
                     ready.push(successorNodeId);
                 }
             }
 
             String[] sampleAncestors = {"", ""};
             long ancestorCount = 0;
             LazyLongIterator ancestors = graph.successors(currentNodeId);
             for (long ancestorNodeId; (ancestorNodeId = ancestors.nextLong()) != -1;) {
                 if (ancestorCount < sampleAncestors.length) {
                     sampleAncestors[(int) ancestorCount] = graph.getSWHID(ancestorNodeId).toString();
                 }
                 ancestorCount++;
             }
 
             /*
-             * Print the node TODO: print its depth too?
+             * Print the node
+             *
+             * TODO: print its depth too?
              */
             SWHID currentNodeSWHID = graph.getSWHID(currentNodeId);
             System.out.format("%s,%d,%d,%s,%s\n", currentNodeSWHID, ancestorCount, successorCount, sampleAncestors[0],
                     sampleAncestors[1]);
         }
     }
 }