Find Memory Leaks Not Reported

By default, memlab reports high-confidence memory leaks (filtered out by its built-in leak detector). In case some memory leaks exist but memlab does not report the leaks, this tutorial shows other options to surface suspicious heap objects.

Let's start by running the following command. Make sure to not specify any leak filter in the scenario file. MemLab will apply its built-in leak detectors which find detached DOM elements and unmounted React Fiber nodes. Sometimes this may not detect all (or any) memory leaks.

memlab run --scenario ~/memlab/scenarios/unbound-object.js

Now let's run:

memlab find-leaks --trace-all-objects

This will ask memlab to treat every object allocated by the target interaction as a memory leak. In this case, there are a bunch of objects not released from the target interaction.

memlab clusters the retainer traces of the leaked objects and print them in decreasing order based on the aggregated retained sizes of leak clusters.

MemLab found 46 leak(s)
--Similar leaks in this run: 4--
--Retained size of leaked objects: 8.3MB--
[Window] (native) @35847 [8.3MB]
  --20 (element)--->  [InternalNode] (native) @130981728 [8.3MB]
  --8 (element)--->  [InternalNode] (native) @130980288 [8.3MB]
  --1 (element)--->  [EventListener] (native) @131009888 [8.3MB]
  --1 (element)--->  [V8EventListener] (native) @224808192 [8.3MB]
  --1 (element)--->  [eventHandler] (closure) @168079 [8.3MB]
  --context (internal)--->  [<function scope>] (object) @181905 [8.3MB]
  --bigArray (variable)--->  [Array] (object) @182925 [8.3MB]
  --elements (internal)--->  [(object elements)] (array) @182929 [8.3MB]


--Similar leaks in this run: 79--
--Retained size of leaked objects: 16.9KB--
[Window] (native) @35847 [8.3MB]
  --17 (element)--->  [InternalNode] (native) @224820352 [0 byte]
  --3 (element)--->  [InternalNode] (native) @224766112 [0 byte]
  --1 (element)--->  [InternalNode] (native) @224771072 [0 byte]
  --1 (element)--->  [InternalNode] (native) @224723840 [540 bytes]
  --1 (element)--->  [InternalNode] (native) @224723680 [540 bytes]
  --1 (element)--->  [InternalNode] (native) @224818752 [84 bytes]


--Similar leaks in this run: 62--
--Retained size of leaked objects: 12.8KB--
[Window] (native) @35847 [8.3MB]
  --4 (element)--->  [HTMLDocument] (native) @35845 [6KB]
  --part of key -> value pair in ephemeron table (internal)--->  [HTMLDocument] (object) @167199 [28 bytes]
  --__proto__ (property)--->  [HTMLDocument] (object) @173029 [144 bytes]
  --properties (internal)--->  [(object properties)] (array) @182697 [76 bytes]

...

One way to view the retainer traces in a slightly less verbose would be to apply leak-filter or to use --trace-object-size-above. The below will only show the traces whose retainedSize is greater than 1MB

memlab find-leaks --trace-object-size-above 1000000

The result will look like:

MemLab found 1 leak(s)
--Similar leaks in this run: 4--
--Retained size of leaked objects: 8.3MB--
[Window] (native) @33651 [8.3MB]
  --20 (element)--->  [InternalNode] (native) @216691968 [8.3MB]
  --8 (element)--->  [InternalNode] (native) @216691168 [8.3MB]
  --1 (element)--->  [EventListener] (native) @216563936 [8.3MB]
  --1 (element)--->  [V8EventListener] (native) @216563776 [8.3MB]
  --1 (element)--->  [eventHandler] (closure) @160711 [8.3MB]
  --context (internal)--->  [<function scope>] (object) @176463 [8.3MB]
  --bigArray (variable)--->  [Array] (object) @176465 [8.3MB]
  --elements (internal)--->  [(object elements)] (array) @176489 [8.3MB]

Another options is using --ignore-leak-cluster-size-below which ignore memory leak clusters with aggregated retained size smaller than a specified threshold. To learn more about the find-leaks command, please run memlab find-leaks -h.