diff --git a/.github/workflows/unit-tests.yml b/.github/workflows/unit-tests.yml
index 86748b46de..1f15504724 100644
--- a/.github/workflows/unit-tests.yml
+++ b/.github/workflows/unit-tests.yml
@@ -205,10 +205,15 @@ jobs:
         # pytest once per directory `SHARDS` names, then once over the rest,
         # and every run starts its workers afresh. Each run but the last writes
         # a JUnit file of its own, beside junit.xml; the step fails if any did.
+        #
+        # #2600: run whole, tests/protocols took the workers past the runner's
+        # 16 GB, and its tail stalled past tests._support.time_limit's 30 s. So
+        # its internet, application and misc subpackages run first, each a shard
+        # of its own, and `tests/protocols` then takes the remainder.
         env:
           COVERAGE: ${{ matrix.coverage }}
           LATEST: ${{ matrix.python-version == needs.python-versions.outputs.latest }}
-          SHARDS: ${{ startsWith(matrix.python-version, 'pypy') && 'tests/protocols tests/corekit' || '' }}
+          SHARDS: ${{ startsWith(matrix.python-version, 'pypy') && 'tests/protocols/internet tests/protocols/application tests/protocols/misc tests/protocols tests/corekit' || '' }}
         run: |
           if [ "$LATEST" = "true" ]; then
             if ! skipped=$(python -c "from tests._tiers import project_pin_paths; print(' '.join(project_pin_paths()))"); then
diff --git a/docs/source/contributing/workflows.rst b/docs/source/contributing/workflows.rst
index 520654e75b..4cf70efc97 100644
--- a/docs/source/contributing/workflows.rst
+++ b/docs/source/contributing/workflows.rst
@@ -1046,12 +1046,21 @@ extras cap |cryptography|_ below 46, as 45.0.7 is the newest release with a Linu
 On PyPy an xdist worker's RSS grows with every test it runs, rather than in a few
 heavy modules, so a PyPy leg's ``Run unit tests`` hands its pytest command to
 :file:`util/pytest_shards.py`, as GraalPy's leg does (see below), which runs it once per
-directory its ``SHARDS`` names, ``tests/protocols`` and then ``tests/corekit``, and once
-more over the rest, ignoring each (:issue:`2005`).
+directory its ``SHARDS`` names and once more over the rest, ignoring each
+(:issue:`2005`). The directories are ``tests/protocols/internet``,
+``tests/protocols/application``, ``tests/protocols/misc``, ``tests/protocols`` and
+``tests/corekit``, in that order, so ``tests/protocols`` runs after its own
+subpackages and takes only what they left.
 Each run starts its workers afresh. Measured on PyPy 8.0.1 at ``-n 4``, one run
 over the whole ``ALL`` tier took each worker to 5.4-5.9 GB and the workers together
 past 20 GB, beyond the runner's 16 GB; split, the largest run peaked at 2.6 GB a
-worker and 8.5 GB in all, and the tier took 383 s rather than 493 s. A smaller
+worker and 8.5 GB in all, and the tier took 383 s rather than 493 s. With
+:issue:`2543`'s checksum tests, ``tests/protocols`` run whole outgrew the runner as
+well, and on CI the tests at its tail stalled past ``tests._support.time_limit``'s
+30-second deadline, which counts wall-clock time, so it is split (:issue:`2600`).
+Measured on PyPy 7.3.19 at ``-n 4``, its one run peaked at 17.7 GiB and took 267 s,
+its slowest test 16.4 s; split, the largest of its runs peaked at 5.7 GiB, they took
+224 s together, and the slowest test 11.9 s. A smaller
 ``-n`` would only hand each worker more tests, and a ``PYPY_GC_MAX`` heap cap turns
 the kills into ``MemoryError``\ s. Each run but the last writes a JUnit file of its
 own beside ``junit.xml``, which ``Upload test timings`` takes too, and the step
diff --git a/tests/project/test_pypy_worker_memory_2005.py b/tests/project/test_pypy_worker_memory_2005.py
index 32614a7f73..cb76f87682 100644
--- a/tests/project/test_pypy_worker_memory_2005.py
+++ b/tests/project/test_pypy_worker_memory_2005.py
@@ -9,6 +9,10 @@
 own script with a stub ``python``, as
 :mod:`tests.project.test_sweeps_on_latest_only_1732` does.
 
+#2600: run whole, ``tests/protocols`` outgrew the runner too, so its
+``internet``, ``application`` and ``misc`` subpackages are shards of their own
+ahead of it, and it takes the remainder.
+
 """
 
 from __future__ import annotations
@@ -33,8 +37,9 @@
 
 #: The ``test`` job's KTLO twin, which runs its steps by YAML alias.
 KTLO = ('unit-tests.yml', 'test-ktlo')
-#: The directories a PyPy leg runs on their own, in order.
-SHARDS = ['tests/protocols', 'tests/corekit']
+#: The directories a PyPy leg runs on their own, in order; #2600 split ``tests/protocols``.
+SHARDS = ['tests/protocols/internet', 'tests/protocols/application', 'tests/protocols/misc', 'tests/protocols',
+          'tests/corekit']
 #: The page that says how the legs run.
 DOC = ROOT / 'docs' / 'source' / 'contributing' / 'workflows.rst'
 
@@ -61,10 +66,13 @@ def test_the_ktlo_twin_runs_the_same_step(self) -> None:
         self.assertEqual(job(*KTLO)['steps'], job(*JOB)['steps'])
 
     def test_each_shard_is_a_directory_the_tier_keeps(self) -> None:
-        for shard in SHARDS:
+        """#2600: and each keeps unit-tier modules no earlier shard took, so its run collects a test."""
+        for index, shard in enumerate(SHARDS):
             with self.subTest(shard=shard):
                 self.assertTrue((ROOT / shard).is_dir())
-                self.assertTrue([module for module in _tiers.all_tier_paths() if module.startswith(shard + '/')])
+                earlier = tuple(taken + '/' for taken in SHARDS[:index])
+                self.assertTrue([module for module in _tiers.all_tier_paths() if module.startswith(shard + '/')
+                                 and not module.startswith(earlier) and _tiers.is_unit_tier(module)])
 
 
 @unittest.skipIf(shutil.which('bash') is None, 'the step is a bash script')