From e1e9680dd7e405cbfad80ea358d6352a9ef80873 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Adrian=20W=C3=A4lchli?= <aedu.waelchli@gmail.com>
Date: Thu, 18 Jun 2020 23:50:23 +0200
Subject: [PATCH 01/14] support sanity_val_step=-1

---
 pytorch_lightning/trainer/trainer.py | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/pytorch_lightning/trainer/trainer.py b/pytorch_lightning/trainer/trainer.py
index d1601caba9392..166a479499964 100644
--- a/pytorch_lightning/trainer/trainer.py
+++ b/pytorch_lightning/trainer/trainer.py
@@ -1061,7 +1061,7 @@ def run_pretrain_routine(self, model: LightningModule):
 
         # run tiny validation (if validation defined)
         # to make sure program won't crash during val
-        if not self.disable_validation and self.num_sanity_val_steps > 0:
+        if not self.disable_validation and self.num_sanity_val_steps:
             self.reset_val_dataloader(ref_model)
 
             # hook and callback
@@ -1070,6 +1070,7 @@ def run_pretrain_routine(self, model: LightningModule):
 
             num_loaders = len(self.val_dataloaders)
             max_batches = [self.num_sanity_val_steps] * num_loaders
+            max_batches = [float('inf') for m in max_batches if m == -1]
             eval_results = self._evaluate(model,
                                           self.val_dataloaders,
                                           max_batches,

From d375e2adc5906a41a7a2a9ed76f03f7a4d2d2681 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Adrian=20W=C3=A4lchli?= <aedu.waelchli@gmail.com>
Date: Sat, 20 Jun 2020 12:13:40 +0200
Subject: [PATCH 02/14] fix list size

---
 pytorch_lightning/trainer/trainer.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/pytorch_lightning/trainer/trainer.py b/pytorch_lightning/trainer/trainer.py
index 166a479499964..6e789f2a12aa5 100644
--- a/pytorch_lightning/trainer/trainer.py
+++ b/pytorch_lightning/trainer/trainer.py
@@ -1070,7 +1070,7 @@ def run_pretrain_routine(self, model: LightningModule):
 
             num_loaders = len(self.val_dataloaders)
             max_batches = [self.num_sanity_val_steps] * num_loaders
-            max_batches = [float('inf') for m in max_batches if m == -1]
+            max_batches = [float('inf') if m == -1 else m for m in max_batches]
             eval_results = self._evaluate(model,
                                           self.val_dataloaders,
                                           max_batches,

From 0be420c1577c33c3ca81f9ef6cc12122dce39fbb Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Adrian=20W=C3=A4lchli?= <aedu.waelchli@gmail.com>
Date: Sat, 20 Jun 2020 12:21:28 +0200
Subject: [PATCH 03/14] simplification

---
 pytorch_lightning/trainer/trainer.py | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/pytorch_lightning/trainer/trainer.py b/pytorch_lightning/trainer/trainer.py
index 6e789f2a12aa5..7170c64a89b1b 100644
--- a/pytorch_lightning/trainer/trainer.py
+++ b/pytorch_lightning/trainer/trainer.py
@@ -379,7 +379,7 @@ def __init__(
         self.max_steps = max_steps
         self.min_steps = min_steps
 
-        self.num_sanity_val_steps = num_sanity_val_steps
+        self.num_sanity_val_steps = float("inf") if num_sanity_val_steps == -1 else num_sanity_val_steps
         # Backward compatibility, TODO: remove in v0.9.0
         if print_nan_grads:
             rank_zero_warn("Argument `print_nan_grads` has no effect and will be removed in v0.9.0."
@@ -1070,7 +1070,6 @@ def run_pretrain_routine(self, model: LightningModule):
 
             num_loaders = len(self.val_dataloaders)
             max_batches = [self.num_sanity_val_steps] * num_loaders
-            max_batches = [float('inf') if m == -1 else m for m in max_batches]
             eval_results = self._evaluate(model,
                                           self.val_dataloaders,
                                           max_batches,

From 66f4e9157230d4454578a238ddd007d994a4c081 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Adrian=20W=C3=A4lchli?= <aedu.waelchli@gmail.com>
Date: Sat, 20 Jun 2020 12:22:30 +0200
Subject: [PATCH 04/14] simplify

---
 pytorch_lightning/trainer/trainer.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/pytorch_lightning/trainer/trainer.py b/pytorch_lightning/trainer/trainer.py
index 7170c64a89b1b..131e8c893b6cf 100644
--- a/pytorch_lightning/trainer/trainer.py
+++ b/pytorch_lightning/trainer/trainer.py
@@ -1061,7 +1061,7 @@ def run_pretrain_routine(self, model: LightningModule):
 
         # run tiny validation (if validation defined)
         # to make sure program won't crash during val
-        if not self.disable_validation and self.num_sanity_val_steps:
+        if not self.disable_validation and self.num_sanity_val_steps > 0:
             self.reset_val_dataloader(ref_model)
 
             # hook and callback

From d7b56e9aa7eacf93e10794891c7794464eb7b057 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Adrian=20W=C3=A4lchli?= <aedu.waelchli@gmail.com>
Date: Mon, 22 Jun 2020 23:01:52 +0200
Subject: [PATCH 05/14] add test for num_sanity_val_steps=-1

---
 pytorch_lightning/callbacks/progress.py |  2 +-
 tests/trainer/test_trainer.py           | 19 +++++++++++++++++++
 2 files changed, 20 insertions(+), 1 deletion(-)

diff --git a/pytorch_lightning/callbacks/progress.py b/pytorch_lightning/callbacks/progress.py
index 358575273f945..4ea9ea1c91b4f 100644
--- a/pytorch_lightning/callbacks/progress.py
+++ b/pytorch_lightning/callbacks/progress.py
@@ -295,7 +295,7 @@ def init_test_tqdm(self) -> tqdm:
     def on_sanity_check_start(self, trainer, pl_module):
         super().on_sanity_check_start(trainer, pl_module)
         self.val_progress_bar = self.init_sanity_tqdm()
-        self.val_progress_bar.total = trainer.num_sanity_val_steps * len(trainer.val_dataloaders)
+        self.val_progress_bar.total = convert_inf(trainer.num_sanity_val_steps * len(trainer.val_dataloaders))
         self.main_progress_bar = tqdm(disable=True)  # dummy progress bar
 
     def on_sanity_check_end(self, trainer, pl_module):
diff --git a/tests/trainer/test_trainer.py b/tests/trainer/test_trainer.py
index 5e4cf3544e911..39cca94711aa0 100644
--- a/tests/trainer/test_trainer.py
+++ b/tests/trainer/test_trainer.py
@@ -6,6 +6,7 @@
 import types
 from argparse import Namespace
 from pathlib import Path
+from unittest.mock import patch
 
 import cloudpickle
 import pytest
@@ -782,6 +783,24 @@ def test_gpu_choice(tmpdir):
         Trainer(**trainer_options, gpus=num_gpus + 1, auto_select_gpus=True)
 
 
+
+def test_num_sanity_val_steps(tmpdir):
+    model = EvalModelTemplate()
+    trainer = Trainer(
+        num_sanity_val_steps=-1,
+        # TODO: limit_val_batches influences num_sanity_val_step. Fix it.
+        # limit_val_batches=0,
+        max_steps=1,
+        default_root_dir=tmpdir
+    )
+    assert trainer.num_sanity_val_steps == float('inf')
+    val_dataloader = model.val_dataloader()
+
+    with patch.object(trainer, 'evaluation_forward', wraps=trainer.evaluation_forward) as mocked:
+        trainer.fit(model, val_dataloaders=val_dataloader)
+        assert mocked.call_count == len(val_dataloader)
+
+
 @pytest.mark.parametrize("trainer_kwargs,expected", [
     pytest.param(
         dict(distributed_backend=None, gpus=None),

From bd47b70093fab19d55a0476e59f0867f49e8eade Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Adrian=20W=C3=A4lchli?= <aedu.waelchli@gmail.com>
Date: Mon, 22 Jun 2020 23:05:35 +0200
Subject: [PATCH 06/14] update test

---
 tests/trainer/test_trainer.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tests/trainer/test_trainer.py b/tests/trainer/test_trainer.py
index 39cca94711aa0..3da84282eee9e 100644
--- a/tests/trainer/test_trainer.py
+++ b/tests/trainer/test_trainer.py
@@ -783,8 +783,8 @@ def test_gpu_choice(tmpdir):
         Trainer(**trainer_options, gpus=num_gpus + 1, auto_select_gpus=True)
 
 
-
 def test_num_sanity_val_steps(tmpdir):
+    """ Test that num_sanity_val_steps=-1 runs through all validation data once. """
     model = EvalModelTemplate()
     trainer = Trainer(
         num_sanity_val_steps=-1,

From dd3862d4da07d748cef1dd2aca39f080e4280ed5 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Adrian=20W=C3=A4lchli?= <aedu.waelchli@gmail.com>
Date: Tue, 23 Jun 2020 00:04:13 +0200
Subject: [PATCH 07/14] update docs

---
 docs/source/debugging.rst                    | 2 +-
 pytorch_lightning/trainer/__init__.py        | 7 +++++--
 pytorch_lightning/trainer/evaluation_loop.py | 7 ++++---
 pytorch_lightning/trainer/trainer.py         | 3 ++-
 4 files changed, 12 insertions(+), 7 deletions(-)

diff --git a/docs/source/debugging.rst b/docs/source/debugging.rst
index 06f9cd4344b43..0339cc6a98e7d 100644
--- a/docs/source/debugging.rst
+++ b/docs/source/debugging.rst
@@ -129,4 +129,4 @@ argument of :class:`~pytorch_lightning.trainer.trainer.Trainer`)
 .. testcode::
 
     # DEFAULT
-    trainer = Trainer(num_sanity_val_steps=5)
\ No newline at end of file
+    trainer = Trainer(num_sanity_val_steps=2)
\ No newline at end of file
diff --git a/pytorch_lightning/trainer/__init__.py b/pytorch_lightning/trainer/__init__.py
index 074fd29650642..e56d4df7e21ef 100644
--- a/pytorch_lightning/trainer/__init__.py
+++ b/pytorch_lightning/trainer/__init__.py
@@ -599,16 +599,19 @@ def on_train_end(self, trainer, pl_module):
 
 Sanity check runs n batches of val before starting the training routine.
 This catches any bugs in your validation without having to wait for the first validation check.
-The Trainer uses 5 steps by default. Turn it off or modify it here.
+The Trainer uses 2 steps by default. Turn it off or modify it here.
 
 .. testcode::
 
     # default used by the Trainer
-    trainer = Trainer(num_sanity_val_steps=5)
+    trainer = Trainer(num_sanity_val_steps=2)
 
     # turn it off
     trainer = Trainer(num_sanity_val_steps=0)
 
+    # check all validation data
+    trainer = Trainer(num_sanity_val_steps=-1)
+
 num_tpu_cores
 ^^^^^^^^^^^^^
 .. warning:: .. deprecated:: 0.7.6
diff --git a/pytorch_lightning/trainer/evaluation_loop.py b/pytorch_lightning/trainer/evaluation_loop.py
index 230538ed89c01..dfd73efbb10d8 100644
--- a/pytorch_lightning/trainer/evaluation_loop.py
+++ b/pytorch_lightning/trainer/evaluation_loop.py
@@ -72,15 +72,16 @@
 -----------------------------------------
 
 Lightning runs a few steps of validation in the beginning of training.
- This avoids crashing in the validation loop sometime deep into a lengthy training loop.
+This avoids crashing in the validation loop sometime deep into a lengthy training loop.
 
 .. code-block:: python
 
     # DEFAULT
-    trainer = Trainer(num_sanity_val_steps=5)
+    trainer = Trainer(num_sanity_val_steps=2)
 
 
-You can use `Trainer(num_sanity_val_steps=0)` to skip the sanity check.
+You can use `Trainer(num_sanity_val_steps=0)` to skip the sanity check or `Trainer(num_sanity_val_steps=-1)`
+to check all the validation data.
 
 # Testing loop
 
diff --git a/pytorch_lightning/trainer/trainer.py b/pytorch_lightning/trainer/trainer.py
index 131e8c893b6cf..e59e97315b02b 100644
--- a/pytorch_lightning/trainer/trainer.py
+++ b/pytorch_lightning/trainer/trainer.py
@@ -278,7 +278,8 @@ def __init__(
 
             amp_level: The optimization level to use (O1, O2, etc...).
 
-            num_sanity_val_steps: Sanity check runs n batches of val before starting the training routine.
+            num_sanity_val_steps: Sanity check runs n validation batches before starting the training routine.
+                Set it to `-1` to run all batches in all validation dataloaders. Default: 2
 
             truncated_bptt_steps: Truncated back prop breaks performs backprop every k steps of
 

From a15fd8de22d80f7c886f0dd9718f17f933984756 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Adrian=20W=C3=A4lchli?= <aedu.waelchli@gmail.com>
Date: Tue, 23 Jun 2020 00:14:55 +0200
Subject: [PATCH 08/14] extend tests to multiple dataloaders

---
 tests/trainer/test_trainer.py | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/tests/trainer/test_trainer.py b/tests/trainer/test_trainer.py
index 3da84282eee9e..6ad582121707b 100644
--- a/tests/trainer/test_trainer.py
+++ b/tests/trainer/test_trainer.py
@@ -794,11 +794,11 @@ def test_num_sanity_val_steps(tmpdir):
         default_root_dir=tmpdir
     )
     assert trainer.num_sanity_val_steps == float('inf')
-    val_dataloader = model.val_dataloader()
+    val_dataloaders = model.val_dataloader__multiple()
 
     with patch.object(trainer, 'evaluation_forward', wraps=trainer.evaluation_forward) as mocked:
-        trainer.fit(model, val_dataloaders=val_dataloader)
-        assert mocked.call_count == len(val_dataloader)
+        trainer.fit(model, val_dataloaders=val_dataloaders)
+        assert mocked.call_count == sum(len(dl) for dl in val_dataloaders)
 
 
 @pytest.mark.parametrize("trainer_kwargs,expected", [

From cef85c3fec3e083582beeee6cb37ae4cfd851226 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Adrian=20W=C3=A4lchli?= <aedu.waelchli@gmail.com>
Date: Tue, 23 Jun 2020 00:21:00 +0200
Subject: [PATCH 09/14] changelog

---
 CHANGELOG.md | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 51e56e7c1b18b..bff49dc337d32 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -8,6 +8,8 @@ The format is based on [Keep a Changelog](http://keepachangelog.com/en/1.0.0/).
 
 ### Added
 
+- Added support for `Trainer(num_sanity_val_steps=-1)` to check all validation data before training ([#2246](https://github.com/PyTorchLightning/pytorch-lightning/pull/2246))
+
 ### Changed
 
 - Changed epoch indexing from 0 instead of 1 ([#2289](https://github.com/PyTorchLightning/pytorch-lightning/pull/2289))

From e7c2a8d505312db41fe8d2e9ae5e6945f6684364 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Adrian=20W=C3=A4lchli?= <aedu.waelchli@gmail.com>
Date: Sat, 27 Jun 2020 01:14:16 +0200
Subject: [PATCH 10/14] Update tests/trainer/test_trainer.py

Co-authored-by: Jirka Borovec <Borda@users.noreply.github.com>
---
 tests/trainer/test_trainer.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tests/trainer/test_trainer.py b/tests/trainer/test_trainer.py
index 30455537ac5ed..33565ab79c74f 100644
--- a/tests/trainer/test_trainer.py
+++ b/tests/trainer/test_trainer.py
@@ -813,7 +813,7 @@ def test_num_sanity_val_steps(tmpdir):
         # TODO: limit_val_batches influences num_sanity_val_step. Fix it.
         # limit_val_batches=0,
         max_steps=1,
-        default_root_dir=tmpdir
+        default_root_dir=tmpdir,
     )
     assert trainer.num_sanity_val_steps == float('inf')
     val_dataloaders = model.val_dataloader__multiple()

From 231c0c6be4e4b28f7992cd216855742681f491b0 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Adrian=20W=C3=A4lchli?= <aedu.waelchli@gmail.com>
Date: Mon, 29 Jun 2020 23:32:51 +0200
Subject: [PATCH 11/14] improve test

---
 tests/trainer/test_trainer.py | 20 +++++++++++++++-----
 1 file changed, 15 insertions(+), 5 deletions(-)

diff --git a/tests/trainer/test_trainer.py b/tests/trainer/test_trainer.py
index 7b147917dc55a..8f9c88744dc96 100644
--- a/tests/trainer/test_trainer.py
+++ b/tests/trainer/test_trainer.py
@@ -809,15 +809,25 @@ def test_tpu_choice(tmpdir, tpu_cores, expected_tpu_id, error_expected):
         assert trainer.tpu_id == expected_tpu_id
 
 
-def test_num_sanity_val_steps(tmpdir):
-    """ Test that num_sanity_val_steps=-1 runs through all validation data once. """
+@pytest.mark.parametrize(['limit_val_batches'], [
+    pytest.param(0.0),
+    pytest.param(1),
+    pytest.param(1.0),
+    pytest.param(0.3),
+])
+def test_num_sanity_val_steps(tmpdir, limit_val_batches):
+    """
+    Test that num_sanity_val_steps=-1 runs through all validation data once.
+    Makes sure this setting is independent of limit_val_batches.
+    """
     model = EvalModelTemplate()
+    model.validation_step = model.validation_step__multiple_dataloaders
+    model.validation_epoch_end = model.validation_epoch_end__multiple_dataloaders
     trainer = Trainer(
+        default_root_dir=tmpdir,
         num_sanity_val_steps=-1,
-        # TODO: limit_val_batches influences num_sanity_val_step. Fix it.
-        # limit_val_batches=0,
+        limit_val_batches=limit_val_batches,  # should have no influence
         max_steps=1,
-        default_root_dir=tmpdir,
     )
     assert trainer.num_sanity_val_steps == float('inf')
     val_dataloaders = model.val_dataloader__multiple()

From 6dc3d8bd97a89149be4847e1201e41290df7e786 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Adrian=20W=C3=A4lchli?= <aedu.waelchli@gmail.com>
Date: Tue, 30 Jun 2020 00:04:40 +0200
Subject: [PATCH 12/14] refactor the sanity check decision

---
 pytorch_lightning/callbacks/progress.py    |  2 +-
 pytorch_lightning/trainer/trainer.py       | 20 +++++++++++++++-----
 pytorch_lightning/trainer/training_loop.py |  2 +-
 tests/trainer/test_trainer.py              |  4 ++--
 4 files changed, 19 insertions(+), 9 deletions(-)

diff --git a/pytorch_lightning/callbacks/progress.py b/pytorch_lightning/callbacks/progress.py
index 4ea9ea1c91b4f..935670be1240e 100644
--- a/pytorch_lightning/callbacks/progress.py
+++ b/pytorch_lightning/callbacks/progress.py
@@ -95,7 +95,7 @@ def total_val_batches(self) -> int:
         total_val_batches = 0
         if trainer.fast_dev_run and trainer.val_dataloaders is not None:
             total_val_batches = len(trainer.val_dataloaders)
-        elif not self.trainer.disable_validation:
+        elif self.trainer.enable_validation:
             is_val_epoch = (trainer.current_epoch + 1) % trainer.check_val_every_n_epoch == 0
             total_val_batches = sum(trainer.num_val_batches) if is_val_epoch else 0
         return total_val_batches
diff --git a/pytorch_lightning/trainer/trainer.py b/pytorch_lightning/trainer/trainer.py
index cc77748903c89..50cf583509fc4 100644
--- a/pytorch_lightning/trainer/trainer.py
+++ b/pytorch_lightning/trainer/trainer.py
@@ -345,7 +345,6 @@ def __init__(
         # training state
         self.model = None
         self.testing = False
-        self.disable_validation = False
         self.prepare_data_per_node = prepare_data_per_node
         self.lr_schedulers = []
         self.optimizers = None
@@ -798,6 +797,18 @@ def progress_bar_dict(self) -> dict:
         ref_model = self.model if not self.data_parallel else self.model.module
         return dict(**ref_model.get_progress_bar_dict(), **self.progress_bar_metrics)
 
+    @property
+    def disable_validation(self) -> bool:
+        """ Check if validation is disabled during training. """
+        disable_validation = not (self.is_overridden('validation_step') and self.limit_val_batches > 0) \
+            and not self.fast_dev_run
+        return disable_validation
+
+    @property
+    def enable_validation(self) -> bool:
+        """ Check if we should run validation during training. """
+        return not self.disable_validation
+
     # -----------------------------
     # MODEL TRAINING
     # -----------------------------
@@ -1066,13 +1077,12 @@ def run_pretrain_routine(self, model: LightningModule):
             self.run_evaluation(test_mode=True)
             return
 
-        # check if we should run validation during training
-        self.disable_validation = not (self.is_overridden('validation_step') and self.limit_val_batches > 0) \
-            and not self.fast_dev_run
+        should_sanity_check = self.is_overridden('validation_step') and self.num_sanity_val_steps > 0 \
+            and self.limit_val_batches > 0
 
         # run tiny validation (if validation defined)
         # to make sure program won't crash during val
-        if not self.disable_validation and self.num_sanity_val_steps > 0:
+        if should_sanity_check:
             self.reset_val_dataloader(ref_model)
 
             # hook and callback
diff --git a/pytorch_lightning/trainer/training_loop.py b/pytorch_lightning/trainer/training_loop.py
index 1f6a36eb56c89..3d667b9a88f3a 100644
--- a/pytorch_lightning/trainer/training_loop.py
+++ b/pytorch_lightning/trainer/training_loop.py
@@ -569,7 +569,7 @@ def should_check_val(self, batch_idx, is_last_batch):
         # decide if we should run validation
         is_val_check_batch = (batch_idx + 1) % self.val_check_batch == 0
         can_check_epoch = (self.current_epoch + 1) % self.check_val_every_n_epoch == 0
-        can_check_val = not self.disable_validation and can_check_epoch
+        can_check_val = self.enable_validation and can_check_epoch
         should_check_val = is_val_check_batch or self.should_stop
         is_last_batch_for_infinite_dataset = (is_last_batch and self.val_check_batch == float('inf'))
         should_check_val = can_check_val and (should_check_val or is_last_batch_for_infinite_dataset)
diff --git a/tests/trainer/test_trainer.py b/tests/trainer/test_trainer.py
index 8f9c88744dc96..d928b88811c8f 100644
--- a/tests/trainer/test_trainer.py
+++ b/tests/trainer/test_trainer.py
@@ -810,7 +810,7 @@ def test_tpu_choice(tmpdir, tpu_cores, expected_tpu_id, error_expected):
 
 
 @pytest.mark.parametrize(['limit_val_batches'], [
-    pytest.param(0.0),
+    pytest.param(0.0),  # this should run no sanity checks
     pytest.param(1),
     pytest.param(1.0),
     pytest.param(0.3),
@@ -834,7 +834,7 @@ def test_num_sanity_val_steps(tmpdir, limit_val_batches):
 
     with patch.object(trainer, 'evaluation_forward', wraps=trainer.evaluation_forward) as mocked:
         trainer.fit(model, val_dataloaders=val_dataloaders)
-        assert mocked.call_count == sum(len(dl) for dl in val_dataloaders)
+        assert mocked.call_count == sum(len(dl) * (limit_val_batches > 0) for dl in val_dataloaders)
 
 
 @pytest.mark.parametrize("trainer_kwargs,expected", [

From 8713ccdd6ee6b0bc245db15133b1b99d5a6da735 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Adrian=20W=C3=A4lchli?= <aedu.waelchli@gmail.com>
Date: Thu, 23 Jul 2020 03:15:01 +0200
Subject: [PATCH 13/14] fix merge

---
 pytorch_lightning/trainer/trainer.py | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/pytorch_lightning/trainer/trainer.py b/pytorch_lightning/trainer/trainer.py
index 810fd55c3dda3..0ee3bf1b69d9a 100644
--- a/pytorch_lightning/trainer/trainer.py
+++ b/pytorch_lightning/trainer/trainer.py
@@ -1198,9 +1198,6 @@ def run_pretrain_routine(self, model: LightningModule):
 
             return eval_loop_results
 
-        should_sanity_check = self.is_overridden('validation_step') and self.num_sanity_val_steps > 0 \
-            and self.limit_val_batches > 0
-
         # run a few val batches before training starts
         self._run_sanity_check(ref_model, model)
 
@@ -1215,6 +1212,9 @@ def run_pretrain_routine(self, model: LightningModule):
         self.train()
 
     def _run_sanity_check(self, ref_model, model):
+        should_sanity_check = self.is_overridden('validation_step') and self.num_sanity_val_steps > 0 \
+            and self.limit_val_batches > 0
+
         # run tiny validation (if validation defined)
         # to make sure program won't crash during val
         if should_sanity_check:

From ed62155634fb6ed53f51c08349055885cea9d673 Mon Sep 17 00:00:00 2001
From: William Falcon <waf2107@columbia.edu>
Date: Thu, 23 Jul 2020 06:47:55 -0400
Subject: [PATCH 14/14] Update trainer.py

---
 pytorch_lightning/trainer/trainer.py | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/pytorch_lightning/trainer/trainer.py b/pytorch_lightning/trainer/trainer.py
index 0ee3bf1b69d9a..bee332f831cce 100644
--- a/pytorch_lightning/trainer/trainer.py
+++ b/pytorch_lightning/trainer/trainer.py
@@ -886,14 +886,13 @@ def progress_bar_dict(self) -> dict:
     @property
     def disable_validation(self) -> bool:
         """ Check if validation is disabled during training. """
-        disable_validation = not (self.is_overridden('validation_step') and self.limit_val_batches > 0) \
-            and not self.fast_dev_run
-        return disable_validation
+        return not self.enable_validation
 
     @property
     def enable_validation(self) -> bool:
         """ Check if we should run validation during training. """
-        return not self.disable_validation
+        val_loop_enabled = (self.is_overridden('validation_step') and self.limit_val_batches > 0)
+        return val_loop_enabled or self.fast_dev_run
 
     # -----------------------------
     # MODEL TRAINING