[modeling utils] revamp from_pretrained(..., low_cpu_mem_usage=True) + tests (#16657)

* add low_cpu_mem_usage tests

* wip: revamping

* wip

* install /usr/bin/time

* wip

* cleanup

* cleanup

* cleanup

* cleanup

* cleanup

* fix assert

* put the wrapper back

* cleanup; switch to bert-base-cased

* Trigger CI

* Trigger CI

src/transformers/testing_utils.py

@@ -17,6 +17,7 @@ import inspect
 import logging
 import os
 import re
+import shlex
 import shutil
 import sys
 import tempfile
@@ -667,6 +668,20 @@ def require_librosa(test_case):
         return test_case
 
 
+def cmd_exists(cmd):
+    return shutil.which(cmd) is not None
+
+
+def require_usr_bin_time(test_case):
+    """
+    Decorator marking a test that requires `/usr/bin/time`
+    """
+    if not cmd_exists("/usr/bin/time"):
+        return unittest.skip("test requires /usr/bin/time")(test_case)
+    else:
+        return test_case
+
+
 def get_gpu_count():
     """
     Return the number of available gpus (regardless of whether torch, tf or jax is used)
@@ -1178,6 +1193,39 @@ class TestCasePlus(unittest.TestCase):
 
         return tmp_dir
 
+    def python_one_liner_max_rss(self, one_liner_str):
+        """
+        Runs the passed python one liner (just the code) and returns how much max cpu memory was used to run the
+        program.
+
+        Args:
+            one_liner_str (`string`):
+                a python one liner code that gets passed to `python -c`
+
+        Returns:
+            max cpu memory bytes used to run the program. This value is likely to vary slightly from run to run.
+
+        Requirements:
+            this helper needs `/usr/bin/time` to be installed (`apt install time`)
+
+        Example:
+
+        ```
+        one_liner_str = 'from transformers import AutoModel; AutoModel.from_pretrained("t5-large")'
+        max_rss = self.python_one_liner_max_rss(one_liner_str)
+        ```
+        """
+
+        if not cmd_exists("/usr/bin/time"):
+            raise ValueError("/usr/bin/time is required, install with `apt install time`")
+
+        cmd = shlex.split(f"/usr/bin/time -f %M python -c '{one_liner_str}'")
+        with CaptureStd() as cs:
+            execute_subprocess_async(cmd, env=self.get_env())
+        # returned data is in KB so convert to bytes
+        max_rss = int(cs.err.split("\n")[-2].replace("stderr: ", "")) * 1024
+        return max_rss
+
     def tearDown(self):
 
         # get_auto_remove_tmp_dir feature: remove registered temp dirs