Trac #31395: eliminate the --memlimit option to the doctest runner.

Testing is currently impossible on Gentoo because the default memory
limit imposed by the doctest runner is too low for sage to function.
Rather than increase the limit once again, this commit removes the
memory limit entirely. This is not as huge of a change as it seems,
and the choice was made for three reasons:

  * Having a default limit occasionally breaks all testing on some
    platforms and requires the limit to be increased manually.

  * Setting a limit only works reliably on Linux where there are
    easier, more standard ways to set one (like ulimit -v).

  * There's only one test in the sage library that requires a memory
    limit to be set, and having one global memory limit would probably
    not be the correct approach if more tests requiring one were
    added.

This commit removes the --memlimit option, the corresponding code to
set a soft limit, and the support for the "optional - memlimit"
tag. The default memory limit was also thereby eliminated.  The one
test that requires a memory limit was refactored to set its own memory
limit on linux.

This reintroduces some boilerplate to the lone test that requires a
memory limit, but eliminates a recurring problem (the default limit
being too low) in the doctest runner at large. In the future, the
memory limit in that one test may need to be updated, but the absence
of a global limit should allow the doctest runner to function normally
up until that point.

Author: orlitzky

src/bin/sage-runtests

@@ -43,11 +43,6 @@ if __name__ == "__main__":
         callback=optional_argument, callback_args=(int, 0), nargs=0,
         metavar="N", help="tests in parallel using N threads with 0 interpreted as max(2, min(8, cpu_count()))")
     parser.add_option("-T", "--timeout", type=int, default=-1, help="timeout (in seconds) for doctesting one file, 0 for no timeout")
-    parser.add_option("-m", "--memlimit", type=int, default=3300,
-                      help='maximum virtual memory to allow each test '
-                           'process, in megabytes; no limit if zero or less, '
-                           'but tests tagged "optional - memlimit" are '
-                           'skipped if no limit is set (default: 3300 MB)')
     parser.add_option("-a", "--all", action="store_true", default=False, help="test all files in the Sage library")
     parser.add_option("--logfile", metavar="FILE", help="log all output to FILE")
 
@@ -135,39 +130,6 @@ if __name__ == "__main__":
         parser.print_help()
         sys.exit(2)
 
-    # Ensure that all doctests can be run with virtual memory limited to 3300
-    # MiB (or a user-provided value). We must set this limit before starting
-    # Sage. Note that this is a per-process limit, so we do not need to worry
-    # about running multiple doctest processes in parallel. It is in
-    # particular doctests in src/sage/schemes/elliptic_curves/heegner.py
-    # which need this much memory.
-    memlimit = options.memlimit << 20
-
-    # Python's resource module only supports limits up to sys.maxsize,
-    # even if the OS does support higher limits.
-    if 0 < memlimit <= sys.maxsize:
-        import resource
-        lim, hard = resource.getrlimit(resource.RLIMIT_AS)
-        if lim == resource.RLIM_INFINITY or lim > memlimit:
-            try:
-                resource.setrlimit(resource.RLIMIT_AS, (memlimit, hard))
-            except ValueError:
-                options.memlimit = -1
-                if sys.platform != 'cygwin':
-                    # RLIMIT_AS is not currently supported on Cygwin so
-                    # this will probably fail there:
-                    # https://trac.sagemath.org/ticket/23979
-                    raise
-            else:
-                if resource.RLIMIT_AS == getattr(resource, 'RLIMIT_RSS', None):
-                    # On some platforms (e.g. OSX) RLIMIT_AS is just an alias
-                    # for RLIMIT_RSS (see
-                    # https://trac.sagemath.org/ticket/24190)
-                    # In this case we still call setrlimit, but then disable
-                    # high mem tests since we don't want such tests to actually
-                    # cause us to run out of physical memory, leading to system
-                    # instability (as opposed to virtual memory allocs failing)
-                    options.memlimit = -1
     # Limit the number of threads to 2 to save system resources.
     # See Trac #23713, #23892, #30351
     if sys.platform == 'darwin':  

src/sage/doctest/control.py

@@ -96,7 +96,6 @@ def __init__(self, **kwds):
         self.nthreads = 1
         self.serial = False
         self.timeout = -1
-        self.memlimit = 0
         self.all = False
         self.logfile = None
         self.long = False
@@ -381,10 +380,6 @@ def __init__(self, options, args):
 
         self.options = options
 
-        if options.memlimit > 0:
-            # Allow tests that require a virtual memory limit to be set
-            options.optional.add('memlimit')
-
         self.files = args
         if options.logfile:
             try:
@@ -1013,7 +1008,7 @@ def _assemble_cmd(self):
         for o in ("all", "long", "force_lib", "verbose", "failed", "new"):
             if o in opt:
                 cmd += "--%s "%o
-        for o in ("timeout", "memlimit", "randorder", "stats_path"):
+        for o in ("timeout", "randorder", "stats_path"):
             if o in opt:
                 cmd += "--%s=%s "%(o, opt[o])
         if "optional" in opt:

src/sage/doctest/reporting.py

@@ -488,10 +488,6 @@ def report(self, source, timeout, return_code, results, output, pid=None):
                             if not self.controller.options.long:
                                 if self.controller.options.show_skipped:
                                     log("    %s not run"%(count_noun(nskipped, "long test")))
-                        elif tag == "memlimit":
-                            if self.controller.options.memlimit <= 0:
-                                seen_other = True
-                                log("    %s not run"%(count_noun(nskipped, "memlimit")))
                         elif tag == "not tested":
                             if self.controller.options.show_skipped:
                                 log("    %s not run"%(count_noun(nskipped, "not tested test")))

src/sage/doctest/test.py

@@ -511,20 +511,6 @@
     ....: except OSError:
     ....:     pass
 
-Test the ``--memlimit`` option and ``# optional - memlimit``
-(but only on Linux). If this test fails, the memory needed to
-run it may have increased. Try increasing the limit. ::
-
-    sage: from platform import system
-    sage: ok = True
-    sage: from sage.cpython.string import bytes_to_str
-    sage: if system() == "Linux":
-    ....:     P = subprocess.Popen(["sage", "-t", "--warn-long", "0", "--random-seed=0", "--memlimit=2000", "memlimit.rst"], stdout=subprocess.PIPE, **kwds)
-    ....:     out, err = P.communicate()
-    ....:     ok = ("MemoryError: failed to allocate" in bytes_to_str(out))
-    sage: ok or out
-    True
-
 Test that random tests are reproducible::
 
     sage: subprocess.call(["sage", "-t", "--warn-long", "0", "--random-seed=0", "random_seed.rst"], **kwds)  # long time
@@ -558,5 +544,4 @@
     ----------------------------------------------------------------------
     ...
     0
-
 """

src/sage/doctest/tests/memlimit.rst

@@ -168,10 +168,6 @@ cdef class Matrix_mod2_dense(matrix_dense.Matrix_dense):   # dense or sparse
 
         Large matrices fail gracefully::
 
-            sage: MatrixSpace(GF(2), 2^30)(1)  # optional - memlimit
-            Traceback (most recent call last):
-            ...
-            RuntimeError: matrix allocation failed
             sage: MatrixSpace(GF(2), 1, 2^40).zero()
             Traceback (most recent call last):
             ...
@@ -180,6 +176,26 @@ cdef class Matrix_mod2_dense(matrix_dense.Matrix_dense):   # dense or sparse
             Traceback (most recent call last):
             ...
             OverflowError: ...
+
+        Allocation fails if a memory limit is set (Linux only) lower
+        than is needed to construct a matrix but still high enough
+        that it doesn't crash the rest of SageMath::
+
+            sage: from platform import system
+            sage: import resource
+            sage: orig_soft, orig_hard = resource.getrlimit(resource.RLIMIT_AS)
+            sage: if system() != "Linux":
+            ....:     raise RuntimeError("matrix allocation failed")
+            ....: else:
+            ....:     four_GiB = 4*1024^3
+            ....:     resource.setrlimit(resource.RLIMIT_AS, (four_GiB, orig_hard))
+            ....:     MatrixSpace(GF(2), 2^30)(1)
+            Traceback (most recent call last):
+            ...
+            RuntimeError: matrix allocation failed
+            sage: resource.setrlimit(resource.RLIMIT_AS, (orig_soft, orig_hard))
+            sage: (orig_soft, orig_hard) == resource.getrlimit(resource.RLIMIT_AS)
+            True
         """
         # m4ri assumes that nrows and ncols are of type rci_t:
         # check for overflow