From e4c2b30ce8e600e2bf5f6d3e6b95c4dd27abcac4 Mon Sep 17 00:00:00 2001
From: Kubilay Kocak <koobs@FreeBSD.org>
Date: Fri, 29 Nov 2019 10:55:00 +0000
Subject: lang/python{27,35,36,37,38}: Add closefrom(2) support

A single close(fd) syscall is cheap, but when MAXFDS (maximum file
descriptor number) is high, the loop calling close(fd) on each file
descriptor can take several milliseconds.

The default value of subprocess.Popen "close_fds" parameter changed to True
in Python 3. Compared to Python 2, close_fds=True can make Popen 10x
slower: see bpo-37790 [1]

The present workaround on FreeBSD to improve performance is to load and
mount the fdescfs kernel module, but this is not enabled by default.

This change adds minimum viable (and upstreamable) closefrom(2) syscall
support to Python's subprocess and posix modules, improving performance
significantly for loads that involve working with many processes, such as
diffoscope, ansible, and many others.

For additional optimizations, upstream recently (3.8) landed posix_spawn(2)
support [3] and has stated that they will adopt close_range(2) after Linux
merges it [4]. Linux/FreeBSD developers are already collaborating on
ensuring compatible implementations, with FreeBSD's implementation pending
in D21627. [5]

Thank you emaste, cem, kevans for providing analysis, input,
clarifications, comms/upstream support and patches.

[1] https://bugs.python.org/issue37790
[2] https://bugs.python.org/issue38061
[3] https://bugs.python.org/issue35537
[4] https://lwn.net/Articles/789023/
[5] https://reviews.freebsd.org/D21627

Additional References:

https://bugs.python.org/issue8052
https://bugs.python.org/issue11284
https://bugs.python.org/issue13788
https://bugs.python.org/issue1663329
https://www.python.org/dev/peps/pep-0446/

PR:		242274, 221700
Submitted by:	kevans (emaste, cem)
Approved by:	koobs (python (maintainer), santa)
---
 .../files/patch-Modules___posixsubprocess.c        | 25 +++++++++++++++++++++
 lang/python38/files/patch-Modules_posixmodule.c    | 26 ++++++++++++++++++++++
 2 files changed, 51 insertions(+)
 create mode 100644 lang/python38/files/patch-Modules___posixsubprocess.c
 create mode 100644 lang/python38/files/patch-Modules_posixmodule.c

(limited to 'lang/python38/files')

diff --git a/lang/python38/files/patch-Modules___posixsubprocess.c b/lang/python38/files/patch-Modules___posixsubprocess.c
new file mode 100644
index 000000000000..a7c4e43e81cf
--- /dev/null
+++ b/lang/python38/files/patch-Modules___posixsubprocess.c
@@ -0,0 +1,25 @@
+# Add closefrom(2) support
+# https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=242274
+# https://bugs.python.org/issue38061
+# TODO: Upstream
+
+--- Modules/_posixsubprocess.c.orig	2019-10-14 13:34:47 UTC
++++ Modules/_posixsubprocess.c
+@@ -236,8 +236,15 @@ _close_fds_by_brute_force(long start_fd, PyObject *py_
+         start_fd = keep_fd + 1;
+     }
+     if (start_fd <= end_fd) {
+-        for (fd_num = start_fd; fd_num < end_fd; ++fd_num) {
+-            close(fd_num);
++#if defined(__FreeBSD__)
++        if (end_fd >= sysconf(_SC_OPEN_MAX)) {
++            closefrom(start_fd);
++        } else
++#endif
++        {
++            for (fd_num = start_fd; fd_num < end_fd; ++fd_num) {
++                close(fd_num);
++            }
+         }
+     }
+ }
diff --git a/lang/python38/files/patch-Modules_posixmodule.c b/lang/python38/files/patch-Modules_posixmodule.c
new file mode 100644
index 000000000000..441c78f81016
--- /dev/null
+++ b/lang/python38/files/patch-Modules_posixmodule.c
@@ -0,0 +1,26 @@
+# Add closefrom(2) support
+# https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=242274
+# https://bugs.python.org/issue38061
+# TODO: Upstream
+
+--- Modules/posixmodule.c.orig	2019-10-14 13:34:47 UTC
++++ Modules/posixmodule.c
+@@ -8460,8 +8460,16 @@ os_closerange_impl(PyObject *module, int fd_low, int f
+     lohi[1] = fd_high;
+     fdwalk(_fdwalk_close_func, lohi);
+ #else
+-    for (i = Py_MAX(fd_low, 0); i < fd_high; i++)
+-        close(i);
++    fd_low = Py_MAX(fd_low, 0);
++#ifdef __FreeBSD__
++    if (fd_high >= sysconf(_SC_OPEN_MAX)) {
++        closefrom(fd_low);
++    } else
++#endif
++    {
++        for (i = fd_low; i < fd_high; i++)
++            close(i);
++    }
+ #endif
+     _Py_END_SUPPRESS_IPH
+     Py_END_ALLOW_THREADS
-- 
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