diff --git a/Lib/test/test_mmap.py b/Lib/test/test_mmap.py
index 309c0d8c933..38ee32db947 100644
--- a/Lib/test/test_mmap.py
+++ b/Lib/test/test_mmap.py
@@ -1,3 +1,4 @@
+from test import support
 from test.support import (
     requires, _2G, _4G, gc_collect, cpython_only, is_emscripten, is_apple,
     in_systemd_nspawn_sync_suppressed,
@@ -5,8 +6,8 @@
 from test.support.import_helper import import_module
 from test.support.os_helper import TESTFN, unlink
 from test.support.script_helper import assert_python_ok
-import unittest
 import errno
+import unittest
 import os
 import re
 import itertools
@@ -58,6 +59,7 @@ def test_basic(self):
             f.write(b'\0'* (PAGESIZE-3) )
             f.flush()
             m = mmap.mmap(f.fileno(), 2 * PAGESIZE)
+            self.addCleanup(m.close)
         finally:
             f.close()
 
@@ -115,31 +117,28 @@ def test_basic(self):
         # Try to seek to negative position...
         self.assertRaises(ValueError, m.seek, -len(m)-1, 2)
 
+    @unittest.skipUnless(hasattr(mmap.mmap, 'resize'), 'requires mmap.resize')
+    def test_resize(self):
+        # Create a file to be mmap'ed.
+        with open(TESTFN, 'bw+') as f:
+            # Write 2 pages worth of data to the file
+            f.write(b'\0'* 2 * PAGESIZE)
+            f.flush()
+            m = mmap.mmap(f.fileno(), 2 * PAGESIZE)
+            self.addCleanup(m.close)
+
         # Try resizing map
-        try:
-            m.resize(512)
-        except SystemError:
-            # resize() not supported
-            # No messages are printed, since the output of this test suite
-            # would then be different across platforms.
-            pass
-        else:
-            # resize() is supported
-            self.assertEqual(len(m), 512)
-            # Check that we can no longer seek beyond the new size.
-            self.assertRaises(ValueError, m.seek, 513, 0)
-
-            # Check that the underlying file is truncated too
-            # (bug #728515)
-            f = open(TESTFN, 'rb')
-            try:
-                f.seek(0, 2)
-                self.assertEqual(f.tell(), 512)
-            finally:
-                f.close()
-            self.assertEqual(m.size(), 512)
+        m.resize(512)
+        self.assertEqual(len(m), 512)
+        # Check that we can no longer seek beyond the new size.
+        self.assertRaises(ValueError, m.seek, 513, 0)
 
-        m.close()
+        # Check that the underlying file is truncated too
+        # (bug #728515)
+        with open(TESTFN, 'rb') as f:
+            f.seek(0, 2)
+            self.assertEqual(f.tell(), 512)
+        self.assertEqual(m.size(), 512)
 
     def test_access_parameter(self):
         # Test for "access" keyword parameter
@@ -184,15 +183,10 @@ def test_access_parameter(self):
             else:
                 self.fail("Able to write to readonly memory map")
 
-            # Ensuring that readonly mmap can't be resized
-            try:
-                m.resize(2*mapsize)
-            except SystemError:   # resize is not universally supported
-                pass
-            except TypeError:
-                pass
-            else:
-                self.fail("Able to resize readonly memory map")
+            if hasattr(m, 'resize'):
+                # Ensuring that readonly mmap can't be resized
+                with self.assertRaises(TypeError):
+                    m.resize(2 * mapsize)
             with open(TESTFN, "rb") as fp:
                 self.assertEqual(fp.read(), b'a'*mapsize,
                                  "Readonly memory map data file was modified")
@@ -243,8 +237,9 @@ def test_access_parameter(self):
             with open(TESTFN, "rb") as fp:
                 self.assertEqual(fp.read(), b'c'*mapsize,
                                  "Copy-on-write test data file should not be modified.")
-            # Ensuring copy-on-write maps cannot be resized
-            self.assertRaises(TypeError, m.resize, 2*mapsize)
+            if hasattr(m, 'resize'):
+                # Ensuring copy-on-write maps cannot be resized
+                self.assertRaises(TypeError, m.resize, 2 * mapsize)
             m.close()
 
         # Ensuring invalid access parameter raises exception
@@ -271,62 +266,57 @@ def test_access_parameter(self):
                     self.assertRaises(TypeError, m.write_byte, 0)
                     m.close()
 
-    @unittest.skipIf(os.name == 'nt', 'trackfd not present on Windows')
-    def test_trackfd_parameter(self):
+    @support.subTests('close_original_fd', (True, False))
+    def test_trackfd_parameter(self, close_original_fd):
         size = 64
         with open(TESTFN, "wb") as f:
             f.write(b"a"*size)
-        for close_original_fd in True, False:
-            with self.subTest(close_original_fd=close_original_fd):
-                with open(TESTFN, "r+b") as f:
-                    with mmap.mmap(f.fileno(), size, trackfd=False) as m:
-                        if close_original_fd:
-                            f.close()
-                        self.assertEqual(len(m), size)
-                        with self.assertRaises(OSError) as err_cm:
-                            m.size()
-                        self.assertEqual(err_cm.exception.errno, errno.EBADF)
-                        with self.assertRaises(ValueError):
-                            m.resize(size * 2)
-                        with self.assertRaises(ValueError):
-                            m.resize(size // 2)
-                        self.assertEqual(m.closed, False)
-
-                        # Smoke-test other API
-                        m.write_byte(ord('X'))
-                        m[2] = ord('Y')
-                        m.flush()
-                        with open(TESTFN, "rb") as f:
-                            self.assertEqual(f.read(4), b'XaYa')
-                        self.assertEqual(m.tell(), 1)
-                        m.seek(0)
-                        self.assertEqual(m.tell(), 0)
-                        self.assertEqual(m.read_byte(), ord('X'))
-
-                self.assertEqual(m.closed, True)
-                self.assertEqual(os.stat(TESTFN).st_size, size)
-
-    @unittest.skipIf(os.name == 'nt', 'trackfd not present on Windows')
+        with open(TESTFN, "r+b") as f:
+            with mmap.mmap(f.fileno(), size, trackfd=False) as m:
+                if close_original_fd:
+                    f.close()
+                self.assertEqual(len(m), size)
+                with self.assertRaises(ValueError):
+                    m.size()
+                if hasattr(m, 'resize'):
+                    with self.assertRaises(ValueError):
+                        m.resize(size * 2)
+                    with self.assertRaises(ValueError):
+                        m.resize(size // 2)
+                self.assertIs(m.closed, False)
+
+                # Smoke-test other API
+                m.write_byte(ord('X'))
+                m[2] = ord('Y')
+                m.flush()
+                with open(TESTFN, "rb") as f:
+                    self.assertEqual(f.read(4), b'XaYa')
+                self.assertEqual(m.tell(), 1)
+                m.seek(0)
+                self.assertEqual(m.tell(), 0)
+                self.assertEqual(m.read_byte(), ord('X'))
+
+                if os.name == 'nt' and not close_original_fd:
+                    self.assertRaises(PermissionError, os.rename, TESTFN, TESTFN+'1')
+                else:
+                    os.rename(TESTFN, TESTFN+'1')
+                    os.rename(TESTFN+'1', TESTFN)
+
+        self.assertIs(m.closed, True)
+        self.assertEqual(os.stat(TESTFN).st_size, size)
+
     def test_trackfd_neg1(self):
         size = 64
         with mmap.mmap(-1, size, trackfd=False) as m:
-            with self.assertRaises(OSError):
-                m.size()
             with self.assertRaises(ValueError):
-                m.resize(size // 2)
+                m.size()
+            if hasattr(m, 'resize'):
+                with self.assertRaises(ValueError):
+                    m.resize(size // 2)
             self.assertEqual(len(m), size)
             m[0] = ord('a')
             assert m[0] == ord('a')
 
-    @unittest.skipIf(os.name != 'nt', 'trackfd only fails on Windows')
-    def test_no_trackfd_parameter_on_windows(self):
-        # 'trackffd' is an invalid keyword argument for this function
-        size = 64
-        with self.assertRaises(TypeError):
-            mmap.mmap(-1, size, trackfd=True)
-        with self.assertRaises(TypeError):
-            mmap.mmap(-1, size, trackfd=False)
-
     def test_bad_file_desc(self):
         # Try opening a bad file descriptor...
         self.assertRaises(OSError, mmap.mmap, -2, 4096)
@@ -367,6 +357,8 @@ def test_find_end(self):
         self.assertEqual(m.find(b'one', 1, -1), 8)
         self.assertEqual(m.find(b'one', 1, -2), -1)
         self.assertEqual(m.find(bytearray(b'one')), 0)
+        self.assertEqual(m.find(b'', n + 1), -1)
+        self.assertEqual(m.rfind(b'', n + 1), -1)
 
         for i in range(-n-1, n+1):
             for j in range(-n-1, n+1):
@@ -510,6 +502,7 @@ def test_anonymous(self):
             b = x & 0xff
             m[x] = b
             self.assertEqual(m[x], b)
+        self.assertEqual(m.size(), PAGESIZE)
 
     @unittest.expectedFailureIfWindows("TODO: RUSTPYTHON")
     def test_read_all(self):
@@ -621,13 +614,9 @@ def test_offset (self):
             self.assertEqual(m[0:3], b'foo')
             f.close()
 
-            # Try resizing map
-            try:
+            if hasattr(m, 'resize'):
+                # Try resizing map
                 m.resize(512)
-            except SystemError:
-                pass
-            else:
-                # resize() is supported
                 self.assertEqual(len(m), 512)
                 # Check that we can no longer seek beyond the new size.
                 self.assertRaises(ValueError, m.seek, 513, 0)
@@ -825,14 +814,12 @@ def test_write_returning_the_number_of_bytes_written(self):
         self.assertEqual(mm.write(b"python"), 6)
 
     @unittest.expectedFailureIfWindows("TODO: RUSTPYTHON")
+    @unittest.skipUnless(hasattr(mmap.mmap, 'resize'), 'requires mmap.resize')
     def test_resize_past_pos(self):
         m = mmap.mmap(-1, 8192)
         self.addCleanup(m.close)
         m.read(5000)
-        try:
-            m.resize(4096)
-        except SystemError:
-            self.skipTest("resizing not supported")
+        m.resize(4096)
         self.assertEqual(m.read(14), b'')
         self.assertRaises(ValueError, m.read_byte)
         self.assertRaises(ValueError, m.write_byte, 42)
@@ -924,6 +911,7 @@ def __index__(self):
         self.assertEqual(m.madvise(mmap.MADV_NORMAL, 0, Number()), None)
         self.assertEqual(m.madvise(mmap.MADV_NORMAL, 0, size), None)
 
+    @unittest.skipUnless(hasattr(mmap.mmap, 'resize'), 'requires mmap.resize')
     def test_resize_up_anonymous_mapping(self):
         """If the mmap is backed by the pagefile ensure a resize up can happen
         and that the original data is still in place
@@ -934,23 +922,21 @@ def test_resize_up_anonymous_mapping(self):
 
         with mmap.mmap(-1, start_size) as m:
             m[:] = data
-            if sys.platform.startswith(('linux', 'android')):
-                # Can't expand a shared anonymous mapping on Linux.
-                # See https://bugzilla.kernel.org/show_bug.cgi?id=8691
+            if sys.platform.startswith(('linux', 'android', 'netbsd')):
+                # Can't expand a shared anonymous mapping on Linux
+                # (see https://bugzilla.kernel.org/show_bug.cgi?id=8691)
+                # or NetBSD.
                 with self.assertRaises(ValueError):
                     m.resize(new_size)
             else:
-                try:
-                    m.resize(new_size)
-                except SystemError:
-                    pass
-                else:
-                    self.assertEqual(len(m), new_size)
-                    self.assertEqual(m[:start_size], data)
-                    self.assertEqual(m[start_size:], b'\0' * (new_size - start_size))
+                m.resize(new_size)
+                self.assertEqual(len(m), new_size)
+                self.assertEqual(m[:start_size], data)
+                self.assertEqual(m[start_size:], b'\0' * (new_size - start_size))
 
     @unittest.expectedFailureIfWindows("TODO: RUSTPYTHON")
     @unittest.skipUnless(os.name == 'posix', 'requires Posix')
+    @unittest.skipUnless(hasattr(mmap.mmap, 'resize'), 'requires mmap.resize')
     def test_resize_up_private_anonymous_mapping(self):
         start_size = PAGESIZE
         new_size = 2 * start_size
@@ -958,16 +944,13 @@ def test_resize_up_private_anonymous_mapping(self):
 
         with mmap.mmap(-1, start_size, flags=mmap.MAP_PRIVATE) as m:
             m[:] = data
-            try:
-                m.resize(new_size)
-            except SystemError:
-                pass
-            else:
-                self.assertEqual(len(m), new_size)
-                self.assertEqual(m[:start_size], data)
-                self.assertEqual(m[start_size:], b'\0' * (new_size - start_size))
+            m.resize(new_size)
+            self.assertEqual(len(m), new_size)
+            self.assertEqual(m[:start_size], data)
+            self.assertEqual(m[start_size:], b'\0' * (new_size - start_size))
 
     @unittest.expectedFailureIfWindows("TODO: RUSTPYTHON")
+    @unittest.skipUnless(hasattr(mmap.mmap, 'resize'), 'requires mmap.resize')
     def test_resize_down_anonymous_mapping(self):
         """If the mmap is backed by the pagefile ensure a resize down up can happen
         and that a truncated form of the original data is still in place
@@ -978,17 +961,56 @@ def test_resize_down_anonymous_mapping(self):
 
         with mmap.mmap(-1, start_size) as m:
             m[:] = data
-            try:
-                m.resize(new_size)
-            except SystemError:
-                pass
-            else:
-                self.assertEqual(len(m), new_size)
-                self.assertEqual(m[:], data[:new_size])
-                if sys.platform.startswith(('linux', 'android')):
-                    # Can't expand to its original size.
-                    with self.assertRaises(ValueError):
-                        m.resize(start_size)
+            m.resize(new_size)
+            self.assertEqual(len(m), new_size)
+            self.assertEqual(m[:], data[:new_size])
+            if sys.platform.startswith(('linux', 'android')):
+                # Can't expand to its original size.
+                with self.assertRaises(ValueError):
+                    m.resize(start_size)
+
+    @unittest.skipUnless(hasattr(mmap.mmap, 'resize'), 'requires mmap.resize')
+    def test_setitem_resize_reentrancy(self):
+        """Resizing the mmap from inside __index__ while assigning to a
+        single item must not access memory past the new bounds (gh-157335).
+        """
+        size = 2 * PAGESIZE
+        new_size = PAGESIZE
+
+        class ResizeOnIndex:
+            def __init__(self, m):
+                self.m = m
+            def __index__(self):
+                self.m.resize(new_size)
+                return 0
+
+        with mmap.mmap(-1, size) as m:
+            with self.assertRaises(IndexError):
+                m[size - 1] = ResizeOnIndex(m)
+            self.assertEqual(len(m), new_size)
+
+    @unittest.skipUnless(hasattr(mmap.mmap, 'resize'), 'requires mmap.resize')
+    def test_setitem_slice_resize_reentrancy(self):
+        """Resizing the mmap from inside a value's buffer-protocol
+        callback while assigning to a slice must not access memory past
+        the new bounds (gh-157335).
+        """
+        size = 2 * PAGESIZE
+        new_size = PAGESIZE
+
+        class ResizeOnBuffer:
+            def __init__(self, m, data):
+                self.m = m
+                self.data = data
+            def __buffer__(self, flags):
+                self.m.resize(new_size)
+                return memoryview(self.data)
+
+        with mmap.mmap(-1, size) as m:
+            value = ResizeOnBuffer(m, bytes(size))
+            with self.assertRaises(IndexError):
+                m[0:size] = value
+            self.assertEqual(len(m), new_size)
 
     @unittest.expectedFailureIfWindows("TODO: RUSTPYTHON")
     @unittest.skipUnless(os.name == 'nt', 'requires Windows')
@@ -1197,6 +1219,74 @@ def test_access_violations(self):
         self.assertEqual(stdout.strip(), b'')
         self.assertEqual(stderr.strip(), b'')
 
+    def test_flush_parameters(self):
+        with open(TESTFN, 'wb+') as f:
+            f.write(b'x' * PAGESIZE * 3)
+            f.flush()
+
+            m = mmap.mmap(f.fileno(), PAGESIZE * 3)
+            self.addCleanup(m.close)
+
+            m.flush()
+            m.flush(PAGESIZE)
+            m.flush(PAGESIZE, PAGESIZE)
+
+            if hasattr(mmap, 'MS_SYNC'):
+                m.flush(0, PAGESIZE, flags=mmap.MS_SYNC)
+            if hasattr(mmap, 'MS_ASYNC'):
+                m.flush(flags=mmap.MS_ASYNC)
+            if hasattr(mmap, 'MS_INVALIDATE'):
+                m.flush(PAGESIZE * 2, flags=mmap.MS_INVALIDATE)
+            if hasattr(mmap, 'MS_ASYNC') and hasattr(mmap, 'MS_INVALIDATE'):
+                if sys.platform.startswith(('freebsd', 'dragonfly')):
+                    # FreeBSD and DragonFly don't support this combination
+                    with self.assertRaises(OSError) as cm:
+                        m.flush(0, PAGESIZE, flags=mmap.MS_ASYNC | mmap.MS_INVALIDATE)
+                    self.assertEqual(cm.exception.errno, errno.EINVAL)
+                else:
+                    m.flush(0, PAGESIZE, flags=mmap.MS_ASYNC | mmap.MS_INVALIDATE)
+
+    @unittest.skipUnless(sys.platform == 'linux', 'Linux only')
+    @support.requires_linux_version(5, 17, 0)
+    @unittest.skipIf(support.linked_to_musl(), "musl libc issue, gh-143632")
+    def test_set_name(self):
+        # Test setting name on anonymous mmap
+        m = mmap.mmap(-1, PAGESIZE)
+        self.addCleanup(m.close)
+        try:
+            result = m.set_name('test_mapping')
+        except OSError as exc:
+            if exc.errno == errno.EINVAL:
+                # gh-142419: On Fedora, prctl(PR_SET_VMA_ANON_NAME) fails with
+                # EINVAL because the kernel option CONFIG_ANON_VMA_NAME is
+                # disabled.
+                # See: https://bugzilla.redhat.com/show_bug.cgi?id=2302746
+                self.skipTest("prctl() failed with EINVAL")
+            else:
+                raise
+        self.assertIsNone(result)
+
+        # Test name length limit (80 chars including prefix "cpython:mmap:" and '\0')
+        # Prefix is 13 chars, so max name is 66 chars
+        long_name = 'x' * 66
+        result = m.set_name(long_name)
+        self.assertIsNone(result)
+
+        # Test name too long
+        too_long_name = 'x' * 67
+        with self.assertRaises(ValueError):
+            m.set_name(too_long_name)
+
+        # Test that file-backed mmap raises error
+        with open(TESTFN, 'wb+') as f:
+            f.write(b'x' * PAGESIZE)
+            f.flush()
+            m2 = mmap.mmap(f.fileno(), PAGESIZE)
+            self.addCleanup(m2.close)
+
+            with self.assertRaises(ValueError):
+                m2.set_name('should_fail')
+
 
 class LargeMmapTests(unittest.TestCase):
 
diff --git a/crates/host_env/src/mmap.rs b/crates/host_env/src/mmap.rs
index 976d78e2c38..4ce4c52a40d 100644
--- a/crates/host_env/src/mmap.rs
+++ b/crates/host_env/src/mmap.rs
@@ -7,8 +7,8 @@ use std::io;
 
 #[cfg(unix)]
 pub use libc::{
-    MADV_DONTNEED, MADV_NORMAL, MADV_RANDOM, MADV_SEQUENTIAL, MADV_WILLNEED, PROT_EXEC, PROT_READ,
-    PROT_WRITE,
+    MADV_DONTNEED, MADV_NORMAL, MADV_RANDOM, MADV_SEQUENTIAL, MADV_WILLNEED, MS_ASYNC,
+    MS_INVALIDATE, MS_SYNC, PROT_EXEC, PROT_READ, PROT_WRITE,
 };
 
 #[cfg(unix)]
@@ -202,10 +202,43 @@ impl MappedFile {
         }
     }
 
-    pub fn flush_range(&self, offset: usize, size: usize) -> io::Result<()> {
+    pub fn flush_range(&self, offset: usize, size: usize, flags: i32) -> io::Result<()> {
+        #[cfg(unix)]
+        {
+            if offset > self.as_slice().len() || size > self.as_slice().len() - offset {
+                return Err(io::Error::from_raw_os_error(libc::EINVAL));
+            }
+            let ptr = unsafe { self.as_ptr().add(offset) };
+            let flags = if flags == 0 { MS_SYNC } else { flags };
+            if unsafe { libc::msync(ptr.cast_mut().cast(), size, flags) } == -1 {
+                return Err(io::Error::last_os_error());
+            }
+            Ok(())
+        }
+        #[cfg(not(unix))]
+        {
+            let _ = flags;
+            match self {
+                Self::Read(_) => Ok(()),
+                Self::Write(mmap) => mmap.flush_range(offset, size),
+            }
+        }
+    }
+
+    /// # Safety
+    /// The backing file must cover the mapping offset plus `new_size`, and no
+    /// exported pointers may remain live while the mapping is moved or shrunk.
+    #[cfg(target_os = "linux")]
+    pub unsafe fn remap(&mut self, new_size: usize) -> io::Result<()> {
+        // memmap2 permits a zero-length mapping, whereas mmap.resize(0) must
+        // preserve mremap's EINVAL result.
+        if new_size == 0 {
+            return Err(io::Error::from_raw_os_error(libc::EINVAL));
+        }
+        let options = memmap2::RemapOptions::new().may_move(true);
         match self {
-            Self::Read(_) => Ok(()),
-            Self::Write(mmap) => mmap.flush_range(offset, size),
+            Self::Read(mmap) => unsafe { mmap.remap(new_size, options) },
+            Self::Write(mmap) => unsafe { mmap.remap(new_size, options) },
         }
     }
 
@@ -216,6 +249,23 @@ impl MappedFile {
     }
 }
 
+#[cfg(target_os = "linux")]
+pub fn set_mapping_name(address: usize, size: usize, name: &core::ffi::CStr) -> io::Result<()> {
+    if unsafe {
+        libc::prctl(
+            libc::PR_SET_VMA,
+            libc::PR_SET_VMA_ANON_NAME,
+            address,
+            size,
+            name.as_ptr(),
+        )
+    } == -1
+    {
+        return Err(io::Error::last_os_error());
+    }
+    Ok(())
+}
+
 #[cfg(windows)]
 unsafe impl Send for NamedMmap {}
 #[cfg(windows)]
@@ -293,16 +343,40 @@ pub fn file_len(fd: crt_fd::Borrowed<'_>) -> io::Result<i64> {
     Ok(fileutils::fstat(fd)?.st_size.into())
 }
 
+/// Inspect Python's raw descriptor without assuming that it is a valid Rust fd.
+/// CPython ignores failed fstat calls and only bounds regular-file mappings.
 #[cfg(unix)]
-pub fn prepare_file_mapping(fd: crt_fd::Borrowed<'_>) {
-    #[cfg(target_os = "macos")]
-    {
-        let _ = posix::full_fsync(fd.into());
+pub fn regular_file_len(fd: i32) -> Option<i64> {
+    // Use the same target selection as memmap2's mmap64/off64_t aliases.
+    #[cfg(not(any(
+        target_os = "android",
+        all(target_os = "linux", not(target_env = "musl"))
+    )))]
+    use libc::{fstat, stat as Stat};
+    #[cfg(any(
+        target_os = "android",
+        all(target_os = "linux", not(target_env = "musl"))
+    ))]
+    use libc::{fstat64 as fstat, stat64 as Stat};
+
+    let mut status = core::mem::MaybeUninit::<Stat>::uninit();
+    // SAFETY: fstat accepts an arbitrary integer and initializes status only
+    // on success. No borrowed/owned descriptor is constructed from that input.
+    if unsafe { fstat(fd, status.as_mut_ptr()) } != 0 {
+        return None;
     }
-    #[cfg(not(target_os = "macos"))]
-    {
-        let _ = fd;
+    let status = unsafe { status.assume_init() };
+    if status.st_mode & libc::S_IFMT != libc::S_IFREG {
+        return None;
     }
+    #[allow(clippy::useless_conversion, reason = "needed for 32-bit platforms")]
+    i64::try_from(status.st_size).ok()
+}
+
+#[cfg(target_os = "macos")]
+pub fn prepare_file_mapping(fd: i32) {
+    // CPython intentionally ignores F_FULLFSYNC errors, including invalid fds.
+    let _ = unsafe { libc::fcntl(fd, libc::F_FULLFSYNC) };
 }
 
 #[cfg(windows)]
@@ -409,25 +483,44 @@ pub fn map_anon(size: usize) -> io::Result<MappedFile> {
 }
 
 #[cfg(unix)]
-pub fn map_file(
-    fd: crt_fd::Borrowed<'_>,
-    offset: i64,
-    size: usize,
-    access: AccessMode,
-) -> io::Result<(crt_fd::Owned, MappedFile)> {
-    let new_fd: crt_fd::Owned = posix::dup_noninheritable(fd.into())?.into();
+pub fn duplicate_descriptor(fd: i32) -> io::Result<crt_fd::Owned> {
+    // Python supplies an arbitrary integer, so validate it through fcntl before
+    // constructing a Rust descriptor. Only the successful duplicate is owned.
+    let new_fd = unsafe { libc::fcntl(fd, libc::F_DUPFD_CLOEXEC, 0) };
+    if new_fd != -1 {
+        return Ok(unsafe { crt_fd::Owned::from_raw(new_fd) });
+    }
+    let err = io::Error::last_os_error();
+    if err.raw_os_error() != Some(libc::EINVAL) {
+        return Err(err);
+    }
+    // Older kernels may not support F_DUPFD_CLOEXEC.
+    let new_fd = unsafe { libc::dup(fd) };
+    if new_fd == -1 {
+        return Err(io::Error::last_os_error());
+    }
+    let new_fd = unsafe { crt_fd::Owned::from_raw(new_fd) };
+    posix::set_inheritable(new_fd.borrow().into(), false)?;
+    Ok(new_fd)
+}
+
+#[cfg(unix)]
+pub fn map_file(fd: i32, offset: i64, size: usize, access: AccessMode) -> io::Result<MappedFile> {
     let mut mmap_opt = MmapOptions::new();
     let mmap_opt = mmap_opt.offset(offset as u64).len(size);
 
+    // len is always explicit, so memmap2 never wraps this raw fd in File to
+    // query metadata. Its mmap syscall rejects invalid descriptors directly.
+    // The caller retains any owned tracking descriptor through this call.
     let mapped = match access {
         AccessMode::Default | AccessMode::Write => {
-            unsafe { mmap_opt.map_mut(&new_fd) }.map(MappedFile::Write)?
+            unsafe { mmap_opt.map_mut(fd) }.map(MappedFile::Write)?
         }
-        AccessMode::Read => unsafe { mmap_opt.map(&new_fd) }.map(MappedFile::Read)?,
-        AccessMode::Copy => unsafe { mmap_opt.map_copy(&new_fd) }.map(MappedFile::Write)?,
+        AccessMode::Read => unsafe { mmap_opt.map(fd) }.map(MappedFile::Read)?,
+        AccessMode::Copy => unsafe { mmap_opt.map_copy(fd) }.map(MappedFile::Write)?,
     };
 
-    Ok((new_fd, mapped))
+    Ok(mapped)
 }
 
 #[cfg(all(unix, not(target_os = "redox")))]
diff --git a/crates/stdlib/src/mmap.rs b/crates/stdlib/src/mmap.rs
index 790a7bc0fef..1064678a8f2 100644
--- a/crates/stdlib/src/mmap.rs
+++ b/crates/stdlib/src/mmap.rs
@@ -11,7 +11,7 @@ mod mmap {
     use crate::vm::{
         AsObject, FromArgs, Py, PyObject, PyObjectRef, PyPayload, PyRef, PyResult,
         TryFromBorrowedObject, VirtualMachine, atomic_func,
-        builtins::{PyBytes, PyBytesRef, PyInt, PyIntRef, PyType, PyTypeRef},
+        builtins::{PyBytes, PyBytesRef, PyInt, PyIntRef, PyType, PyTypeRef, PyUtf8StrRef},
         byte::{bytes_from_object, value_from_object},
         convert::ToPyException,
         function::{ArgBytesLike, ArgIndex},
@@ -72,7 +72,8 @@ mod mmap {
     #[pyattr]
     use host_mmap::{
         MADV_DONTNEED, MADV_NORMAL, MADV_RANDOM, MADV_SEQUENTIAL, MADV_WILLNEED, MAP_ANON,
-        MAP_ANONYMOUS, MAP_PRIVATE, MAP_SHARED, PROT_EXEC, PROT_READ, PROT_WRITE,
+        MAP_ANONYMOUS, MAP_PRIVATE, MAP_SHARED, MS_ASYNC, MS_INVALIDATE, MS_SYNC, PROT_EXEC,
+        PROT_READ, PROT_WRITE,
     };
 
     #[cfg(target_os = "macos")]
@@ -191,9 +192,6 @@ mod mmap {
         mmap: PyMutex<Option<MmapObj>>,
         #[cfg(unix)]
         fd: AtomicCell<i32>,
-        // only read by the linux/netbsd mremap expansion check
-        #[cfg(any(target_os = "linux", target_os = "netbsd"))]
-        flags: core::ffi::c_int,
         #[cfg(windows)]
         handle: AtomicCell<isize>, // host_mmap::Handle is isize on Windows
         offset: i64,
@@ -203,6 +201,10 @@ mod mmap {
         access: AccessMode,
         #[cfg(unix)]
         trackfd: bool,
+        #[cfg(target_os = "linux")]
+        anonymous: bool,
+        #[cfg(target_os = "linux")]
+        private: bool,
     }
 
     impl PyMmap {
@@ -296,6 +298,8 @@ mod mmap {
         offset: isize,
         #[pyarg(positional, optional)]
         size: Option<isize>,
+        #[pyarg(named, default)]
+        flags: core::ffi::c_int,
     }
 
     impl FlushOptions {
@@ -304,14 +308,15 @@ mod mmap {
                 return None;
             }
             let offset = self.offset as usize;
+            let remaining = len.checked_sub(offset)?;
 
             let size = match self.size {
+                None | Some(-1) => remaining,
                 Some(s) if s < 0 => return None,
                 Some(s) => s as usize,
-                None => len,
             };
 
-            if len.checked_sub(offset)? < size {
+            if remaining < size {
                 return None;
             }
 
@@ -408,10 +413,7 @@ mod mmap {
             }
 
             // TODO: memmap2 doesn't support mapping with prot and flags right now
-            #[cfg_attr(
-                not(any(target_os = "linux", target_os = "netbsd")),
-                allow(unused_variables)
-            )]
+            #[cfg_attr(not(target_os = "linux"), allow(unused_variables))]
             let (flags, _prot, access) = match access {
                 AccessMode::Read => (MAP_SHARED, PROT_READ, access),
                 AccessMode::Write => (MAP_SHARED, PROT_READ | PROT_WRITE, access),
@@ -428,24 +430,23 @@ mod mmap {
                 }
             };
 
-            let fd = unsafe { crt_fd::Borrowed::try_borrow_raw(fd) };
+            let anonymous = fd == -1 || flags & host_mmap::MAP_ANONYMOUS != 0;
 
-            // macOS: Issue #11277: fsync(2) is not enough on OS X - a special, OS X specific
-            // fcntl(2) is necessary to force DISKSYNC and get around mmap(2) bug
+            // Inspect the supplied descriptor before acquiring ownership, as
+            // CPython does. Invalid and non-regular fds do not impose file bounds.
             #[cfg(target_os = "macos")]
-            if let Ok(fd) = fd {
+            if fd != -1 {
                 host_mmap::prepare_file_mapping(fd);
             }
-
-            if let Ok(fd) = fd {
-                let file_len = host_mmap::file_len(fd).map_err(|err| err.to_pyexception(vm))?;
-
+            if fd != -1
+                && let Some(file_len) = host_mmap::regular_file_len(fd)
+            {
                 if map_size == 0 {
                     if file_len == 0 {
                         return Err(vm.new_value_error("cannot mmap an empty file"));
                     }
 
-                    if offset > file_len {
+                    if offset >= file_len {
                         return Err(vm.new_value_error("mmap offset is greater than file size"));
                     }
 
@@ -457,37 +458,40 @@ mod mmap {
                 }
             }
 
-            let (fd, mmap) = || -> std::io::Result<_> {
-                if let Ok(fd) = fd {
-                    let (new_fd, mmap) = host_mmap::map_file(
-                        fd,
-                        offset,
-                        map_size,
-                        match access {
-                            AccessMode::Default => host_mmap::AccessMode::Default,
-                            AccessMode::Read => host_mmap::AccessMode::Read,
-                            AccessMode::Write => host_mmap::AccessMode::Write,
-                            AccessMode::Copy => host_mmap::AccessMode::Copy,
-                        },
-                    )?;
-                    Ok((Some(new_fd), mmap))
-                } else {
-                    let mmap = host_mmap::map_anon(map_size)?;
-                    Ok((None, mmap))
-                }
-            }()
+            let retained_fd = if fd != -1 && trackfd {
+                Some(host_mmap::duplicate_descriptor(fd).map_err(|err| err.to_pyexception(vm))?)
+            } else {
+                None
+            };
+            let mmap = if anonymous {
+                host_mmap::map_anon(map_size)
+            } else {
+                // Keep an owned tracking fd alive through mmap when requested.
+                // Otherwise use the raw integer directly, without fabricating a
+                // BorrowedFd or creating a transient duplicate that can hit EMFILE.
+                let mapping_fd = retained_fd.as_ref().map_or(fd, |owned| owned.as_raw());
+                host_mmap::map_file(
+                    mapping_fd,
+                    offset,
+                    map_size,
+                    match access {
+                        AccessMode::Default => host_mmap::AccessMode::Default,
+                        AccessMode::Read => host_mmap::AccessMode::Read,
+                        AccessMode::Write => host_mmap::AccessMode::Write,
+                        AccessMode::Copy => host_mmap::AccessMode::Copy,
+                    },
+                )
+            }
             .map_err(|e| e.to_pyexception(vm))?;
 
             Ok(Self {
                 closed: AtomicCell::new(false),
                 mmap: PyMutex::new(Some(MmapObj::Mapped(mmap))),
-                fd: AtomicCell::new(if trackfd {
-                    fd.map_or(-1, |owned| owned.into_raw())
-                } else {
-                    -1
-                }),
-                #[cfg(any(target_os = "linux", target_os = "netbsd"))]
-                flags,
+                #[cfg(target_os = "linux")]
+                anonymous,
+                #[cfg(target_os = "linux")]
+                private: flags & MAP_PRIVATE != 0,
+                fd: AtomicCell::new(retained_fd.map_or(-1, |owned| owned.into_raw())),
                 offset,
                 size: AtomicCell::new(map_size),
                 pos: AtomicCell::new(0),
@@ -793,8 +797,7 @@ mod mmap {
             Ok(m)
         }
 
-        /// TODO: impl resize
-        #[allow(dead_code)]
+        #[cfg(any(target_os = "linux", windows, all(test, feature = "threading")))]
         fn check_resizeable(
             &self,
             vm: &VirtualMachine,
@@ -913,6 +916,8 @@ mod mmap {
 
         #[pymethod]
         fn flush(zelf: &Py<Self>, options: FlushOptions, vm: &VirtualMachine) -> PyResult<()> {
+            let mmap = zelf.check_valid(vm)?;
+            let flags = options.flags;
             let (offset, size) = options
                 .values(zelf.__len__())
                 .ok_or_else(|| vm.new_value_error("flush values out of range"))?;
@@ -921,9 +926,9 @@ mod mmap {
                 return Ok(());
             }
 
-            match zelf.check_valid(vm)?.deref().as_ref().unwrap() {
+            match mmap.deref().as_ref().unwrap() {
                 MmapObj::Mapped(mmap) => {
-                    mmap.flush_range(offset, size)
+                    mmap.flush_range(offset, size, flags)
                         .map_err(|e| e.to_pyexception(vm))?;
                 }
                 #[cfg(windows)]
@@ -937,15 +942,54 @@ mod mmap {
             Ok(())
         }
 
+        #[pymethod]
+        fn set_name(zelf: &Py<Self>, name: PyUtf8StrRef, vm: &VirtualMachine) -> PyResult<()> {
+            let name =
+                alloc::ffi::CString::new(name.as_str()).map_err(|err| err.to_pyexception(vm))?;
+            #[cfg(target_os = "linux")]
+            {
+                const PREFIX: &str = "cpython:mmap:";
+                if name.as_bytes().len() > 79 - PREFIX.len() {
+                    return Err(vm.new_value_error("name is too long"));
+                }
+                if !zelf.anonymous {
+                    return Err(
+                        vm.new_value_error("Cannot set annotation on non-anonymous mappings")
+                    );
+                }
+                // As in CPython's release build, kernel annotations are enabled
+                // only in development mode.
+                if vm.state.config.settings.dev_mode {
+                    let annotation =
+                        alloc::ffi::CString::new([PREFIX.as_bytes(), name.as_bytes()].concat())
+                            .expect("the name was checked for embedded NUL characters");
+                    let mmap = zelf.mmap.lock();
+                    let address = mmap
+                        .as_ref()
+                        .map_or(0, |mapping| mapping.as_slice().as_ptr() as usize);
+                    host_mmap::set_mapping_name(address, zelf.__len__(), &annotation)
+                        .map_err(|err| err.to_pyexception(vm))?;
+                }
+                Ok(())
+            }
+            #[cfg(not(target_os = "linux"))]
+            {
+                let _ = (zelf, name);
+                Err(vm.new_not_implemented_error(
+                    "Annotation of mmap is not supported on this platform",
+                ))
+            }
+        }
+
         #[cfg(all(unix, not(target_os = "redox")))]
         #[pymethod]
         fn madvise(zelf: &Py<Self>, options: AdviseOptions, vm: &VirtualMachine) -> PyResult<()> {
+            let guard = zelf.check_valid(vm)?;
             let (option, start, length) = options.values(zelf.__len__(), vm)?;
             if !host_mmap::validate_advice(option) {
                 return Err(vm.new_value_error("Not a valid Advice value"));
             }
 
-            let guard = zelf.check_valid(vm)?;
             let mmap = guard.deref().as_ref().unwrap();
             match mmap {
                 MmapObj::Mapped(m) => m.madvise_range(start, length, option),
@@ -987,14 +1031,13 @@ mod mmap {
                 Some((dest, src, cnt))
             }
 
-            let size = zelf.__len__();
-            let (dest, src, cnt) = args(dest.as_ref(), src.as_ref(), count.as_ref(), size, vm)
-                .ok_or_else(|| vm.new_value_error("source, destination, or count out of range"))?;
-
-            let dest_end = dest + cnt;
-            let src_end = src + cnt;
-
             zelf.try_writable(vm, |mmap| {
+                let (dest, src, cnt) =
+                    args(dest.as_ref(), src.as_ref(), count.as_ref(), mmap.len(), vm).ok_or_else(
+                        || vm.new_value_error("source, destination, or count out of range"),
+                    )?;
+                let dest_end = dest + cnt;
+                let src_end = src + cnt;
                 let src_buf = mmap[src..src_end].to_vec();
                 (&mut mmap[dest..dest_end])
                     .write(&src_buf)
@@ -1025,6 +1068,9 @@ mod mmap {
                 .filter(|&n| n >= 0 && (n as usize) <= remaining)
                 .map_or(remaining, |n| n as usize);
 
+            if num_bytes == 0 {
+                return Ok(PyBytes::from(vec![]).into_ref(&vm.ctx));
+            }
             let end_pos = pos + num_bytes;
             let bytes = mmap.deref().as_ref().unwrap().as_slice()[pos..end_pos].to_vec();
 
@@ -1037,12 +1083,13 @@ mod mmap {
 
         #[pymethod]
         fn read_byte(zelf: &Py<Self>, vm: &VirtualMachine) -> PyResult<PyIntRef> {
+            let mmap = zelf.check_valid(vm)?;
             let pos = zelf.pos();
             if pos >= zelf.__len__() {
                 return Err(vm.new_value_error("read byte out of range"));
             }
 
-            let b = zelf.check_valid(vm)?.deref().as_ref().unwrap().as_slice()[pos];
+            let b = mmap.deref().as_ref().unwrap().as_slice()[pos];
 
             zelf.advance_pos(1);
 
@@ -1077,29 +1124,38 @@ mod mmap {
             Ok(result)
         }
 
-        #[cfg(unix)]
+        #[cfg(target_os = "linux")]
         #[pymethod]
         fn resize(zelf: &Py<Self>, newsize: PyIntRef, vm: &VirtualMachine) -> PyResult<()> {
-            drop(zelf.check_resizeable(vm)?);
-
-            let new_size: isize = newsize.try_to_primitive(vm).map_err(|_| {
+            let newsize: isize = newsize.try_to_primitive(vm).map_err(|_| {
                 vm.new_overflow_error("Python int too large to convert to C ssize_t")
             })?;
-
-            // Linux mremap() refuses to grow a shared anonymous mapping, and NetBSD
-            // mremap() returns a mapping whose grown region is not backed.
-            #[cfg(any(target_os = "linux", target_os = "netbsd"))]
-            if zelf.fd.load() == -1
-                && zelf.flags & host_mmap::MAP_PRIVATE == 0
-                && new_size > zelf.size.load() as isize
-            {
+            // Reject exports before taking the data lock, and retain the guard
+            // through truncation and remapping so a new export cannot race us.
+            let mut mmap = zelf.check_resizeable(vm)?;
+            let file_size = i128::from(zelf.offset) + newsize as i128;
+            if newsize < 0 || file_size > isize::MAX as i128 {
+                return Err(vm.new_value_error("new size out of range"));
+            }
+            let newsize = newsize as usize;
+            if zelf.anonymous && !zelf.private && newsize > zelf.__len__() {
                 return Err(vm.new_value_error("mmap: can't expand a shared anonymous mapping"));
             }
-
-            // TODO: implement using mremap on Linux
-            #[cfg(not(any(target_os = "linux", target_os = "netbsd")))]
-            let _ = new_size;
-            Err(vm.new_system_error("mmap: resizing not available--no mremap()"))
+            let fd = zelf.fd.load();
+            if fd != -1 {
+                let fd = unsafe { crt_fd::Borrowed::try_borrow_raw(fd) }
+                    .map_err(|err| err.to_pyexception(vm))?;
+                let file_size = file_size
+                    .try_into()
+                    .map_err(|_| vm.new_value_error("new size out of range"))?;
+                crt_fd::ftruncate(fd, file_size).map_err(|err| err.to_pyexception(vm))?;
+            }
+            let MmapObj::Mapped(mapping) = mmap.as_mut().unwrap();
+            // The mapping is locked, exported buffers are prohibited, and its
+            // backing file has already been resized to cover the new mapping.
+            unsafe { mapping.remap(newsize) }.map_err(|err| err.to_pyexception(vm))?;
+            zelf.size.store(newsize);
+            Ok(())
         }
 
         #[cfg(windows)]
@@ -1237,15 +1293,25 @@ mod mmap {
 
         #[cfg(unix)]
         #[pymethod]
-        fn size(zelf: &Py<Self>, vm: &VirtualMachine) -> std::io::Result<PyIntRef> {
-            let fd = unsafe { crt_fd::Borrowed::try_borrow_raw(zelf.fd.load())? };
-            let file_len = host_mmap::file_len(fd)?;
+        fn size(zelf: &Py<Self>, vm: &VirtualMachine) -> PyResult<PyIntRef> {
+            let _mmap = zelf.check_valid(vm)?;
+            if !zelf.trackfd {
+                return Err(vm.new_value_error("can't get size with trackfd=False"));
+            }
+            let fd = zelf.fd.load();
+            if fd == -1 {
+                return Ok(PyInt::from(zelf.__len__()).into_ref(&vm.ctx));
+            }
+            let fd = unsafe { crt_fd::Borrowed::try_borrow_raw(fd) }
+                .map_err(|err| err.to_pyexception(vm))?;
+            let file_len = host_mmap::file_len(fd).map_err(|err| err.to_pyexception(vm))?;
             Ok(PyInt::from(file_len).into_ref(&vm.ctx))
         }
 
         #[cfg(windows)]
         #[pymethod]
         fn size(zelf: &Py<Self>, vm: &VirtualMachine) -> PyResult<PyIntRef> {
+            let _mmap = zelf.check_valid(vm)?;
             let handle = zelf.handle.load();
             if host_mmap::is_invalid_handle_value(handle) {
                 // Anonymous mapping, return the mmap size
@@ -1271,7 +1337,6 @@ mod mmap {
         fn write(zelf: &Py<Self>, bytes: ArgBytesLike, vm: &VirtualMachine) -> PyResult<PyIntRef> {
             let self_ = &**zelf;
             let pos = self_.pos();
-            let size = self_.__len__();
 
             // Writing locks the map, and reading a source that views this same
             // map locks it too, so such a source is copied out first.
@@ -1285,11 +1350,10 @@ mod mmap {
                 &borrowed
             };
 
-            if pos > size || size - pos < data.len() {
-                return Err(vm.new_value_error("data out of range"));
-            }
-
             let len = self_.try_writable(vm, |mmap| {
+                if pos > mmap.len() || mmap.len() - pos < data.len() {
+                    return Err(vm.new_value_error("data out of range"));
+                }
                 (&mut mmap[pos..(pos + data.len())])
                     .write(data)
                     .map_err(|err| err.to_pyexception(vm))?;
@@ -1306,15 +1370,13 @@ mod mmap {
             let b = value_from_object(vm, &byte)?;
 
             let pos = zelf.pos();
-            let size = zelf.__len__();
-
-            if pos >= size {
-                return Err(vm.new_value_error("write byte out of range"));
-            }
-
             zelf.try_writable(vm, |mmap| {
+                if pos >= mmap.len() {
+                    return Err(vm.new_value_error("write byte out of range"));
+                }
                 mmap[pos] = b;
-            })?;
+                Ok(())
+            })??;
 
             zelf.advance_pos(1);
 
@@ -1397,11 +1459,12 @@ mod mmap {
         }
 
         fn getitem_by_index(&self, i: isize, vm: &VirtualMachine) -> PyResult<PyObjectRef> {
+            let mmap = self.check_valid(vm)?;
             let i = i
                 .wrapped_at(self.__len__())
                 .ok_or_else(|| vm.new_index_error("mmap index out of range"))?;
 
-            let b = self.check_valid(vm)?.deref().as_ref().unwrap().as_slice()[i];
+            let b = mmap.deref().as_ref().unwrap().as_slice()[i];
 
             Ok(PyInt::from(b).into_ref(&vm.ctx).into())
         }
@@ -1411,9 +1474,8 @@ mod mmap {
             slice: &SaturatedSlice,
             vm: &VirtualMachine,
         ) -> PyResult<PyObjectRef> {
-            let (range, step, slice_len) = slice.adjust_indices(self.__len__());
-
             let mmap = self.check_valid(vm)?;
+            let (range, step, slice_len) = slice.adjust_indices(self.__len__());
             let slice_data = mmap.deref().as_ref().unwrap().as_slice();
 
             if slice_len == 0 {