diff --git a/libc/SECCOMP_WHITELIST_COMMON.TXT b/libc/SECCOMP_WHITELIST_COMMON.TXT
index a2114dd..07f84a8 100644
--- a/libc/SECCOMP_WHITELIST_COMMON.TXT
+++ b/libc/SECCOMP_WHITELIST_COMMON.TXT
@@ -68,28 +68,24 @@
 # Useful new syscalls which we don't yet use in bionic.
 #
 
-# Since Linux 3.14, not in glibc.
-int sched_getattr(pid_t pid, struct sched_attr* attr, unsigned int flags) all
-int sched_setattr(pid_t pid, struct sched_attr* attr, unsigned int size, unsigned int flags) all
-# Since Linux 3.15, glibc 2.27.
-int memfd_create(const char* name, unsigned int flags) all
-# Since Linux 3.19, not in glibc.
-int execveat(int dirfd, const char* pathname, char* const* argv, char* const* envp, int flags)  all
-# Since Linux 4.3, not in glibc. Probed for and conditionally used by ART.
-int membarrier(int cmd, int flags) all
-# Since Linux 4.5, glibc 2.27.
-ssize_t copy_file_range(int fd_in, loff_t* off_in, int fd_out, loff_t* off_out, size_t len, unsigned int flags) all
-# Since Linux 4.4, glibc 2.27.
-int mlock2(const void* addr, size_t len, int flags) all
-# Since Linux 4.6, glibc 2.26.
-ssize_t preadv2(int fd, const struct iovec* iov, int iovcnt, off_t offset, int flags) all
-ssize_t pwritev2(int fd, const struct iovec* iov, int iovcnt, off_t offset, int flags) all
 # Since Linux 2.5, not in glibc.
 int io_setup(unsigned nr, aio_context_t *ctxp) all
 int io_destroy(aio_context_t ctx) all
 int io_submit(aio_context_t ctx, long nr,  struct iocb **iocbpp) all
 int io_getevents(aio_context_t ctx, long min_nr, long max_nr, struct io_event *events, struct timespec *timeout) all
 int io_cancel(aio_context_t ctx, struct iocb *, struct io_event *result) all
+# Since Linux 3.14, not in glibc.
+int sched_getattr(pid_t pid, struct sched_attr* attr, unsigned int flags) all
+int sched_setattr(pid_t pid, struct sched_attr* attr, unsigned int size, unsigned int flags) all
+# Since Linux 3.19, not in glibc (and not really needed to implement fexecve).
+int execveat(int dirfd, const char* pathname, char* const* argv, char* const* envp, int flags)  all
+# Since Linux 4.3, not in glibc. Probed for and conditionally used by ART.
+int membarrier(int cmd, int flags) all
+# Since Linux 4.5, glibc 2.27.
+ssize_t copy_file_range(int fd_in, loff_t* off_in, int fd_out, loff_t* off_out, size_t len, unsigned int flags) all
+# Since Linux 4.6, glibc 2.26.
+ssize_t preadv2(int fd, const struct iovec* iov, int iovcnt, off_t offset, int flags) all
+ssize_t pwritev2(int fd, const struct iovec* iov, int iovcnt, off_t offset, int flags) all
 # Since Linux 4.11, glibc 2.30.
 int statx(int, const char*, int, unsigned int, statx*) all
 # Since Linux 5.1, not in glibc.
diff --git a/libc/SYSCALLS.TXT b/libc/SYSCALLS.TXT
index 62d698f..21ebdbd 100644
--- a/libc/SYSCALLS.TXT
+++ b/libc/SYSCALLS.TXT
@@ -107,12 +107,14 @@
 
 int         __close:close(int)  all
 pid_t       __getpid:getpid()  all
+int memfd_create(const char*, unsigned) all
 int         munmap(void*, size_t)  all
 void*       __mremap:mremap(void*, size_t, size_t, int, void*)  all
 int         msync(const void*, size_t, int)    all
 int         mprotect(const void*, size_t, int)  all
 int         madvise(void*, size_t, int)  all
-int         mlock(const void* addr, size_t len)    all
+int mlock(const void* addr, size_t len)    all
+int mlock2(const void* addr, size_t len, int flags)    all
 int         munlock(const void* addr, size_t len)   all
 int         mlockall(int flags)   all
 int         munlockall()   all
diff --git a/libc/include/sys/mman.h b/libc/include/sys/mman.h
index 89d6d07..3b83229 100644
--- a/libc/include/sys/mman.h
+++ b/libc/include/sys/mman.h
@@ -26,34 +26,27 @@
  * SUCH DAMAGE.
  */
 
-#ifndef _SYS_MMAN_H_
-#define _SYS_MMAN_H_
+#pragma once
 
 #include <sys/cdefs.h>
 #include <sys/types.h>
+#include <linux/memfd.h>
 #include <linux/mman.h>
 
 __BEGIN_DECLS
 
-#ifndef MAP_ANON
-#define MAP_ANON  MAP_ANONYMOUS
-#endif
+/** Alternative spelling of the `MAP_ANONYMOUS` flag for mmap(). */
+#define MAP_ANON MAP_ANONYMOUS
 
+/** Return value for mmap(). */
 #define MAP_FAILED __BIONIC_CAST(reinterpret_cast, void*, -1)
 
-#define MREMAP_MAYMOVE  1
-#define MREMAP_FIXED    2
-
-/*
- * See https://android.googlesource.com/platform/bionic/+/master/docs/32-bit-abi.md
+/**
+ * [mmap(2)](http://man7.org/linux/man-pages/man2/mmap.2.html)
+ * creates a memory mapping for the given range.
  *
- * mmap64 wasn't really around until L, but we added an inline for it since it
- * allows a lot more code to compile with _FILE_OFFSET_BITS=64.
- *
- * GCC removes the static inline unless it is explicitly used. We can get around
- * this with __attribute__((used)), but that needlessly adds a definition of
- * mmap64 to every translation unit that includes this header. Instead, just
- * preserve the old behavior for GCC and emit a useful diagnostic.
+ * Returns the address of the mapping on success,
+ * and returns `MAP_FAILED` and sets `errno` on failure.
  */
 #if defined(__USE_FILE_OFFSET64)
 void* mmap(void* __addr, size_t __size, int __prot, int __flags, int __fd, off_t __offset) __RENAME(mmap64);
@@ -62,25 +55,126 @@
 #endif
 
 #if __ANDROID_API__ >= __ANDROID_API_L__
+/**
+ * mmap64() is a variant of mmap() that takes a 64-bit offset even on LP32.
+ *
+ * See https://android.googlesource.com/platform/bionic/+/master/docs/32-bit-abi.md
+ *
+ * mmap64 wasn't really around until L, but we added an inline for it since it
+ * allows a lot more code to compile with _FILE_OFFSET_BITS=64.
+ */
 void* mmap64(void* __addr, size_t __size, int __prot, int __flags, int __fd, off64_t __offset) __INTRODUCED_IN(21);
 #endif
 
+/**
+ * [munmap(2)](http://man7.org/linux/man-pages/man2/munmap.2.html)
+ * deletes a memory mapping for the given range.
+ *
+ * Returns 0 on success, and returns -1 and sets `errno` on failure.
+ */
 int munmap(void* __addr, size_t __size);
+
+/**
+ * [msync(2)](http://man7.org/linux/man-pages/man2/msync.2.html)
+ * flushes changes to a memory-mapped file to disk.
+ *
+ * Returns 0 on success, and returns -1 and sets `errno` on failure.
+ */
 int msync(void* __addr, size_t __size, int __flags);
+
+/**
+ * [mprotect(2)](http://man7.org/linux/man-pages/man2/mprotect.2.html)
+ * sets the protection on a memory region.
+ *
+ * Returns 0 on success, and returns -1 and sets `errno` on failure.
+ */
 int mprotect(void* __addr, size_t __size, int __prot);
+
+/** Flag for mremap(). */
+#define MREMAP_MAYMOVE  1
+
+/** Flag for mremap(). */
+#define MREMAP_FIXED    2
+
+/**
+ * [mremap(2)](http://man7.org/linux/man-pages/man2/mremap.2.html)
+ * expands or shrinks an existing memory mapping.
+ *
+ * Returns the address of the mapping on success,
+ * and returns `MAP_FAILED` and sets `errno` on failure.
+ */
 void* mremap(void* __old_addr, size_t __old_size, size_t __new_size, int __flags, ...);
 
+/**
+ * [mlockall(2)](http://man7.org/linux/man-pages/man2/mlockall.2.html)
+ * locks pages (preventing swapping).
+ *
+ * Returns 0 on success, and returns -1 and sets `errno` on failure.
+ */
 int mlockall(int __flags) __INTRODUCED_IN(17);
+
+/**
+ * [munlockall(2)](http://man7.org/linux/man-pages/man2/munlockall.2.html)
+ * unlocks pages (allowing swapping).
+ *
+ * Returns 0 on success, and returns -1 and sets `errno` on failure.
+ */
 int munlockall(void) __INTRODUCED_IN(17);
 
+/**
+ * [mlock(2)](http://man7.org/linux/man-pages/man2/mlock.2.html)
+ * locks pages (preventing swapping).
+ *
+ * Returns 0 on success, and returns -1 and sets `errno` on failure.
+ */
 int mlock(const void* __addr, size_t __size);
+
+/**
+ * [mlock2(2)](http://man7.org/linux/man-pages/man2/mlock.2.html)
+ * locks pages (preventing swapping), with optional flags.
+ *
+ * Returns 0 on success, and returns -1 and sets `errno` on failure.
+ */
+int mlock2(const void* __addr, size_t __size, int __flags) __INTRODUCED_IN(30);
+
+/**
+ * [munlock(2)](http://man7.org/linux/man-pages/man2/munlock.2.html)
+ * unlocks pages (allowing swapping).
+ *
+ * Returns 0 on success, and returns -1 and sets `errno` on failure.
+ */
 int munlock(const void* __addr, size_t __size);
 
+/**
+ * [mincore(2)](http://man7.org/linux/man-pages/man2/mincore.2.html)
+ * tests whether pages are resident in memory.
+ *
+ * Returns 0 on success, and returns -1 and sets `errno` on failure.
+ */
 int mincore(void* __addr, size_t __size, unsigned char* __vector);
 
+/**
+ * [madvise(2)](http://man7.org/linux/man-pages/man2/madvise.2.html)
+ * gives the kernel advice about future usage patterns.
+ *
+ * Returns 0 on success, and returns -1 and sets `errno` on failure.
+ */
 int madvise(void* __addr, size_t __size, int __advice);
 
+#if defined(__USE_GNU)
+
+/**
+ * [memfd_create(2)](http://man7.org/linux/man-pages/man2/memfd_create.2.html)
+ * creates an anonymous file.
+ *
+ * Returns an fd on success, and returns -1 and sets `errno` on failure.
+ */
+int memfd_create(const char* __name, unsigned __flags) __INTRODUCED_IN(30);
+
+#endif
+
 #if __ANDROID_API__ >= __ANDROID_API_M__
+
 /*
  * Some third-party code uses the existence of POSIX_MADV_NORMAL to detect the
  * availability of posix_madvise. This is not correct, since having up-to-date
@@ -89,16 +183,30 @@
  *
  * https://github.com/android-ndk/ndk/issues/395
  */
+
+/** Flag for posix_madvise(). */
 #define POSIX_MADV_NORMAL     MADV_NORMAL
+/** Flag for posix_madvise(). */
 #define POSIX_MADV_RANDOM     MADV_RANDOM
+/** Flag for posix_madvise(). */
 #define POSIX_MADV_SEQUENTIAL MADV_SEQUENTIAL
+/** Flag for posix_madvise(). */
 #define POSIX_MADV_WILLNEED   MADV_WILLNEED
+/** Flag for posix_madvise(). */
 #define POSIX_MADV_DONTNEED   MADV_DONTNEED
+
 #endif
+
+/**
+ * [posix_madvise(3)](http://man7.org/linux/man-pages/man3/posix_madvise.3.html)
+ * gives the kernel advice about future usage patterns.
+ *
+ * Returns 0 on success, and returns a positive error number on failure.
+ *
+ * See also madvise() which has been available much longer.
+ */
 int posix_madvise(void* __addr, size_t __size, int __advice) __INTRODUCED_IN(23);
 
 __END_DECLS
 
 #include <android/legacy_sys_mman_inlines.h>
-
-#endif
diff --git a/libc/libc.map.txt b/libc/libc.map.txt
index c3b9e2c..9b39bb8 100644
--- a/libc/libc.map.txt
+++ b/libc/libc.map.txt
@@ -1493,6 +1493,8 @@
     cnd_signal;
     cnd_timedwait;
     cnd_wait;
+    memfd_create;
+    mlock2;
     mtx_destroy;
     mtx_init;
     mtx_lock;