[PATCH] macOS: queue for munmap operations
From: Koji Nakamaru via GitGitGadget <hidden>
Date: 2025-10-20 22:35:05
Subsystem:
kernel build + files below scripts/ (unless maintained elsewhere), the rest · Maintainers:
Nathan Chancellor, Nicolas Schier, Linus Torvalds
From: Koji Nakamaru <redacted>
Executing many mmap/munmap calls alternately can cause a huge load on
macOS. In order to reduce it, we should temporarily store munmap
operations in a queue and process them all at once when the queue is
filled. When the program terminates, we can discard any remaining munmap
operations as corresponding mmaped regions are automatically reclaimed.
Add a queue for munmap operations to perform them all at once.
Here are some example timings. On the Linux kernel repository that
requires about 1700 mmap/munmap calls:
time git ls-tree -r -l --full-tree 211ddde > /dev/null
Before:
real 0m2.083s
user 0m0.201s
sys 0m1.873s
After:
real 0m0.243s
user 0m0.179s
sys 0m0.052s
On a private repository that requires about 943000 mmap/munmap calls:
time git ls-tree -r -l --full-tree xxxxxxx > /dev/null
Before:
real 27m15.138s
user 0m5.084s
sys 27m9.636s
After:
real 0m24.209s
user 0m3.055s
sys 0m21.123s
Signed-off-by: Koji Nakamaru <redacted>
---
macOS: queue for munmap operations
Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-1993%2FKojiNakamaru%2Ffeature%2Fosx-queued-munmap-v1
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-1993/KojiNakamaru/feature/osx-queued-munmap-v1
Pull-Request: https://github.com/gitgitgadget/git/pull/1993
Makefile | 1 +
compat/osxmmap.c | 49 +++++++++++++++++++++++++++++
compat/posix.h | 7 +++++
contrib/buildsystems/CMakeLists.txt | 4 +++
meson.build | 2 ++
5 files changed, 63 insertions(+)
create mode 100644 compat/osxmmap.c
diff --git a/Makefile b/Makefile
index f79c905bdc..058bc83753 100644
--- a/Makefile
+++ b/Makefile@@ -1654,6 +1654,7 @@ ifeq ($(uname_S),Darwin) COMPAT_CFLAGS += -DAPPLE_COMMON_CRYPTO endif PTHREAD_LIBS = + COMPAT_OBJS += compat/osxmmap.o endif ifdef NO_LIBGEN_H
diff --git a/compat/osxmmap.c b/compat/osxmmap.c
new file mode 100644
index 0000000000..5f9cf633ca
--- /dev/null
+++ b/compat/osxmmap.c@@ -0,0 +1,49 @@ +#include <pthread.h> +#include "../git-compat-util.h" +/* We need original mmap/munmap here. */ +#undef mmap +#undef munmap + +/* + * OSX doesn't have any specific setting like Linux's vm.max_map_count, + * so COUNT_MAX can be any large number. We here set it to the default + * value of Linux's vm.max_map_count. + */ +#define COUNT_MAX (65530) + +struct munmap_queue { + void *start; + size_t length; +}; + +void *git_mmap(void *start, size_t length, int prot, int flags, int fd, off_t offset) +{ + /* + * We can simply discard munmap operations in the queue by + * restricting mmap arguments. + */ + if (start != NULL || flags != MAP_PRIVATE || prot != PROT_READ) + die("invalid usage of mmap"); + return mmap(start, length, prot, flags, fd, offset); +} + +int git_munmap(void *start, size_t length) +{ + static pthread_mutex_t mutex; + static struct munmap_queue *queue; + static int count; + int i; + + pthread_mutex_lock(&mutex); + if (!queue) + queue = xmalloc(COUNT_MAX * sizeof(struct munmap_queue)); + queue[count].start = start; + queue[count].length = length; + if (++count == COUNT_MAX) { + for (i = 0; i < COUNT_MAX; i++) + munmap(queue[i].start, queue[i].length); + count = 0; + } + pthread_mutex_unlock(&mutex); + return 0; +}
diff --git a/compat/posix.h b/compat/posix.h
index 067a00f33b..3fa1218289 100644
--- a/compat/posix.h
+++ b/compat/posix.h@@ -278,6 +278,13 @@ int git_munmap(void *start, size_t length); #include <sys/mman.h> +#if defined(__APPLE__) +#define mmap git_mmap +#define munmap git_munmap +void *git_mmap(void *start, size_t length, int prot, int flags, int fd, off_t offset); +int git_munmap(void *start, size_t length); +#endif + #endif /* NO_MMAP || USE_WIN32_MMAP */ #ifndef MAP_FAILED
diff --git a/contrib/buildsystems/CMakeLists.txt b/contrib/buildsystems/CMakeLists.txt
index edb0fc04ad..5c08f2fe5c 100644
--- a/contrib/buildsystems/CMakeLists.txt
+++ b/contrib/buildsystems/CMakeLists.txt@@ -271,6 +271,10 @@ if(CMAKE_SYSTEM_NAME STREQUAL "Windows") compat/strdup.c) set(NO_UNIX_SOCKETS 1) +elseif(CMAKE_SYSTEM_NAME STREQUAL "Darwin") + list(APPEND compat_SOURCES + compat/osxmmap.c) + elseif(CMAKE_SYSTEM_NAME STREQUAL "Linux") add_compile_definitions(PROCFS_EXECUTABLE_PATH="/proc/self/exe" HAVE_DEV_TTY ) list(APPEND compat_SOURCES unix-socket.c unix-stream-server.c compat/linux/procinfo.c)
diff --git a/meson.build b/meson.build
index cee9424475..b9b6e731b1 100644
--- a/meson.build
+++ b/meson.build@@ -1275,6 +1275,8 @@ elif host_machine.system() == 'windows' else libgit_sources += 'compat/mingw.c' endif +elif host_machine.system() == 'darwin' + libgit_sources += 'compat/osxmmap.c' endif if host_machine.system() == 'linux'
base-commit: 4253630c6f07a4bdcc9aa62a50e26a4d466219d1 -- gitgitgadget