core.fsyncmethod: add writeout-only mode

This commit introduces the `core.fsyncMethod` configuration
knob, which can currently be set to `fsync` or `writeout-only`.

The new writeout-only mode attempts to tell the operating system to
flush its in-memory page cache to the storage hardware without issuing a
CACHE_FLUSH command to the storage controller.

Writeout-only fsync is significantly faster than a vanilla fsync on
common hardware, since data is written to a disk-side cache rather than
all the way to a durable medium. Later changes in this patch series will
take advantage of this primitive to implement batching of hardware
flushes.

When git_fsync is called with FSYNC_WRITEOUT_ONLY, it may fail and the
caller is expected to do an ordinary fsync as needed.

On Apple platforms, the fsync system call does not issue a CACHE_FLUSH
directive to the storage controller. This change updates fsync to do
fcntl(F_FULLFSYNC) to make fsync actually durable. We maintain parity
with existing behavior on Apple platforms by setting the default value
of the new core.fsyncMethod option.

Signed-off-by: Neeraj Singh <neerajsi@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
pull/1230/head
Neeraj Singh 7 months ago committed by Junio C Hamano
parent 19d3f228c8
commit abf38abec2
  1. 9
      Documentation/config/core.txt
  2. 6
      Makefile
  3. 7
      cache.h
  4. 3
      compat/mingw.h
  5. 28
      compat/win32/flush.c
  6. 12
      config.c
  7. 3
      config.mak.uname
  8. 8
      configure.ac
  9. 16
      contrib/buildsystems/CMakeLists.txt
  10. 1
      environment.c
  11. 24
      git-compat-util.h
  12. 64
      wrapper.c
  13. 11
      write-or-die.c

@ -547,6 +547,15 @@ core.whitespace::
is relevant for `indent-with-non-tab` and when Git fixes `tab-in-indent`
errors. The default tab width is 8. Allowed values are 1 to 63.
core.fsyncMethod::
A value indicating the strategy Git will use to harden repository data
using fsync and related primitives.
+
* `fsync` uses the fsync() system call or platform equivalents.
* `writeout-only` issues pagecache writeback requests, but depending on the
filesystem and storage hardware, data added to the repository may not be
durable in the event of a system crash. This is the default mode on macOS.
core.fsyncObjectFiles::
This boolean will enable 'fsync()' when writing object files.
+

@ -411,6 +411,8 @@ all::
#
# Define HAVE_CLOCK_MONOTONIC if your platform has CLOCK_MONOTONIC.
#
# Define HAVE_SYNC_FILE_RANGE if your platform has sync_file_range.
#
# Define NEEDS_LIBRT if your platform requires linking with librt (glibc version
# before 2.17) for clock_gettime and CLOCK_MONOTONIC.
#
@ -1897,6 +1899,10 @@ ifdef HAVE_CLOCK_MONOTONIC
BASIC_CFLAGS += -DHAVE_CLOCK_MONOTONIC
endif
ifdef HAVE_SYNC_FILE_RANGE
BASIC_CFLAGS += -DHAVE_SYNC_FILE_RANGE
endif
ifdef NEEDS_LIBRT
EXTLIBS += -lrt
endif

@ -995,6 +995,13 @@ extern char *git_replace_ref_base;
extern int fsync_object_files;
extern int use_fsync;
enum fsync_method {
FSYNC_METHOD_FSYNC,
FSYNC_METHOD_WRITEOUT_ONLY
};
extern enum fsync_method fsync_method;
extern int core_preload_index;
extern int precomposed_unicode;
extern int protect_hfs;

@ -329,6 +329,9 @@ int mingw_getpagesize(void);
#define getpagesize mingw_getpagesize
#endif
int win32_fsync_no_flush(int fd);
#define fsync_no_flush win32_fsync_no_flush
struct rlimit {
unsigned int rlim_cur;
};

@ -0,0 +1,28 @@
#include "git-compat-util.h"
#include <winternl.h>
#include "lazyload.h"
int win32_fsync_no_flush(int fd)
{
IO_STATUS_BLOCK io_status;
#define FLUSH_FLAGS_FILE_DATA_ONLY 1
DECLARE_PROC_ADDR(ntdll.dll, NTSTATUS, NTAPI, NtFlushBuffersFileEx,
HANDLE FileHandle, ULONG Flags, PVOID Parameters, ULONG ParameterSize,
PIO_STATUS_BLOCK IoStatusBlock);
if (!INIT_PROC_ADDR(NtFlushBuffersFileEx)) {
errno = ENOSYS;
return -1;
}
memset(&io_status, 0, sizeof(io_status));
if (NtFlushBuffersFileEx((HANDLE)_get_osfhandle(fd), FLUSH_FLAGS_FILE_DATA_ONLY,
NULL, 0, &io_status)) {
errno = EINVAL;
return -1;
}
return 0;
}

@ -1600,6 +1600,18 @@ static int git_default_core_config(const char *var, const char *value, void *cb)
return 0;
}
if (!strcmp(var, "core.fsyncmethod")) {
if (!value)
return config_error_nonbool(var);
if (!strcmp(value, "fsync"))
fsync_method = FSYNC_METHOD_FSYNC;
else if (!strcmp(value, "writeout-only"))
fsync_method = FSYNC_METHOD_WRITEOUT_ONLY;
else
warning(_("ignoring unknown core.fsyncMethod value '%s'"), value);
}
if (!strcmp(var, "core.fsyncobjectfiles")) {
fsync_object_files = git_config_bool(var, value);
return 0;

@ -57,6 +57,7 @@ ifeq ($(uname_S),Linux)
HAVE_CLOCK_MONOTONIC = YesPlease
# -lrt is needed for clock_gettime on glibc <= 2.16
NEEDS_LIBRT = YesPlease
HAVE_SYNC_FILE_RANGE = YesPlease
HAVE_GETDELIM = YesPlease
FREAD_READS_DIRECTORIES = UnfortunatelyYes
BASIC_CFLAGS += -DHAVE_SYSINFO
@ -463,6 +464,7 @@ endif
CFLAGS =
BASIC_CFLAGS = -nologo -I. -Icompat/vcbuild/include -DWIN32 -D_CONSOLE -DHAVE_STRING_H -D_CRT_SECURE_NO_WARNINGS -D_CRT_NONSTDC_NO_DEPRECATE
COMPAT_OBJS = compat/msvc.o compat/winansi.o \
compat/win32/flush.o \
compat/win32/path-utils.o \
compat/win32/pthread.o compat/win32/syslog.o \
compat/win32/trace2_win32_process_info.o \
@ -640,6 +642,7 @@ ifeq ($(uname_S),MINGW)
COMPAT_CFLAGS += -DSTRIP_EXTENSION=\".exe\"
COMPAT_OBJS += compat/mingw.o compat/winansi.o \
compat/win32/trace2_win32_process_info.o \
compat/win32/flush.o \
compat/win32/path-utils.o \
compat/win32/pthread.o compat/win32/syslog.o \
compat/win32/dirent.o

@ -1082,6 +1082,14 @@ AC_COMPILE_IFELSE([CLOCK_MONOTONIC_SRC],
[AC_MSG_RESULT([no])
HAVE_CLOCK_MONOTONIC=])
GIT_CONF_SUBST([HAVE_CLOCK_MONOTONIC])
#
# Define HAVE_SYNC_FILE_RANGE=YesPlease if sync_file_range is available.
GIT_CHECK_FUNC(sync_file_range,
[HAVE_SYNC_FILE_RANGE=YesPlease],
[HAVE_SYNC_FILE_RANGE])
GIT_CONF_SUBST([HAVE_SYNC_FILE_RANGE])
#
# Define NO_SETITIMER if you don't have setitimer.
GIT_CHECK_FUNC(setitimer,

@ -261,10 +261,18 @@ if(CMAKE_SYSTEM_NAME STREQUAL "Windows")
NOGDI OBJECT_CREATION_MODE=1 __USE_MINGW_ANSI_STDIO=0
USE_NED_ALLOCATOR OVERRIDE_STRDUP MMAP_PREVENTS_DELETE USE_WIN32_MMAP
UNICODE _UNICODE HAVE_WPGMPTR ENSURE_MSYSTEM_IS_SET HAVE_RTLGENRANDOM)
list(APPEND compat_SOURCES compat/mingw.c compat/winansi.c compat/win32/path-utils.c
compat/win32/pthread.c compat/win32mmap.c compat/win32/syslog.c
compat/win32/trace2_win32_process_info.c compat/win32/dirent.c
compat/nedmalloc/nedmalloc.c compat/strdup.c)
list(APPEND compat_SOURCES
compat/mingw.c
compat/winansi.c
compat/win32/flush.c
compat/win32/path-utils.c
compat/win32/pthread.c
compat/win32mmap.c
compat/win32/syslog.c
compat/win32/trace2_win32_process_info.c
compat/win32/dirent.c
compat/nedmalloc/nedmalloc.c
compat/strdup.c)
set(NO_UNIX_SOCKETS 1)
elseif(CMAKE_SYSTEM_NAME STREQUAL "Linux")

@ -44,6 +44,7 @@ int zlib_compression_level = Z_BEST_SPEED;
int pack_compression_level = Z_DEFAULT_COMPRESSION;
int fsync_object_files;
int use_fsync = -1;
enum fsync_method fsync_method = FSYNC_METHOD_DEFAULT;
size_t packed_git_window_size = DEFAULT_PACKED_GIT_WINDOW_SIZE;
size_t packed_git_limit = DEFAULT_PACKED_GIT_LIMIT;
size_t delta_base_cache_limit = 96 * 1024 * 1024;

@ -1271,6 +1271,30 @@ __attribute__((format (printf, 1, 2))) NORETURN
void BUG(const char *fmt, ...);
#endif
#ifdef __APPLE__
#define FSYNC_METHOD_DEFAULT FSYNC_METHOD_WRITEOUT_ONLY
#else
#define FSYNC_METHOD_DEFAULT FSYNC_METHOD_FSYNC
#endif
enum fsync_action {
FSYNC_WRITEOUT_ONLY,
FSYNC_HARDWARE_FLUSH
};
/*
* Issues an fsync against the specified file according to the specified mode.
*
* FSYNC_WRITEOUT_ONLY attempts to use interfaces available on some operating
* systems to flush the OS cache without issuing a flush command to the storage
* controller. If those interfaces are unavailable, the function fails with
* ENOSYS.
*
* FSYNC_HARDWARE_FLUSH does an OS writeout and hardware flush to ensure that
* changes are durable. It is not expected to fail.
*/
int git_fsync(int fd, enum fsync_action action);
/*
* Preserves errno, prints a message, but gives no warning for ENOENT.
* Returns 0 on success, which includes trying to unlink an object that does

@ -546,6 +546,70 @@ int xmkstemp_mode(char *filename_template, int mode)
return fd;
}
/*
* Some platforms return EINTR from fsync. Since fsync is invoked in some
* cases by a wrapper that dies on failure, do not expose EINTR to callers.
*/
static int fsync_loop(int fd)
{
int err;
do {
err = fsync(fd);
} while (err < 0 && errno == EINTR);
return err;
}
int git_fsync(int fd, enum fsync_action action)
{
switch (action) {
case FSYNC_WRITEOUT_ONLY:
#ifdef __APPLE__
/*
* On macOS, fsync just causes filesystem cache writeback but
* does not flush hardware caches.
*/
return fsync_loop(fd);
#endif
#ifdef HAVE_SYNC_FILE_RANGE
/*
* On linux 2.6.17 and above, sync_file_range is the way to
* issue a writeback without a hardware flush. An offset of
* 0 and size of 0 indicates writeout of the entire file and the
* wait flags ensure that all dirty data is written to the disk
* (potentially in a disk-side cache) before we continue.
*/
return sync_file_range(fd, 0, 0, SYNC_FILE_RANGE_WAIT_BEFORE |
SYNC_FILE_RANGE_WRITE |
SYNC_FILE_RANGE_WAIT_AFTER);
#endif
#ifdef fsync_no_flush
return fsync_no_flush(fd);
#endif
errno = ENOSYS;
return -1;
case FSYNC_HARDWARE_FLUSH:
/*
* On macOS, a special fcntl is required to really flush the
* caches within the storage controller. As of this writing,
* this is a very expensive operation on Apple SSDs.
*/
#ifdef __APPLE__
return fcntl(fd, F_FULLFSYNC);
#else
return fsync_loop(fd);
#endif
default:
BUG("unexpected git_fsync(%d) call", action);
}
}
static int warn_if_unremovable(const char *op, const char *file, int rc)
{
int err;

@ -62,10 +62,13 @@ void fsync_or_die(int fd, const char *msg)
use_fsync = git_env_bool("GIT_TEST_FSYNC", 1);
if (!use_fsync)
return;
while (fsync(fd) < 0) {
if (errno != EINTR)
die_errno("fsync error on '%s'", msg);
}
if (fsync_method == FSYNC_METHOD_WRITEOUT_ONLY &&
git_fsync(fd, FSYNC_WRITEOUT_ONLY) >= 0)
return;
if (git_fsync(fd, FSYNC_HARDWARE_FLUSH) < 0)
die_errno("fsync error on '%s'", msg);
}
void write_or_die(int fd, const void *buf, size_t count)

Loading…
Cancel
Save