windows 如何使文件系统缓存失效?

eni9jsuy  于 2022-11-18  发布在  Windows
关注(0)|答案(5)|浏览(160)

我希望测量/优化应用程序的“冷 Boot ”启动性能,如果不进行实际的重新启动,很难做到这一点,这显然不是一个理想的解决方案。
有没有一种方法可以使整个系统的文件缓存无效,这样Map的页面访问实际上会导致磁盘访问,这样我就可以测量程序启动所需的时间?

信息:

我非常需要FSCTL_DISMOUNT_VOLUME的功能,但对于系统卷。

vs91vp4v

vs91vp4v1#

至少在Windows 7上,尝试在没有 * FILE_SHARE_WRITE共享权限**的情况下打开卷句柄 * 似乎会导致文件系统缓存无效***, 即使创建失败 *。
因此,我编写了一个程序,它只需要调用CreateFile即可。
从以下网址下载Base64版本的程序 *:

<!-- Click "Run Snippet", then Right-Click -> Save As... -->
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来源

// Usage: ClearCache C: D:
#include <tchar.h>
#include <stdio.h>
#include <windows.h>

int _tmain(int argc, LPTSTR argv[]) {
    LPCTSTR DOS_PREFIX = _T("\\\\.\\");
    for (int i = 1; i < argc; i++) {
        LPTSTR arg = argv[i];
        LPTSTR path = (LPTSTR)calloc(
            _tcslen(arg) + _tcslen(DOS_PREFIX) + 1, sizeof(*arg));
        __try {
            if (_istalpha(arg[0]) && arg[1] == _T(':') &&
               (arg[2] == _T('\0') ||
                arg[2] == _T('\\') && arg[3] == _T('\0')))
            { _tcscat(path, DOS_PREFIX); }
            _tcscat(path, arg);
            HANDLE hFile = CreateFile(path,
                FILE_READ_DATA, FILE_SHARE_READ, NULL, OPEN_EXISTING, 0, NULL);
            if (hFile != INVALID_HANDLE_VALUE) { CloseHandle(hFile); }
            else {
                DWORD le = GetLastError();
                if (le != ERROR_SHARING_VIOLATION && le != ERROR_ACCESS_DENIED)
                {
                    _ftprintf(stderr, _T("Error %d clearing %s\n"), le, argv[i]);
                    return le;
                }
            }
        } __finally { free(path); }
    }
    return 0;
}
  • 只是为了好玩,看看你是否能通过反汇编它来弄清楚可执行文件的作用。它不是你典型的可执行文件。:)
uqdfh47h

uqdfh47h2#

我已经编写了一个简单的命令行实用程序来实现这一点:FlushFileCache
它依赖于未记录的NtSetSystemInformation函数,并且还可以刷新各种其他内存池。

rsaldnfx

rsaldnfx3#

该解决方案非常有效:* 清除文件缓存以重复性能测试 *
更具体地说,我是这样做的:

// Open with FILE_FLAG_NO_BUFFERING
auto hFile = CreateFile(path.c_str(),
                        GENERIC_READ,
                        FILE_SHARE_READ,
                        nullptr,
                        OPEN_EXISTING,
                        FILE_FLAG_NO_BUFFERING,
                        nullptr);

/// Check
if (hFile == INVALID_HANDLE_VALUE){
    //_tprintf(TEXT("Terminal failure: unable to open file \"%s\" for read.\n"), argv[1]);
    cout << "error" << endl;
    return;
}

// Close
CloseHandle(hFile);

// Now open file with regular C++ API, and caching disabled
ifstream file(path, ios::binary | ios::ate);
whitzsjs

whitzsjs4#

大卫说的。创建一个大文件,无论你需要多少GB,每次你想重置你的文件缓存时,都要复制一份文件。然后确保你删除了旧文件。
因此,创建BIGFILE1.DAT,将其复制到BIGFILE2.DAT,然后删除BIGFILE1.DAT(这会将其从磁盘和该高速缓存中删除)。
附录:
另一种方法是将Map的文件复制到新文件中,删除旧文件,并将新文件重命名为旧文件。该高速缓存由文件支持。如果文件“消失”,缓存也会消失。
如果您可以识别这些文件,并且它们不被系统/其他正在运行的程序共享,那么编写脚本应该很简单,并且理想情况下,运行速度比复制6 GB的文件要快。

drkbr07n

drkbr07n5#

您可以使用VM并在VM引导后立即拍摄快照。从快照恢复比重新引导快。

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