记录 Linux 进程的 RAM 内存高水位标记

记录 Linux 进程的 RAM 内存高水位标记

我想在 Linux 进程(内核 3.2.0-36)完成时记录该进程的 RAM 内存最高水位标记。我正在 Perl 脚本中调用该进程。类似于:

my $cmd = "logmemory -o mem.log mycmd options 1>cmd.out 2>cmd.err";
unless(system("$cmd") == 0) { die $!; }

有任何想法吗?

答案1

看一下/proc/[pid]/status,特别是这个参数。

  • 虚拟机HWM:峰值驻留集大小(“高水位标记”)。

或者,您可以使用/usr/bin/time -v命令。以下是其输出的示例:

Command exited with non-zero status 1
    Command being timed: "xz -9ek access_log.3 access_log.xz"
    User time (seconds): 6.96
    System time (seconds): 0.34
    Percent of CPU this job got: 99%
    Elapsed (wall clock) time (h:mm:ss or m:ss): 0:07.34
    Average shared text size (kbytes): 0
    Average unshared data size (kbytes): 0
    Average stack size (kbytes): 0
    Average total size (kbytes): 0
  **Maximum resident set size (kbytes): 383456**
    Average resident set size (kbytes): 0
    Major (requiring I/O) page faults: 0
    Minor (reclaiming a frame) page faults: 24000
    Voluntary context switches: 3
    Involuntary context switches: 225
    Swaps: 0
    File system inputs: 0
    File system outputs: 0
    Socket messages sent: 0
    Socket messages received: 0
    Signals delivered: 0
    Page size (bytes): 4096
    Exit status: 1

答案2

内核已经为您收集了进程的 RAM 高水位信息(来自man proc):

/proc/[pid]/status
Provides much of the information in /proc/[pid]/stat and /proc/[pid]/statm in a format that's easier for humans to parse.
(...)
* VmHWM: Peak resident set size ("high water mark").
(...)

棘手的部分是,这个值应该在进程终止前立即读取

我尝试了不同的方法(在答案的最后有更多相关内容),对我有用的方法是用 C 语言实现:

  • logmemory调用fork()来创建子进程。

  • 子进程调用,以便每次子进程执行系统调用时,ptrace()父进程(即)都会得到通知。logmemory

  • 子进程使用execvp()来运行mycmd

  • logmemory耐心等待通知。如果是,它会检查是否已mycmd调用exit_group。如果是,它会读取/proc/<pid>/status,将值复制到子进程mem.log并从子进程分离。否则,logmemory允许mycmd继续并等待下一个通知。

缺点是会ptrace()减慢被监控程序的速度,下面我展示一些比较。

此版本logmemory不仅有日志VmHWM,还有:

  • VmPeak(峰值虚拟内存大小,包括所有代码、数据和共享库以及已换出的页面和已映射但未使用的页面)

  • 时间戳

  • 命令名称和参数

这是代码,肯定可以改进 - 我不精通 C 语言。但它按预期工作(在 32 位 Ubuntu 12.04 和 64 位 SuSE Linux Enterprise Server 10 SP4 上测试):

// logmemory.c
#include <stdio.h>
#include <sys/ptrace.h>
#include <unistd.h>
#include <syscall.h>
#include <sys/reg.h>
#include <stdlib.h>
#include <string.h>
#include <time.h>

#define STRINGLENGTH 2048

int main(int argc, char **argv)
{   
    pid_t child_pid;
    long syscall;
    int status, index;
    FILE *statusfile, *logfile;
    char opt, statusfile_path[STRINGLENGTH], line[STRINGLENGTH], command[STRINGLENGTH], logfile_path[STRINGLENGTH] = "";
    time_t now;
    extern char *optarg;
    extern int optind;

    // Error checking
    if (argc == 1) {
        printf("Error: program to execute is missing. Exiting...\n");
        return 0;
    }
    // Get options
    while ((opt = getopt (argc, argv, "+o:")) != -1)
        switch (opt) {
            case 'o':
                strncpy(logfile_path, optarg, 2048);
                break;
            case ':':
                fprintf (stderr, "Aborting: argument for option -o is missing\n");
                return 1;
            case '?':
                fprintf (stderr, "Aborting: only valid option is -o\n");
                return 1;
    }
    // More error checking
    if (!strcmp(logfile_path, "")) {
        fprintf(stderr, "Error: log filename can't be empty\n");
        return 1;
    }
    child_pid = fork();
    // The child process executes this:
    if (child_pid == 0) {
        // Trace child process:
        ptrace(PTRACE_TRACEME, 0, NULL, NULL);
        // Execute command using $PATH
        execvp(argv[optind], (char * const *)(argv+optind));

    // The parent process executes this:
    } else {
        // Loop until child process terminates
        do {
            // Set ptrace to stop when syscall is executed
            ptrace(PTRACE_SYSCALL, child_pid, NULL, NULL);
            wait(&status);
            // Get syscall number
            syscall = ptrace(PTRACE_PEEKUSER, child_pid,
#ifdef __i386__
                          4 * ORIG_EAX,
#else
                          8 * ORIG_RAX,
#endif
                          NULL);
        } while (syscall != SYS_exit_group);

        // Construct path to status file and check whether status and log file can be opened
        snprintf(statusfile_path, STRINGLENGTH, "/proc/%d/status", child_pid);
        if ( !(logfile = fopen(logfile_path, "a+")) || !(statusfile = fopen(statusfile_path, "r")) ) {
            ptrace(PTRACE_DETACH, child_pid, NULL, NULL);
            return 1;
        }

        // Copy timestamp and command to logfile
        now = time(NULL);
        fprintf(logfile, "Date: %sCmd: ", asctime(localtime(&now)));
        for (index = optind; index < argc; index++)
           fprintf(logfile, " %s", argv[index]);
        fprintf(logfile, "\n");

        // Read status file line by line and copy lines containing VmPeak and VmHWM to logfile
        while (fgets(line, STRINGLENGTH, statusfile)) {
            if (strstr(line,"VmPeak") || strstr(line,"VmHWM"))
                fprintf(logfile, "%s", line);
        }
        fprintf(logfile, "\n");

        // Close files
        fclose(statusfile);
        fclose(logfile);

        // Detach from child process
        ptrace(PTRACE_DETACH, child_pid, NULL, NULL);
    }
    return 0;
}

将其保存logmemory.c并编译如下:

$ gcc logmemory.c -o logmemory

像这样运行:

$ ./logmemory 
Error: program to execute is missing. Exiting...
$ ./logmemory -o mem.log ls -l
(...)
$ ./logmemory -o mem.log free
             total       used       free     shared    buffers     cached
Mem:       1025144     760660     264484          0       6644     143980
-/+ buffers/cache:     610036     415108
Swap:      1046524     544228     502296
$ ./logmemory -o mem.log find /tmp -name \*txt
(...)
$ cat mem.log
Date: Mon Feb 11 21:17:55 2013
Cmd:  ls -l
VmPeak:     5004 kB
VmHWM:      1284 kB

Date: Mon Feb 11 21:18:01 2013
Cmd:  free
VmPeak:     2288 kB
VmHWM:       448 kB

Date: Mon Feb 11 21:18:26 2013
Cmd:  find /tmp -name *txt
VmPeak:     4700 kB
VmHWM:       908 kB

我编写了这个 C 程序来测试logmemory的准确性:

// bigmalloc.c
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#define ITERATIONS 200
int main(int argc, char **argv)
{
    int i=0;
    for (i=0; i<ITERATIONS; i++) {
        void *m = malloc(1024*1024);
        memset(m,0,1024*1024);
    }
    return 0;
}

照常编译并在里面运行logmemory

$ gcc bigmalloc.c -o bigmalloc
$ ./logmemory -o mem.log ./bigmalloc
$ tail mem.log

Date: Mon Feb 11 21:26:01 2013
Cmd:  ./bigmalloc
VmPeak:   207604 kB
VmHWM:    205932 kB

正确报告使用了200 MB。

附注:(time至少在 Ubuntu 12.04 上)令人惊讶地输出一个与内核报告的值有很大不同的值:

$ /usr/bin/time --format %M ./bigmalloc
823872

其中M(来自man time):

M   Maximum resident set size of the process during its lifetime, in Kilobytes.

如上所述,这是有代价的,因为它logmemory会减慢被监控程序的执行速度,例如:

$ time ./logmemory -o mem.log ./bigmalloc
real    0m0.288s
user    0m0.000s
sys     0m0.004s
$ time ./bigmalloc
real    0m0.104s
user    0m0.008s
sys     0m0.092s

$ time find /var -name \*log
(...)
real    0m0.036s
user    0m0.000s
sys     0m0.032s
$ time ./logmemory -o mem.log find /var -name \*log
(...)
real    0m0.124s
user    0m0.000s
sys     0m0.052s

我尝试过(但没有成功)的其他方法包括:

  • /proc/<pid>/status创建一个后台进程以便在运行时读取的 shell 脚本mycmd

  • 一个可以派生并执行mycmd但暂停直到子进程变为僵尸进程的程序,因此可以避免ptrace它产生的开销。我认为这是一个好主意,但不幸的是,对于僵尸进程来说VmHWM,它VmPeak已经不再可用了。/proc/<pid>/status

答案3

尽管这个话题已经很老了,我还是想分享另一个源自 cgroups Linux 内核功能的项目。

https://github.com/gsauthof/cgmemtime

cgmemtime 测量一个进程及其后代进程的高水位 RSS+CACHE 内存使用情况。

为了做到这一点,它将进程放入其自己的 cgroup 中。

例如,进程 A 分配 10 MiB,并派生出一个子进程 B,后者分配 20 MiB,后者派生出一个子进程 C,后者分配 30 MiB。这三个进程共享一个时间窗口,在此期间,它们的分配将产生相应的 RSS(驻留集大小)内存使用量。

现在的问题是:运行 A 实际使用了多少内存?

答案:60 MiB

cgmemtime 就是用来回答此类问题的工具。

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