在MPI中一定数量的iovec之后，进程vm readv失败

Question

我正在使用process_vm_readv在MPI中将数据从一个进程获取到另一个进程。我发现在为process_vm_readv提供一定数量的iovec（在本例中为1024）之后，该程序将开始垃圾。我不确定发生了什么，内核是否耗尽了内存？或我的代码有问题。还是process_vm_readv对iovec有上限？我为iovec自生成了一个矢量模式（每16个字节中有8个字节）。程序将一直运行，直到两个线程上的此模式都填充了1GB。分别为sbuf和rbuf分配了1GB的内存。该程序位于24GB以上的计算机上。

void do_test( int slen, int rlen, int scount, int rcount, void *sbuf, void *rbuf ){
int rank, err;
double timers[REP];
MPI_Win win;
pid_t pid;

MPI_Comm_rank( MPI_COMM_WORLD, &rank );
if( rank == 0 ){
    MPI_Win_create( NULL, 0, 1, MPI_INFO_NULL, MPI_COMM_WORLD, &win );

    int send_iovcnt;
    struct iovec *send_iov;

    struct iovec *iov = malloc( sizeof(struct iovec) * scount );
    for( int p = 0; p < scount; p++ ){
        iov[p].iov_base = (char*)rbuf + p * 16;
        iov[p].iov_len = 8;
    }

    MPI_Recv( &pid, sizeof(pid_t), MPI_BYTE, 1, 0, MPI_COMM_WORLD, MPI_STATUS_IGNORE );
    MPI_Recv( &send_iovcnt, 1, MPI_INT, 1, 1, MPI_COMM_WORLD, MPI_STATUS_IGNORE );

    send_iov = malloc( sizeof(struct iovec) * send_iovcnt );

    MPI_Recv( send_iov, sizeof(struct iovec) * send_iovcnt, MPI_BYTE, 1, 2, MPI_COMM_WORLD, MPI_STATUS_IGNORE );
    for( int i = 0; i < REP; i++ ){
        cache_flush();
        timers[i] = MPI_Wtime();
        MPI_Win_fence( 0, win );
        process_vm_readv( pid, iov, send_iovcnt, send_iov, send_iovcnt, 0 );
        MPI_Win_fence( 0, win );
        cache_flush();
        timers[i] = MPI_Wtime() - timers[i];
    }
    free(send_iov);
    free(iov);

    print_result( 8 * scount, REP, timers );
} else if( rank == 1 ){
    MPI_Win_create( sbuf, slen, 1, MPI_INFO_NULL, MPI_COMM_WORLD, &win );

    struct iovec *iov = malloc( sizeof(struct iovec) * rcount );

    for( int p = 0; p < rcount; p++ ){
        iov[p].iov_base = (char*)sbuf + p * 16;
        iov[p].iov_base = 8;
    }

    pid = getpid();
    MPI_Send( &pid, sizeof(pid_t), MPI_BYTE, 0, 0, MPI_COMM_WORLD );
    MPI_Send( &rcount, 1, MPI_INT, 0, 1, MPI_COMM_WORLD );
    MPI_Send( iov, rcount * sizeof(struct iovec), MPI_BYTE, 0, 2, MPI_COMM_WORLD );
    for( int i = 0; i < REP; i++ ){
        cache_flush();
        MPI_Win_fence( 0, win );
        MPI_Win_fence( 0, win );
    }
    free(iov);

}

Answer 1

在man page of process_vm_readv(2)中找到以下文本：

process_vm_readv(2)和liovcnt参数中指定的值必须小于或等于riovcnt（在IOV_MAX中定义，或可通过调用<limits.h>进行访问。）

在我的Linux系统上，sysconf(_SC_IOV_MAX)的值（最终在IOV_MAX中定义）为1024。