cudaFree不释放内存 [英] cudaFree is not freeing memory

问题描述

下面的代码计算两个向量a和b的点积。正确的结果是8192.当我第一次运行它的结果是正确的。然后当我第二次运行它的结果是以前的结果+ 8192等：

The code below calculates the dot product of two vectors a and b. The correct result is 8192. When I run it for the first time the result is correct. Then when I run it for the second time the result is the previous result + 8192 and so on:

1st iteration: result = 8192
2nd iteration: result = 8192 + 8192
3rd iteration: result = 8192 + 8192 
and so on.

通过在屏幕上打印并检查设备变量dev_c不被释放。更多的写入它会导致像一个和，结果beeing以前的值加上一个新的写入它。我想这可能是与atomicAdd（）操作的东西，但仍然cudaFree（dev_c）应该擦除它毕竟。

I checked by printing it on screen and the device variable dev_c is not freed. What's more writing to it causes something like a sum, the result beeing the previous value plus the new one being written to it. I guess that could be something with the atomicAdd() operation, but nonetheless cudaFree(dev_c) should erase it after all.

#define N 8192
#define THREADS_PER_BLOCK 512
#define NUMBER_OF_BLOCKS (N/THREADS_PER_BLOCK)
#include <stdio.h>


__global__ void dot( int *a, int *b, int *c ) {

    __shared__ int temp[THREADS_PER_BLOCK];

    int index = threadIdx.x + blockIdx.x * blockDim.x;

    temp[threadIdx.x] = a[index] * b[index];

    __syncthreads();

    if( 0 == threadIdx.x ) {

        int sum = 0;
        for( int i= 0; i< THREADS_PER_BLOCK; i++ ){
        sum += temp[i];
        }
        atomicAdd(c,sum);
    }
}

    int main( void ) {

        int *a, *b, *c;
        int *dev_a, *dev_b, *dev_c; 
        int size = N * sizeof( int); 

        cudaMalloc( (void**)&dev_a, size );
        cudaMalloc( (void**)&dev_b, size );
        cudaMalloc( (void**)&dev_c, sizeof(int));

        a = (int*)malloc(size);
        b = (int*)malloc(size);
        c = (int*)malloc(sizeof(int));

        for(int i = 0 ; i < N ; i++){
            a[i] = 1;
            b[i] = 1;
        }

        cudaMemcpy( dev_a, a, size, cudaMemcpyHostToDevice);
        cudaMemcpy( dev_b, b, size, cudaMemcpyHostToDevice);

        dot<<< N/THREADS_PER_BLOCK,THREADS_PER_BLOCK>>>( dev_a, dev_b, dev_c);

        cudaMemcpy( c, dev_c, sizeof(int) , cudaMemcpyDeviceToHost);

        printf("Dot product = %d\n", *c);

        cudaFree(dev_a);
        cudaFree(dev_b);
        cudaFree(dev_c);    

        free(a); 
        free(b); 
        free(c);

        return 0;

    }

推荐答案

cudaFree不删除任何东西，它只是将内存返回到池重新分配。 cudaMalloc不保证已分配的内存的值。您需要初始化您的程序使用的内存（全局和共享），以获得一致的结果。 malloc和免费也是如此，顺便说一句。

cudaFree doesn't erase anything, it simply returns memory to a pool to be re-allocated. cudaMalloc doesn't guarantee the value of memory that has been allocated. You need to initialize memory (both global and shared) that your program uses, in order to have consistent results. The same is true for malloc and free, by the way.

这篇关于cudaFree不释放内存的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！