CUBLAS memory allocation error - c++

Question

I tried to allocate 17338896 elements of floating point numbers as follows (which is roughly 70 mb):
state = cublasAlloc(theSim->Ndim*theSim->Ndim,
sizeof(*(theSim->K0)),
(void**)&K0cuda);
if(state != CUBLAS_STATUS_SUCCESS) {
printf("Error allocation video memory.\n");
return -1;
}
However, I'm receiving error message of CUBLAS_STATUS_ALLOC_FAILED for the variable state. Would this have anything to do with the amount of video card memory available on the machine (128 mb on mine) or would this be a limit of the amount of memory that I can allocate using cublasAlloc() function (i.e. not relevant to the amount of memory available on the machine)? I tried using cudaMalloc() function and I am running into the same problem. Thanks in advance for looking into this.
--------------Addition of Error Reproduction-------------------------------------
#include <cuda.h>
#include <stdio.h>
int main (int argc, char *argv[]) {
// CUDA setup
cublasStatus state;
if(cublasInit() == CUBLAS_STATUS_NOT_INITIALIZED) {
printf("CUBLAS init error.\n");
return -1;
}
// Instantiate video memory pointers
float *K0cuda;
// Allocate video memory needed
state = cublasAlloc(20000000,
sizeof(float),
(void**)&K0cuda);
if(state != CUBLAS_STATUS_SUCCESS) {
printf("Error allocation video memory.\n");
return -1;
}
// Copy K0 from CPU memory to GPU memory
// Note: before so, decide whether to integrate as a part of InsertionSim or
// CUDA content as a separate class
//state = cublasSetMatrix(theSim->Ndim, theSim->Ndim, sizeof(*theSim->K0),
// theSim->K0, theSim->Ndim, K0cuda, theSim->Ndim);
//if(state != CUBLAS_STATUS_SUCCESS) {
// printf("Error copy to video memory.\n");
// return -1;
//}
// Free memory
if(cublasFree(K0cuda) != CUBLAS_STATUS_SUCCESS) {
printf("Error freeing video memory.\n");
return -1;
}
// CUDA shutdown
if(cublasShutdown() != CUBLAS_STATUS_SUCCESS) {
printf("CUBLAS shutdown error.\n");
return -1;
}
if(theSim != NULL) delete theSim;
return 0;
}

Answer 1

Memory can fragment, which means that you can still allocate multiple smaller blocks but not a single large block. Your videocard will obviously need some memory for its normal 2D task. If that happens to break the 128 MB into 2 blocks of almost 64MB, then you'd see this kind of failure.