[SPDK] spdk_zmalloc error

Hi, 
 I meet a weird problem. The error below only happens in one machine of my cluster, but in other nodes, the program run successfully without bug.
 I try to build a memory pool, which consists of 256 buffers, each is 32M.
 Here is my code snippet. For a memory pool, it will execute many times.
----------------------------------------------
#define SPDK_PAGE_SIZE (4096)
#define SPDK_BUFFER_SIZE (32ull<<20)
 buffer_ = (char*)spdk_zmalloc(SPDK_BUFFER_SIZE, 
                                      SPDK_PAGE_SIZE, NULL, 
                                      SPDK_ENV_SOCKET_ID_ANY,
                                      SPDK_MALLOC_DMA);
if(buffer_ == nullptr){
fprintf(stderr, "%s:%d: SPDK allocate memory failed\n", __FILE__, __LINE__);
}
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I found that in some buffer allocations, the variable buffer_ after the spdk_zmalloc is still a nullptr. 
It makes the program throw error output.
I start up spdk enviroment with hugemem=16384, the total memory pool size 8GB.
SPDK vesion is v20.01


Could someone give me some comments? thanks.