Examples to use both FSDAX permanent memory and normal DRAM

[jesHrz]

Details

I'd like to use a hybrid memory pool simultaneously, where I allocate memory either from permanent memory from the FSDAX device or the normal DRAM from anonymous mapping.

I found that libmemkind meets my requirement because I can specify the different allocator via struct memkind in memkind_malloc.
Unfortunately, libmemkind is deprecated now...

I am wondering if I could find the same usage example from UMF as libmemkind does?

[vinser52]

Hi @jesHrz,

UMF is positioned as a replacement for Memkind. While UMF does not provide 1:1 API matching it is targeted to support Memkind use cases.

Could you please describe your use case precisely? What do you mean by “use a hybrid memory pool simultaneously”?

[jesHrz]

Hi @jesHrz,

UMF is positioned as a replacement for Memkind. While UMF does not provide 1:1 API matching it is targeted to support Memkind use cases.

Could you please describe your use case precisely? What do you mean by “use a hybrid memory pool simultaneously”?

Thanks a lot.

Actually, the hybrid memory pool means some objects are allocated from the DRAM and some objects are allocated from the PM.

Here is a simple example for my use case.

void *allocate_from_pm(size_t size)
{
    // allocate from persistent memory via UMF
}

void *allocate_from_dram(size_t size)
{
    // allocate from DRAM via UMF
}

int main() {
    int N = 100, M = 200;
    int *array_a = (int *)allocate_from_dram(sizeof(int) * N);
    int *array_b = (int *)allocate_from_pm(sizeof(int) * M);
    
    // access array_a and array_b

    free(array_a);
    free(array_b);
}

[ldorau]

Hi @jesHrz, I have just added to UMF the support for FSDAX (#746). In order to handle FSDAX, the file memory provider with the memory visibility mode parameter set to UMF_MEM_MAP_SYNC must be used. I am currently working on the example using both FSDAX permanent memory and normal DRAM, as you need. I will keep you updated. Please stay tuned.

[ldorau]

I have submitted the PR #750 with this example.

[jesHrz]

Hi @ldorau , much thanks for your effort!

BTW, I also want to know if UMF can automatically detect which pool a pointer is allocated from. since memkind can free a pointer with an unknown kind (memkind_free(NULL, ptr)).

[ldorau]

Hi @ldorau , much thanks for your effort!

BTW, I also want to know if UMF can automatically detect which pool a pointer is allocated from. since memkind can free a pointer with an unknown kind (memkind_free(NULL, ptr)).

Yes, there is the function:

///
/// @brief Retrieve memory pool associated with a given ptr. Only memory allocated
///        with the usage of a memory provider is being tracked.
/// @param ptr pointer to memory belonging to a memory pool
/// @return Handle to a memory pool that contains ptr or NULL if pointer does not belong to any UMF pool.
///
umf_memory_pool_handle_t umfPoolByPtr(const void *ptr);

[jesHrz]

It is actually what I want, thanks!

[ldorau]

Hi @jesHrz, the "Add dram_and_fsdax example" #750 has already been merged upstream.