Re: DPDK 19.11.5 Legacy Memory Design Query

[Dmitry Kozlyuk <dmitry.kozliuk@gmail.com>]

Hi Umakiran,

> From: Umakiran Godavarthi (ugodavar) <ugodavar@cisco.com>
> Date: Wednesday, 14 September 2022 at 1:00 PM
[...]
>   1.  Then we go to DPDK Memory segment list walkthrough and for each FBARRAY , we find the used pages by DPDK and unmap the remaining pages by below code (Idea is to free the huge pages taken by DPDK process virtual memory) -> Free_HP will be 0 then, as X pages are used by DPDK and all unnecessary pages are freed in this step)
> Sample Code of 4 :
> 
>               rte_memseg_list_walk_thread_unsafe(dpdk_find_and_free_unused, NULL); ->DPDK_FIND_AND_FREE_UNUSED is called for each Memory segment list (FBARRAY pointer is derived from MSL like below)
> 
>               dpdk_find_and_free_unused(const struct rte_memseg_list *msl,
>                                           void *arg UNUSED)
>                {
>                       Int ms_idx;
>                        arr = (struct rte_fbarray *) &msl->memseg_arr;
> 
>                         /*
>                          * use size of 2 instead of 1 to find the next free slot but
>                         * not hole.
>                         */
>                      ms_idx = rte_fbarray_find_next_n_free(arr, 0, 2);
> 
>                      if (ms_idx >= 0) {
>                          addr = RTE_PTR_ADD(msl->base_va, ms_idx * msl->page_sz);
>                             munmap(addr, RTE_PTR_DIFF(RTE_PTR_ADD(msl->base_va, msl->len), addr));
>                       }
>                }

You unmap memory, but you do not maintain DPDK memory management structures,
that is, DPDK does not know that this page is no longer usable.
Probably this is the reason for the crash.
You could print regions you're unmapping and the segfault address to confirm.