DPDK 19.11.5 Legacy Memory Design Query

[Dmitry Kozlyuk]

2022-09-23 11:20 (UTC+0000), Umakiran Godavarthi (ugodavar): 
> [Uma] :  Yes we are unmapping the entire range hoping all are free inside DPDK and DPDK heaps never use these pages.
> 
> Suppose we have 400 pages total free_hp, we want only 252 pages , so we reduce nr_pages to 252.
> 
> So we assume 253 to 400 inside DPDK are free as we nr_pages are made by my application as 252.
> 
> ms_idx = rte_fbarray_find_next_n_free(arr, 0, 2); -> 253 comes
> ms_check_idx = rte_fbarray_find_next_n_free(arr, 0, RTE_PTR_DIFF(RTE_PTR_ADD(msl->base_va, msl->len), addr)/msl->page_sz); -> 253 comes (should be same as above)
> ms_next_idx =  rte_fbarray_find_next_used(arr, ms_idx); -> This comes -1 as NO USED page is there (<0)
> 
> Hence we call unmap like -> munmap(addr, RTE_PTR_DIFF(RTE_PTR_ADD(msl->base_va, msl->len), addr));
> 
> Please let us know how to check in DPDK free heaps or FBARRAY that these pages we are freeing are really safe ? (253 to 400 unwanted pages by our application, other than above 3 checks)
> 
> If it’s not safe to free, how to inform DPDK to free those pages in FBARRAY and also clean up its heap list so that it never crashes !!

There still DPDK malloc internal structures that you cannot adjust.
I suggest going another way:
Instead of letting DPDK allocate all hugepages and unmapping some,
allow DPDK to allocate an absolute minimum (1 x 2MB page?)
and add all the rest you need via rte_extmem_*() API.

Why do you need legacy mode in the first place?
Looks like you're painfully trying to achieve the same result
that dynamic mode would give you automatically.