Direct Mem Pool vs Indirect mem pool creation

[Thomas Monjalon]

01/09/2023 14:47, omer yamac:
> Hello,
> 
> I need clarification while creating direct/indirect buffers for mbuf. I
> couldn't find exact documentation, and I just looked over the fragmentation
> test case and saw that two pools were created. One is a
> direct pool, and the other is an indirect pool. Here are the methods to
> create pools:
> direct_pool = rte_pktmbuf_pool_create("FRAG_D_MBUF_POOL",
>                           NUM_MBUFS, BURST, 0,
>                           RTE_MBUF_DEFAULT_BUF_SIZE,
>                           SOCKET_ID_ANY);
> indirect_pool = rte_pktmbuf_pool_create("FRAG_I_MBUF_POOL",
>                         NUM_MBUFS, BURST, 0,
>                         0, SOCKET_ID_ANY)
> 
> I couldn't see the exact difference. Just the "data_room_size" parameter is
> different. If this parameter is 0, then is the pool indirect?

A pool is neither direct or indirect, it is just a pool of buffers
with a defined size for all buffers of a pool.
You are free to create any pool for your needs.

Now if you create a pool of buffers with size 0,
we can expect you will save some data elsewhere,
using rte_pktmbuf_attach_extbuf() for instance.

More explanations can be found in the doc:
https://doc.dpdk.org/guides/prog_guide/mbuf_lib.html#direct-and-indirect-buffers