Re: [PATCH] net: core: page_pool: add user refcnt and reintroduce page_pool_destroy

From: Ivan Khoronzhuk
Date: Tue Jul 02 2019 - 10:44:36 EST

On Tue, Jul 02, 2019 at 04:31:39PM +0200, Jesper Dangaard Brouer wrote:
From: Ivan Khoronzhuk <ivan.khoronzhuk@xxxxxxxxxx>

Jesper recently removed page_pool_destroy() (from driver invocation) and
moved shutdown and free of page_pool into xdp_rxq_info_unreg(), in-order to
handle in-flight packets/pages. This created an asymmetry in drivers
create/destroy pairs.

This patch add page_pool user refcnt and reintroduce page_pool_destroy.
This serves two purposes, (1) simplify drivers error handling as driver now
drivers always calls page_pool_destroy() and don't need to track if
xdp_rxq_info_reg_mem_model() was unsuccessful. (2) allow special cases
where a single RX-queue (with a single page_pool) provides packets for two
net_device'es, and thus needs to register the same page_pool twice with two
xdp_rxq_info structures.

As I tend to use xdp level patch there is no more reason to mention (2) case
here. XDP patch serves it better and can prevent not only obj deletion but also
pool flush, so, this one patch I could better leave only for (1) case.

Ivan Khoronzhuk