Re: [PATCH net-next v1 06/11] page_pool: Coordinate refill with memory providers

[Stanislav Fomichev <sdf.kernel@gmail.com>]

On 11/11, Björn Töpel wrote:
> Stanislav Fomichev <sdf.kernel@gmail.com> writes:
> 
> > On 11/10, Björn Töpel wrote:
> 
> >> diff --git a/include/net/netdev_rx_queue.h b/include/net/netdev_rx_queue.h
> >> index 989120cbf452..ca12cbf7b825 100644
> >> --- a/include/net/netdev_rx_queue.h
> >> +++ b/include/net/netdev_rx_queue.h
> >> @@ -33,6 +33,12 @@ struct netdev_rx_queue {
> >>  	struct pp_memory_provider_params mp_params;
> >>  	/* stamps the page pools of each queue allocation */
> >>  	u32				mp_gen;
> >> +	/* NAPI of the running queue, for memory provider wakeups. Set while
> >> +	 * mp_armed, and if the provider has a refill_done op. Written under
> >> +	 * the ops lock, read under RCU, see netif_mp_wake().
> >> +	 */
> >> +	struct napi_struct __rcu	*mp_napi;
> >> +	bool				mp_armed;
> >
> > The comment should explain why mp_napi != napi? (I do not understand why)
> 
> Fair. It's the same NAPI, with other rules. napi is the driver's
> association: read under the ops lock, and not cleared when the NAPI is
> deleted. Provider wakeups run without that lock, from socket syscalls
> and ->release_netmem().
> 
> mp_napi is an RCU copy, set only while the device is up and the queue
> isn't restarting, for providers with ->refill_done(). netif_napi_del()
> clears it before its grace period. Setting it also schedules the NAPI
> once, which replays wakeups lost while the queue was stopped. I'll put
> that in the comment.

And all this only to make sure that we are not recycling something from
the old pp into the new one? And reworking existing pointer to change/update
its lifetime is not gonna do it?