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

From: Ivan Khoronzhuk
Date: Tue Jul 02 2019 - 14:58:55 EST

On Tue, Jul 02, 2019 at 08:29:07PM +0200, Jesper Dangaard Brouer wrote:
On Tue, 2 Jul 2019 18:21:13 +0300
Ivan Khoronzhuk <ivan.khoronzhuk@xxxxxxxxxx> wrote:

On Tue, Jul 02, 2019 at 05:10:29PM +0200, Jesper Dangaard Brouer wrote:
>On Tue, 2 Jul 2019 17:56:13 +0300
>Ivan Khoronzhuk <ivan.khoronzhuk@xxxxxxxxxx> wrote:
>> On Tue, Jul 02, 2019 at 04:52:30PM +0200, Jesper Dangaard Brouer wrote:
>> >On Tue, 2 Jul 2019 17:44:27 +0300
>> >Ivan Khoronzhuk <ivan.khoronzhuk@xxxxxxxxxx> wrote:
>> >
>> >> 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.
>> >
>> >I don't understand what you are saying.
>> >
>> >Do you approve this patch, or do you reject this patch?
>> >
>> It's not reject, it's proposition to use both, XDP and page pool patches,
>> each having its goal.
>Just to be clear, if you want this patch to get accepted you have to
>reply with your Signed-off-by (as I wrote).
>Maybe we should discuss it in another thread, about why you want two
>solutions to the same problem.

If it solves same problem I propose to reject this one and use this:

No, I propose using this one, and rejecting the other one.

There is at least several arguments against this one (related (2) purpose)

It allows:
- avoid changes to page_pool/mlx5/netsec
- save not only allocator obj but allocator "page/buffer flush"
- buffer flush can be present not only in page_pool but for other allocators
that can behave differently and not so simple solution.
- to not limit cpsw/(potentially others) to use "page_pool" allocator only

This patch better leave also, as it simplifies error path for page_pool and
have more error prone usage comparing with existent one.

Please, don't limit cpsw and potentially other drivers to use only
page_pool it can be zca or etc... I don't won't to modify each allocator.
I propose to add both as by fact they solve different problems with common

Ivan Khoronzhuk