netdev - Re: [net-next PATCH v2 1/2] page_pool: do not release pool until inflight == 0.

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Message-ID: <20191114222753.03e50613@carbon>
Date:   Thu, 14 Nov 2019 22:27:53 +0100
From:   Jesper Dangaard Brouer <brouer@...hat.com>
To:     Jonathan Lemon <jonathan.lemon@...il.com>
Cc:     <netdev@...r.kernel.org>, <davem@...emloft.net>,
        <kernel-team@...com>, <ilias.apalodimas@...aro.org>,
        brouer@...hat.com
Subject: Re: [net-next PATCH v2 1/2] page_pool: do not release pool until
 inflight == 0.

On Thu, 14 Nov 2019 08:37:14 -0800
Jonathan Lemon <jonathan.lemon@...il.com> wrote:

> The page pool keeps track of the number of pages in flight, and
> it isn't safe to remove the pool until all pages are returned.
> 
> Disallow removing the pool until all pages are back, so the pool
> is always available for page producers.

I like this patch.
 
> Make the page pool responsible for its own delayed destruction
> instead of relying on XDP, so the page pool can be used without
> the xdp memory model.
> 
> When all pages are returned, free the pool and notify xdp if the
> pool is registered with the xdp memory system.  Have the callback
> perform a table walk since some drivers (cpsw) may share the pool
> among multiple xdp_rxq_info.
> 
> Note that the increment of pages_state_release_cnt may result in
> inflight == 0, releasing the pool.

Maybe we can just do the atomic_inc_return trick, and this patch can
itself can go in.

Alternative is to release the pool via RCU, like the xa
structure is freed via RCU (which have a pointer to the pool).


> Fixes: d956a048cd3f ("xdp: force mem allocator removal and periodic warning")
> Signed-off-by: Jonathan Lemon <jonathan.lemon@...il.com>
> ---

-- 
Best regards,
  Jesper Dangaard Brouer
  MSc.CS, Principal Kernel Engineer at Red Hat
  LinkedIn: http://www.linkedin.com/in/brouer