netdev - Re: issue with inflight pages from page

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Date:   Wed, 19 Apr 2023 18:10:43 +0200
From:   Jesper Dangaard Brouer <jbrouer@...hat.com>
To:     Eric Dumazet <edumazet@...gle.com>,
        Jesper Dangaard Brouer <jbrouer@...hat.com>
Cc:     brouer@...hat.com, Lorenzo Bianconi <lorenzo@...nel.org>,
        Jakub Kicinski <kuba@...nel.org>, netdev@...r.kernel.org,
        hawk@...nel.org, ilias.apalodimas@...aro.org, davem@...emloft.net,
        pabeni@...hat.com, bpf@...r.kernel.org,
        lorenzo.bianconi@...hat.com, nbd@....name,
        Toke Hoiland Jorgensen <toke@...hat.com>
Subject: Re: issue with inflight pages from page_pool


On 19/04/2023 16.18, Eric Dumazet wrote:
> On Wed, Apr 19, 2023 at 4:02 PM Jesper Dangaard Brouer
> <jbrouer@...hat.com> wrote:
> 
>> With TCP sockets (pipes etc) we can take care of closing the sockets
>> (and programs etc) to free up the SKBs (and perhaps wait for timeouts)
>> to make sure the page_pool shutdown doesn't hang.
> 
> This can not happen in many cases, like pages being now mapped to user
> space programs,
> or nfsd or whatever.
> 
> I think that fundamentally, page pool should handle this case gracefully.
> 
> For instance, when a TCP socket is closed(), user space can die, but
> many resources in the kernel are freed later.
> 
> We do not block a close() just because a qdisc decided to hold a
> buffer for few minutes.
> 

But page pool does handle this gracefully via scheduling a workqueue.

--Jesper