netdev - Re: issue with inflight pages from page

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Message-ID: <CANn89iJw==Y9fqhc0Xpau_aH=Uq7kSNv8=MywdUgTGbLZHoisQ@mail.gmail.com>
Date:   Wed, 19 Apr 2023 16:18:16 +0200
From:   Eric Dumazet <edumazet@...gle.com>
To:     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 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.