netdev - Re: [PATCH net-next 0/7] mptcp: do not block on subflow socket

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Message-Id: <20200517.123641.663719377645438432.davem@davemloft.net>
Date:   Sun, 17 May 2020 12:36:41 -0700 (PDT)
From:   David Miller <davem@...emloft.net>
To:     fw@...len.de
Cc:     netdev@...r.kernel.org, pabeni@...hat.com,
        mathew.j.martineau@...ux.intel.com, matthieu.baerts@...sares.net
Subject: Re: [PATCH net-next 0/7] mptcp: do not block on subflow socket

From: Florian Westphal <fw@...len.de>
Date: Sat, 16 May 2020 10:46:16 +0200

> This series reworks mptcp_sendmsg logic to avoid blocking on the subflow
> socket.
> 
> It does so by removing the wait loop from mptcp_sendmsg_frag helper.
> 
> In order to do that, it moves prerequisites that are currently
> handled in mptcp_sendmsg_frag (and cause it to wait until they are
> met, e.g. frag cache refill) into the callers.
> 
> The worker can just reschedule in case no subflow socket is ready,
> since it can't wait -- doing so would block other work items and
> doesn't make sense anyway because we should not (re)send data
> in case resources are already low.
> 
> The sendmsg path can use the existing wait logic until memory
> becomes available.
> 
> Because large send requests can result in multiple mptcp_sendmsg_frag
> calls from mptcp_sendmsg, we may need to restart the socket lookup in
> case subflow can't accept more data or memory is low.
> 
> Doing so blocks on the mptcp socket, and existing wait handling
> releases the msk lock while blocking.
> 
> Lastly, no need to use GFP_ATOMIC for extension allocation:
> extend __skb_ext_alloc with gfp_t arg instead of hard-coded ATOMIC and
> then relax the allocation constraints for mptcp case: those requests
> occur in process context.

Series applied, thanks Florian.