netdev - Re: [PATCH net-next 0/3] rxrpc: Allow more calls to same peer

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Date:   Tue, 08 Sep 2020 20:18:38 -0700 (PDT)
From:   David Miller <davem@...emloft.net>
To:     dhowells@...hat.com
Cc:     netdev@...r.kernel.org, linux-afs@...ts.infradead.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH net-next 0/3] rxrpc: Allow more calls to same peer

From: David Howells <dhowells@...hat.com>
Date: Tue, 08 Sep 2020 21:50:51 +0100

> Here are some development patches for AF_RXRPC that allow more simultaneous
> calls to be made to the same peer with the same security parameters.  The
> current code allows a maximum of 4 simultaneous calls, which limits the afs
> filesystem to that many simultaneous threads.  This increases the limit to
> 16.
> 
> To make this work, the way client connections are limited has to be changed
> (incoming call/connection limits are unaffected) as the current code
> depends on queuing calls on a connection and then pushing the connection
> through a queue.  The limit is on the number of available connections.
> 
> This is changed such that there's a limit[*] on the total number of calls
> systemwide across all namespaces, but the limit on the number of client
> connections is removed.
> 
> Once a call is allowed to proceed, it finds a bundle of connections and
> tries to grab a call slot.  If there's a spare call slot, fine, otherwise
> it will wait.  If there's already a waiter, it will try to create another
> connection in the bundle, unless the limit of 4 is reached (4 calls per
> connection, giving 16).
> 
> A number of things throttle someone trying to set up endless connections:
> 
>  - Calls that fail immediately have their conns deleted immediately,
> 
>  - Calls that don't fail immediately have to wait for a timeout,
> 
>  - Connections normally get automatically reaped if they haven't been used
>    for 2m, but this is sped up to 2s if the number of connections rises
>    over 900.  This number is tunable by sysctl.
> 
> 
> [*] Technically two limits - kernel sockets and userspace rxrpc sockets are
>     accounted separately.
> 
> The patches are tagged here:
> 
> 	git://git.kernel.org/pub/scm/linux/kernel/git/dhowells/linux-fs.git
> 	rxrpc-next-20200908

Pulled, thanks David.