netdev - Re: [RFC] folding socket->wq into struct socket

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Date:   Sun, 5 May 2019 18:59:43 +0100
From:   Al Viro <viro@...iv.linux.org.uk>
To:     David Miller <davem@...emloft.net>
Cc:     netdev@...r.kernel.org
Subject: Re: [RFC] folding socket->wq into struct socket

On Sun, May 05, 2019 at 10:04:21AM -0700, David Miller wrote:
> From: Al Viro <viro@...iv.linux.org.uk>
> Date: Thu, 2 May 2019 17:32:23 +0100
> 
> > it appears that we might take freeing the socket itself to the
> > RCU-delayed part, along with socket->wq.  And doing that has
> > an interesting benefit - the only reason to do two separate
> > allocation disappears.
> 
> I'm pretty sure we looked into RCU freeing the socket in the
> past but ended up not doing so.
> 
> I think it had to do with the latency in releasing sock related
> objects.
> 
> However, I might be confusing "struct socket" with "struct sock"

Erm...  the only object with changed release time is the memory
occupied by struct sock_alloc.  Currently:
final iput of socket
	schedule RCU-delayed kfree() of socket->wq
	kfree() of socket
With this change:
final iput of socket
	schedule RCU-delayed kfree() of coallocated socket and socket->wq

So it would have to be a workload where tons of sockets are created and
torn down, where RCU-delayed freeing of socket_wq is an inevitable evil,
but freeing struct socket_alloc itself must be done immediately, to
reduce the memory pressure.  Or am I misreading you?