netdev - Re: setsockopt()

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Message-ID: <1e41a3230807081707rcdb7ed6o91ff6e7d00aaa70b@mail.gmail.com>
Date:	Tue, 8 Jul 2008 17:07:45 -0700
From:	"John Heffner" <johnwheffner@...il.com>
To:	"Jim Rees" <rees@...ch.edu>
Cc:	netdev@...r.kernel.org, aglo@...i.umich.edu, shemminger@...tta.com,
	bfields@...ldses.org
Subject: Re: setsockopt()

On Tue, Jul 8, 2008 at 4:51 PM, Jim Rees <rees@...ch.edu> wrote:
> John Heffner wrote:
>
>  I actually like your idea for a "soft"
>  SO_SNDBUF -- ask the kernel for at least that much, but let it
>  autotune higher if needed.  This is almost trivial to implement --
>  it's the same as SO_SNDBUF but don't set the sock sndbuf lock.
>
> Which brings me to another issue.  The nfs server doesn't call
> sock_setsockopt(), it diddles sk_sndbuf and sk_rcvbuf directly, so as to get
> around the max socket buf limit.  I don't like this.  If this is a legit
> thing to do, there should be an api.
>
> I'm thinking we need a sock_set_min_bufsize(), where the values passed in
> are minimums, subject to autotuning, and maybe are not limited by the max.
> It would, as you say, just set sk_sndbuf and sk_rcvbuf without setting the
> corresponding flags SOCK_SNDBUF_LOCK and SOCK_RCVBUF_LOCK.
>
> Would this do the trick, or is there a danger that autotuning would reduce
> the buffer sizes below the given minimum?  If so, we might need
> sk_min_rcvbuf or something like that.


TCP buffer sizes will only be pulled back if the system runs into the
global tcp memory limits (sysctl_tcp_mem).  I think this is correct
behavior regardless of the requested value.

  -John
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