netdev - Re: [RFC Patch] net: reserve ports for applications using fixed port numbers

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Message-Id: <201002042015.51092.opurdila@ixiacom.com>
Date:	Thu, 4 Feb 2010 20:15:51 +0200
From:	Octavian Purdila <opurdila@...acom.com>
To:	David Miller <davem@...emloft.net>
Cc:	amwang@...hat.com, linux-kernel@...r.kernel.org,
	eric.dumazet@...il.com, linux-rdma@...r.kernel.org,
	netdev@...r.kernel.org, nhorman@...driver.com,
	linux-sctp@...r.kernel.org
Subject: Re: [RFC Patch] net: reserve ports for applications using fixed port numbers

On Thursday 04 February 2010 19:41:10 you wrote:

> From: Octavian Purdila <opurdila@...acom.com>
> Date: Thu, 4 Feb 2010 14:44:01 +0200
> 
> > My concern is that we can have multiple applications that require a
> > fixed port and if those ports are significantly apart we will
> > decrease the port range available for connect. And that will hurt
> > the rate of which new connections can be opened.
> 
> I'm already uneasy about adding the simple check every time
> we loop around in the bind port allocator.
> 
> Adding an LSM hook to this spot?  I absolutely refuse to allow
> that, it will completely kill bind performance.
> 

I think Tetsuo was proposing the LSM hook, so I'll leave him the daunting task 
of convincing you of the benefit of that :) - I have no opinion on this due to 
massive lack of knowledge.

I was just proposing to use a discrete set of ports instead of a range. The 
check in the current patch:

int inet_is_reserved_local_port(int port)
{
       int min, max;

       inet_get_local_reserved_ports(&min, &max);
       if (min && max)
               return (port >= min && port <= max);
       return 0;
}

would become:

int inet_is_reserved_local_port(int port)
{
	if (test_bit(port, reserved_ports))
		return 1;
	return 0;
}

In theory it might be slower because of the reserved_ports bitmap will have a 
larger memory footprint than just a min/max, especially with random port 
allocation. But is this an issue in practice?
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