netdev - Re: [PATCH openvswitch v3] netlink: Implement & enable memory mapped netlink i/o

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Date:	Wed, 04 Dec 2013 18:20:53 +0100
From:	Thomas Graf <tgraf@...hat.com>
To:	Ben Pfaff <blp@...ira.com>
CC:	jesse@...ira.com, dev@...nvswitch.org, netdev@...r.kernel.org,
	dborkman@...hat.com, ffusco@...hat.com, fleitner@...hat.com,
	xiyou.wangcong@...il.com
Subject: Re: [PATCH openvswitch v3] netlink: Implement & enable memory mapped
 netlink i/o

On 12/04/2013 05:33 PM, Ben Pfaff wrote:
> If I'm doing the calculations correctly, this mmaps 8 MB per ring-based
> Netlink socket on a system with 4 kB pages.  OVS currently creates one
> Netlink socket for each datapath port.  With 1000 ports (a moderate
> number; we sometimes test with more), that is 8 GB of address space.  On
> a 32-bit architecture that is impossible.  On a 64-bit architecture it
> is possible but it may reserve an actual 8 GB of RAM: OVS often runs
> with mlockall() since it is something of a soft real-time system (users
> don't want their packet delivery delayed to page data back in).
>
> Do you have any thoughts about this issue?

That's certainly a problem. I had the impression that the changes that
allow to consolidate multiple bridges to a single DP would minimize the
number of DPs used.

How about we limit the number of mmaped sockets to a configurable
maximum that defaults to 16 or 32?
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