netdev - Re: [PATCH] net: allow netdev_wait

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Date:	Fri, 30 Oct 2009 17:37:25 -0700
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	Benjamin LaHaise <bcrl@...et.ca>
Cc:	Eric Dumazet <eric.dumazet@...il.com>,
	Octavian Purdila <opurdila@...acom.com>,
	netdev@...r.kernel.org, Cosmin Ratiu <cratiu@...acom.com>
Subject: Re: [PATCH] net: allow netdev_wait_allrefs() to run faster

Benjamin LaHaise <bcrl@...et.ca> writes:

> On Fri, Oct 30, 2009 at 04:25:52PM -0700, Eric W. Biederman wrote:
>> I realized after sending the message that s_mode in sysfs_dirent is a
>> real size offense.  It is a 16bit field packed in between two longs.
>> So in practice it is possible to move the s_mode  up next to s_flags
>> and add a s_nlink after it both unsigned short and get a cheap sysfs_nlink.
>
> That doesn't work -- the number of directory entries can easily exceed 65535.  
> Current mid range hardware is good enough to terminate 100,000 network 
> interfaces on a single host.

On overflow you nlink becomes zero and you leave it there.  That is how
ondisk filesystems handle that case on directories, and find etc
knows how to deal.

>> Since I'm not quite ready to post my patches.  I will briefly
>> mention what I have in my queue and hopefully get things posted.
>> 
>> I have changes to make it so that sysfs never has to go from
>> the sysfs_dirent to the sysfs inode.  
>
> Ah, interesting.

I have to cleanup sysfs before I merge changes for supporting
multiple network namespaces.

>> I have changes to sys_sysctl() so that it becomes a filesystem lookup
>> under /proc/sys.  Which ultimately makes the code easier to maintain
>> and debug.
>
> That sounds like a much saner approach, but has the wrinkle that procfs can 
> be configured out.

So I will add the dependency.  There are very few serious users of sys_sysctl,
and all of them have been getting a deprecated interface warning every
time they use it for the last several years.

>> Now back to getting things forward ported and ready to post.
>
> I'm looking forward to those changes.  I've been ignoring procfs for the 
> time being by disabling the per-interface entries in the network stack, 
> but there is some desire to be able to enable rp_filter on a per-interface 
> radius config at runtime.  rp_filter has to be disabled across the board 
> on my access routers, as there are several places where assymetric routing 
> is used for performance reasons.

Just out of curiosity does the loose rp_filter mode work for you?

Eric
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