netdev - Re: [GIT]: Networking

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Date:	Tue, 16 Jun 2009 15:38:32 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	David Miller <davem@...emloft.net>
CC:	mingo@...e.hu, alan@...rguk.ukuu.org.uk,
	torvalds@...ux-foundation.org, akpm@...ux-foundation.org,
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [GIT]: Networking

David Miller a écrit :
> From: Ingo Molnar <mingo@...e.hu>
> Date: Tue, 16 Jun 2009 12:11:32 +0200
> 
>> sure, here you go (i also added a stack dump, just in case it's some 
>> kernel-internal socket open):
>>
>>  [ifconfig:3516]: Creates X25 socket.
>>
>> so plain ifconfig. Part of the ~1.5 years old net-tools-1.60-84.fc8.
> 
> Ok, ifconfig seems to open one of every socket type when it starts up.
> That explains why an X25 socket is openned and then closed.
> 
> Now the question is why is the X25 socket released by a timer?  This
> should only happen if some socket memory is still pending in the
> socket buffers.
> 
> Wait, I know why this is triggering now.  It's Eric Dumazet's SKB
> accounting optimizations.
> 
> So, I'll fix the X25 timer bug.  It's always been there, but
> beforehand this deferred-via-timer x25 socket destruction path almost
> never triggers.  So we never saw it.  Now it happens every time.
> 
> Eric can you sniff around and see what you think about this unforseen
> (at least for me) consequence of your changes?  Socket layers that use
> the current sk_wmem_alloc/sk_rmem_alloc value at destroy time to
> determine if a socket can be killed immediately, or need to be killed
> later via timer, will always see that dummy one byte allocation you
> now put there.
> 
> Can you look into that?
> 
> Thanks.


Sure I can look if a layer uses sk_wmem_alloc as you describe.

(I take you refer to commit 2b85a34e911bf483c27cfdd124aeb1605145dc80 :
net: No more expensive sock_hold()/sock_put() on each tx)

So there is no impact for sk_rmem_alloc AFAIK

Thanks
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