From mboxrd@z Thu Jan  1 00:00:00 1970
From: Jim Baxter <jim_baxter@mentor.com>
Subject: Re: [PATCH v1 3/3] usb: gadget: NCM: Stop RX TCP Bursts getting dropped.
Date: Fri, 30 May 2014 12:25:48 +0100
Message-ID: <53886ABC.8030303@mentor.com>
References: <Jim Baxter <jim_baxter@mentor.com>	 <1401383543-10181-1-git-send-email-jim_baxter@mentor.com>	 <1401383543-10181-4-git-send-email-jim_baxter@mentor.com> <1401390263.3645.51.camel@edumazet-glaptop2.roam.corp.google.com>
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Cc: Felipe Balbi <balbi@ti.com>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	<linux-usb@vger.kernel.org>, <linux-kernel@vger.kernel.org>,
	=?UTF-8?B?QmrDuA==?= =?UTF-8?B?cm4gTW9yaw==?= <bjorn@mork.no>,
	David Laight <David.Laight@ACULAB.COM>,
	<netdev@vger.kernel.org>
To: Eric Dumazet <eric.dumazet@gmail.com>
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On 29/05/14 20:04, Eric Dumazet wrote:
> On Thu, 2014-05-29 at 18:12 +0100, Jim Baxter wrote:
>> This fixes a problem with dropped packets over 16k CDC-NCM
>> when the connection is being heavily used.
>>
>> The issue was that the skb truesize for the unpacked NCM
>> packets was too high after they were cloned from the 16k
>> skb, this lead to the potential memory calculated by the
>> Kernel running out of memory earlier then it should.
>>
>> Signed-off-by: Jim Baxter <jim_baxter@mentor.com>
>> ---
> 
> Note the patch is OK, but changelog a bit misleading ;)
> 
> Kernel was not running out of memory, because truesize was correct.
> 
> The problem here is that a frame was consuming more kernel memory than
> really needed, so chances of hitting socket sk_rcvbuf limit was high.
> 
> BTW :
> #define NTB_OUT_SIZE              16384
> 
> alloc_skb(size) ->
> 	kmalloc(16384 + sizeof(struct skb_shared_info)) ->
> 		roundup() => 32768
> 
> So truesize of the skb was infact ~32KB, which is really insane indeed.
> After your patch, its back to ~2KB
> 
> Acked-by: Eric Dumazet <edumazet@google.com>
> 
> 
> 

Thank you, I will clarify the description.

Jim