linux-kernel - RE: [PATCH v1 3/3] usb: gadget: NCM: Stop RX TCP Bursts getting dropped.

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Date:	Thu, 12 Jun 2014 09:42:54 +0000
From:	David Laight <David.Laight@...LAB.COM>
To:	'Jim Baxter' <jim_baxter@...tor.com>,
	Eric Dumazet <eric.dumazet@...il.com>
CC:	Felipe Balbi <balbi@...com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	"linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Bjørn Mork <bjorn@...k.no>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: RE: [PATCH v1 3/3] usb: gadget: NCM: Stop RX TCP Bursts getting
 dropped.

From: Jim Baxter
> On 30/05/14 12:25, Jim Baxter wrote:
> > On 29/05/14 20:04, Eric Dumazet wrote:
> >> On Thu, 2014-05-29 at 18:12 +0100, Jim Baxter wrote:
> >>
> >> 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@...gle.com>
> >>
> >>
> >>
> >
> > Thank you, I will clarify the description.
> >
> > Jim
> >
> 
> Hi Eric,
> 
> Is this commit log more correct?
> 
> 
> This fixes a problem with dropped packets over 16k CDC-NCM
> when the connection is being heavily used.
> 
> The issue was that the extracted frames cloned from the
> received frame were consuming more memory than necessary
> due to the truesize being ~32KB instead of ~2KB, this
> meant there was a high chance of reaching the sk_rcvbuf
> limit.

s/due to/resulting in/

	David

> 
> Acked-by: Eric Dumazet <edumazet@...gle.com>
> Signed-off-by: Jim Baxter <jim_baxter@...tor.com>
> 
> Thank you,
> Jim