netdev - Re: [PATCH v2 net-next 3/8] net: cdc_ncm: inform usbnet when rx buffers are reduced

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Message-ID: <87mwdz8jy5.fsf@nemi.mork.no>
Date:	Fri, 30 May 2014 15:39:14 +0200
From:	Bjørn Mork <bjorn@...k.no>
To:	David Laight <David.Laight@...LAB.COM>
Cc:	"netdev\@vger.kernel.org" <netdev@...r.kernel.org>,
	"linux-usb\@vger.kernel.org" <linux-usb@...r.kernel.org>,
	Alexey Orishko <alexey.orishko@...il.com>,
	Oliver Neukum <oliver@...kum.org>,
	Enrico Mioso <mrkiko.rs@...il.com>,
	Lars Melin <larsm17@...il.com>, Peter Stuge <peter@...ge.se>,
	Greg Suarez <gsuarez@...thmicro.com>
Subject: Re: [PATCH v2 net-next 3/8] net: cdc_ncm: inform usbnet when rx buffers are reduced

David Laight <David.Laight@...LAB.COM> writes:

> From: Bjørn Mork
> ...
>> > Since you are now copying the data out of the URB's skb before
>> > passing the ethernet packet upstream, is there ever any real
>> > requirement to use a small rx_max? or ever change rx_max?
>> 
>> Yes.  usbnet doesn't currently recycle skbs.  Continuously allocating 32
>> kB skbs (or even 64 kB truesize, which is the current cdc_ncm worst
>> case) on memory constrained hosts is bound to fail eventually.
>
> Getting usbnet to recycle skb shouldn't be too hard - and will
> be an immediate gain for most of the drivers.

Yes.  This is one of those problems that really isn't that hard to
solve.  Until you start hitting all the corner cases...  But I'm sure it
is doable.

Anyway, it is not going to be part of this patch series, which is merely
touching the cdc_ncm minidriver within the existing usbnet framework.


Bjørn
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