linux-kernel - Re: [PATCH v3 1/3] net/usb/r815x: replace USB buffer from stack to DMA-able

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Message-Id: <20130730.113329.1450325193505423812.davem@davemloft.net>
Date:	Tue, 30 Jul 2013 11:33:29 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	gregkh@...uxfoundation.org
Cc:	hayeswang@...ltek.com, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-usb@...r.kernel.org,
	nic_swsd@...ltek.com
Subject: Re: [PATCH v3 1/3] net/usb/r815x: replace USB buffer from stack to
 DMA-able

From: Greg KH <gregkh@...uxfoundation.org>
Date: Tue, 30 Jul 2013 07:00:59 -0700

> This call is so slow, you can afford to make a call to kmalloc for the
> data, as it sure just did for other structures it needed :)

I told him to implement things this way, to avoid calling kmalloc every
single register access.

Using kmalloc all the time makes the access fragile, since a badly timed
call during high memory pressure can fail.

I'd rather the potential failure happen at one time, probe time.

In any event, Ming Lei has suggested using usbnet_{read,write}_cmd()
instead, which sounds like a good solution to this problem.
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