linux-kernel - Re: bluetooth drivers : kmalloc to kzalloc conversion

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Date:	Sun, 17 Sep 2006 22:38:27 -0400
From:	Dmitry Torokhov <dtor@...ightbb.com>
To:	Om Narasimhan <om.turyx@...il.com>
Cc:	linux-kernel@...r.kernel.org, kernel-janitors@...ts.osdl.org,
	bluez-devel@...ts.sf.net
Subject: Re: bluetooth drivers : kmalloc to kzalloc conversion

On Sunday 17 September 2006 22:24, Om Narasimhan wrote:
> On 9/17/06, Dmitry Torokhov <dtor@...ightbb.com> wrote:
> > On Sunday 17 September 2006 20:54, Om Narasimhan wrote:
> > > --- a/drivers/bluetooth/hci_usb.c
> > > +++ b/drivers/bluetooth/hci_usb.c
> > > @@ -147,10 +147,9 @@ static struct usb_device_id blacklist_id
> > >
> > > static struct _urb *_urb_alloc(int isoc, gfp_t gfp)
> > > {
> > > -struct _urb *_urb = kmalloc(sizeof(struct _urb) +
> > > +struct _urb *_urb = kzalloc(sizeof(struct _urb) +
> > > sizeof(struct usb_iso_packet_descriptor) * isoc, gfp);
> > > if (_urb) {
> > > -memset(_urb, 0, sizeof(*_urb));
> > > usb_init_urb(&_urb->urb);
> > > }
> > > return _urb;
> > >
> >
> > Note that only beginning if the aloocated memory was zeroed in original
> > code; your patch may introduce slowdowns.
> Would it? I thought memset() uses block move operation which doesn't
> scale linearly.

Well, the old code was zeroing sizeof(struct _urb) bytes while yours is
zeroing sizeof(struct _urb) + X so it will definitely take more time.

> And, usb_init_urb() calls memset() anyway, so the previously existed
> memset() was superfluous.
> 

It only clears part of struct _urb. Note that "stuct _urb" and "struct urb"
are 2 different structures.

-- 
Dmitry
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