Re: [PATCH] USB: f_mass_storage: dynamic buffers for better alignment

[MichaÅ Nazarewicz]

> On Mon, Mar 15, 2010 at 08:20:08PM +0100, Micha?? Nazarewicz wrote:
> > Each buffer is 4 pages and there are two such buffers in struct
> > fsg_common therefore the size of the structure is 9 pages.
> >
> > I've been simply concerned about using kamlloc() for such big
> > structures so in the end decided to split it into 3 allocations.
> >
> > Maybe I'm overeating though?  Or maybe vmalloc() would solve those
> > problems?  But then again, vmalloc() could degrade DMA performance
> > on systems w/o scatter-gather.

On Mon, 15 Mar 2010 20:28:13 +0100, Felipe Balbi <me@xxxxxxxxxxxxxxx> wrote:
> I have no opinion anymore :-p
>
> I can only think about the devices I've been working on which would be a
> pain to allocate so much memory and would suffer if you use vmalloc()
> too, so both would be a no-no for me :-p

So here it is...  I think allocating buffers dynamically via kmalloc()
is the safest way. :)

> > 	bh = common->buffhds;
> > 	rc = -ENOMEM;
> > 	i = FSG_NUM_BUFFERS;
> > 	for(;;) {
> > 		bh->buf = kmalloc(FSG_BUFLEN, GFP_KERNEL);
> > 		if (unlikely(!bh->buf))
> > 			goto error_release;
> > 		if (!--i)
> > 			break;
> > 		bh->next = bh + 1;
> > 		++bh;
> > 	}
> > 	bh->next = common->buffhds;

> how about ?
>
> for (i = FSG_NUM_BUFFER; i; i--, ++bh) {
> 	bh->buf = kmalloc(FSG_BUFLEN, GFP_KERNEL);
> 	if (!bh->buf)
> 		goto error_release;
> }

bh->next cyclic buffer needs to be initialised.  Otherwise I'd stick
with what you've posted.

--
Best regards,                                           _     _
 .o. | Liege of Serenely Enlightened Majesty of       o' \,=./ `o
 ..o | Computer Science,  MichaÅ "mina86" Nazarewicz     (o o)
 ooo +---[mina86@xxxxxxxxxx]---[mina86@jabber.org]---ooO--(_)--Ooo--
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