Re: [PATCH tty-next 5/5] tty: Halve flip buffer GFP_ATOMIC memoryconsumption

[Peter Hurley]

On 12/08/2013 08:01 PM, Greg Kroah-Hartman wrote:
> On Fri, Nov 22, 2013 at 12:09:58PM -0500, Peter Hurley wrote:
> > tty flip buffers use GFP_ATOMIC allocations for received data
> > which is to be processed by the line discipline. For each byte
> > received, an extra byte is used to indicate the error status of
> > that byte.
> >
> > Instead, if the received data is error-free, encode the entire
> > buffer without status bytes.
> >
> > Signed-off-by: Peter Hurley <peter@xxxxxxxxxxxxxxxxxx>
> > ---
> >   drivers/tty/tty_buffer.c | 45 +++++++++++++++++++++++++++++++++++----------
> >   include/linux/tty.h      |  4 ++++
> >   include/linux/tty_flip.h |  8 ++++++--
> >   3 files changed, 45 insertions(+), 12 deletions(-)
> >
> > diff --git a/drivers/tty/tty_buffer.c b/drivers/tty/tty_buffer.c
> > index 6a3620e..c4fe20e 100644
> > --- a/drivers/tty/tty_buffer.c
> > +++ b/drivers/tty/tty_buffer.c
> > @@ -100,6 +100,7 @@ static void tty_buffer_reset(struct tty_buffer *p, size_t size)
> >   	p->next = NULL;
> >   	p->commit = 0;
> >   	p->read = 0;
> > +	p->flags = 0;
> >   }
> >
> >   /**
> > @@ -230,31 +231,49 @@ void tty_buffer_flush(struct tty_struct *tty)
> >    *	tty_buffer_request_room		-	grow tty buffer if needed
> >    *	@tty: tty structure
> >    *	@size: size desired
> > + *	@flags: buffer flags if new buffer allocated (default = 0)
> >    *
> >    *	Make at least size bytes of linear space available for the tty
> >    *	buffer. If we fail return the size we managed to find.
> > + *
> > + *	Will change over to a new buffer if the current buffer is encoded as
> > + *	TTY_NORMAL (so has no flags buffer) and the new buffer requires
> > + *	a flags buffer.
> >    */
> > -int tty_buffer_request_room(struct tty_port *port, size_t size)
> > +int __tty_buffer_request_room(struct tty_port *port, size_t size, int flags)
> >   {
> >   	struct tty_bufhead *buf = &port->buf;
> >   	struct tty_buffer *b, *n;
> > -	int left;
> > +	int left, change;
> >
> >   	b = buf->tail;
> > -	left = b->size - b->used;
> > +	if (b->flags & TTYB_NORMAL)
> > +		left = 2 * b->size - b->used;
> > +	else
> > +		left = b->size - b->used;
> >
> > -	if (left < size) {
> > +	change = (b->flags & TTYB_NORMAL) && (~flags & TTYB_NORMAL);
> > +	if (change || left < size) {
> >   		/* This is the slow path - looking for new buffers to use */
> >   		if ((n = tty_buffer_alloc(port, size)) != NULL) {
> > +			n->flags = flags;
> >   			buf->tail = n;
> >   			b->commit = b->used;
> >   			smp_mb();
> >   			b->next = n;
> > -		} else
> > +		} else if (change)
> > +			size = 0;
> > +		else
> >   			size = left;
> >   	}
> >   	return size;
> >   }
> > +EXPORT_SYMBOL_GPL(__tty_buffer_request_room);
>
> Why are you exporting this?  There is no function prototype anywhere, so
> no one can even try to call it, it should just be static, right?

Yes, sorry. Thanks for catching this.

> I've applied the first 4 patches in this series, care to fix this one
> up?

Patch coming.
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