linux-kernel - Re: [PATCH] nfs: fix congestion control -v4

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Date:	Fri, 26 Jan 2007 09:50:34 +0100
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Andrew Morton <akpm@...l.org>
Cc:	Trond Myklebust <trond.myklebust@....uio.no>,
	Christoph Lameter <clameter@....com>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org, pj@....com
Subject: Re: [PATCH] nfs: fix congestion control -v4

On Fri, 2007-01-26 at 09:00 +0100, Peter Zijlstra wrote:
> On Thu, 2007-01-25 at 21:02 -0800, Andrew Morton wrote:
> > On Thu, 25 Jan 2007 16:32:28 +0100
> > Peter Zijlstra <a.p.zijlstra@...llo.nl> wrote:
> > 
> > > +long congestion_wait_interruptible(int rw, long timeout)
> > > +{
> > > +	long ret;
> > > +	DEFINE_WAIT(wait);
> > > +	wait_queue_head_t *wqh = &congestion_wqh[rw];
> > > +
> > > +	prepare_to_wait(wqh, &wait, TASK_INTERRUPTIBLE);
> > > +	if (signal_pending(current))
> > > +		ret = -ERESTARTSYS;
> > > +	else
> > > +		ret = io_schedule_timeout(timeout);
> > > +	finish_wait(wqh, &wait);
> > > +	return ret;
> > > +}
> > > +EXPORT_SYMBOL(congestion_wait_interruptible);
> > 
> > I think this can share code with congestion_wait()?
> > 
> > static long __congestion_wait(int rw, long timeout, int state)
> > {
> > 	long ret;
> > 	DEFINE_WAIT(wait);
> > 	wait_queue_head_t *wqh = &congestion_wqh[rw];
> > 
> > 	prepare_to_wait(wqh, &wait, state);
> > 	ret = io_schedule_timeout(timeout);
> > 	finish_wait(wqh, &wait);
> > 	return ret;
> > }
> > 
> > long congestion_wait_interruptible(int rw, long timeout)
> > {
> > 	long ret = __congestion_wait(rw, timeout);
> > 
> > 	if (signal_pending(current))
> > 		ret = -ERESTARTSYS;
> > 	return ret;
> > }
> > 
> > it's only infinitesimally less efficient..
> 
> All the other _interruptible functions check signal_pending before
> calling schedule. Which seems to make sense since its called in a loop
> anyway, and if the loop condition turns false when interrupted you might
> as well just finish up instead of bailing out.
> 
> However if you'd rather see your version, who am I to object ;-)

ok, first wake up, then reply to emails :-)

How about this:

long congestion_wait_interruptible(int rw, long timeout)
{
	long ret;

	if (signal_pending(current))
		ret = -ERESTARTSYS;
	else
		ret = congestion_wait(rw, timeout);
	return ret;
}
EXPORT_SYMBOL(congestion_wait_interruptible);


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