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

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Date:	Fri, 26 Jan 2007 09:00:12 +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 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 ;-)

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