Re: [PATCH 3/5] vmscan: Force kswapd to take notice faster when high-order watermarks are being hit

[Mel Gorman <mel@csn.ul.ie>]

On Fri, Oct 23, 2009 at 10:52:42AM -0700, Vincent Li wrote:
> 
> I trimmed out most CC recipients while replying this message cause I don't 
> want to fill out everybody's mailbox with my noise. :-)
> 

Sure.

> On Thu, 22 Oct 2009, Mel Gorman wrote:
> 
> > When a high-order allocation fails, kswapd is kicked so that it reclaims
> > at a higher-order to avoid direct reclaimers stall and to help GFP_ATOMIC
> > allocations. Something has changed in recent kernels that affect the timing
> > where high-order GFP_ATOMIC allocations are now failing with more frequency,
> > particularly under pressure. This patch forces kswapd to notice sooner that
> > high-order allocations are occuring.
> > 
> > Signed-off-by: Mel Gorman <mel@csn.ul.ie>
> > ---
> >  mm/vmscan.c |    9 +++++++++
> >  1 files changed, 9 insertions(+), 0 deletions(-)
> > 
> > diff --git a/mm/vmscan.c b/mm/vmscan.c
> > index 64e4388..cd68109 100644
> > --- a/mm/vmscan.c
> > +++ b/mm/vmscan.c
> > @@ -2016,6 +2016,15 @@ loop_again:
> >  					priority != DEF_PRIORITY)
> >  				continue;
> >  
> > +			/*
> > +			 * Exit quickly to restart if it has been indicated
>                            ^^^^^^^^^^^^^^^^^^^^^^^ meaning exit to 
> lable loop_again in balance_pgdat ?
> 

I think you misunderstand. What I mean is that this function should exit
quickly so the whole kswapd loop in kswapd() starts all over again. I'm
not referring to any label.

> > +			 * that higher orders are required
> > +			 */
> > +			if (pgdat->kswapd_max_order > order) {
> > +				all_zones_ok = 1;
> > +				goto out;
> > +			}
> 
> If exit quickly to loop_again, shouldn't all_zones_ok be 0 instead of 1?
> 

I don't want it to go to loop_again. I want kswapd to start from the
beginning using the higher order.

> > +
> >  			if (!zone_watermark_ok(zone, order,
> >  					high_wmark_pages(zone), end_zone, 0))
> >  				all_zones_ok = 0;
> > -- 
> > 1.6.3.3
> > 
> 
> Thanks for clarification in advance.
> 

I hope this helps.

-- 
Mel Gorman
Part-time Phd Student                          Linux Technology Center
University of Limerick                         IBM Dublin Software Lab

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