Re: [PATCH] vmscan: limit concurrent reclaimers in shrink_zone

[Rik van Riel]

On 12/11/2009 08:41 AM, Minchan Kim wrote:
> Hi, Larry.
>
> On Fri, Dec 11, 2009 at 9:07 PM, Larry Woodman<lwoodman@xxxxxxxxxx>  wrote:
> > Minchan Kim wrote:
> > > I like this. but why do you select default value as constant 8?
> > > Do you have any reason?
> > >
> > > I think it would be better to select the number proportional to NR_CPU.
> > > ex) NR_CPU * 2 or something.
> > >
> > > Otherwise looks good to me.
> > >
> > > Reviewed-by: Minchan Kim<minchan.kim@xxxxxxxxx>
> >
> > This is a per-zone count so perhaps a reasonable default is the number of
> > CPUs on the
> > NUMA node that the zone resides on ?
>
> For example, It assume one CPU per node.
> It means your default value is 1.
> On the CPU, process A try to reclaim HIGH zone.
> Process B want to reclaim NORMAL zone.
> But Process B can't enter reclaim path sincev throttle default value is 1
> Even kswap can't reclaim.

1) the value is per zone, so process B can go ahead

2) kswapd is always excempt from this limit, since
   there is only 1 kswapd per node anyway

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