Re: [PATCH 01/10] mm: vmscan: Limit the number of pages kswapd reclaimsat each priority

[Simon Jeons]

Hi Mel,
On 03/19/2013 05:55 PM, Mel Gorman wrote:
> On Tue, Mar 19, 2013 at 07:53:16AM +0800, Simon Jeons wrote:
> > Hi Mel,
> > On 03/17/2013 09:04 PM, Mel Gorman wrote:
> > > The number of pages kswapd can reclaim is bound by the number of pages it
> > > scans which is related to the size of the zone and the scanning priority. In
> > > many cases the priority remains low because it's reset every SWAP_CLUSTER_MAX
> > > reclaimed pages but in the event kswapd scans a large number of pages it
> > > cannot reclaim, it will raise the priority and potentially discard a large
> > > percentage of the zone as sc->nr_to_reclaim is ULONG_MAX. The user-visible
> > > effect is a reclaim "spike" where a large percentage of memory is suddenly
> > > freed. It would be bad enough if this was just unused memory but because
> > Since there is nr_reclaimed >= nr_to_reclaim check if priority is
> > large than DEF_PRIORITY in shrink_lruvec, how can a large percentage
> > of memory is suddenly freed happen?
> Because of the priority checks made in get_scan_count(). Patch 5 has
> more detail on why this happens.
But nr_reclaim >= nr_to_reclaim check in function shrink_lruvec is after 
scan each evictable lru, so if priority == 0, still scan the whole world.
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