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SubjectRe: [patch] mm: vmscan implement per-zone shrinkers
On Mon, Nov 15, 2010 at 09:50:36AM +0900, KOSAKI Motohiro wrote:
> > > @@ -1835,8 +1978,6 @@ static void shrink_zone(int priority, st
> > > break;
> > > }
> > >
> > > - sc->nr_reclaimed = nr_reclaimed;
> > > -
> > > /*
> > > * Even if we did not try to evict anon pages at all, we want to
> > > * rebalance the anon lru active/inactive ratio.
> > > @@ -1844,6 +1985,23 @@ static void shrink_zone(int priority, st
> > > if (inactive_anon_is_low(zone, sc))
> > > shrink_active_list(SWAP_CLUSTER_MAX, zone, sc, priority, 0);
> > >
> > > + /*
> > > + * Don't shrink slabs when reclaiming memory from
> > > + * over limit cgroups
> > > + */
> > > + if (sc->may_reclaim_slab) {
> > > + struct reclaim_state *reclaim_state = current->reclaim_state;
> > > +
> > > + shrink_slab(zone, sc->nr_scanned - nr_scanned,
> >
> > Doubtful calculation. What mean "sc->nr_scanned - nr_scanned"?
> > I think nr_scanned simply keep old slab balancing behavior.
>
> And per-zone reclaim can lead to new issue. On 32bit highmem system,
> theorically the system has following memory usage.
>
> ZONE_HIGHMEM: 100% used for page cache
> ZONE_NORMAL: 100% used for slab
>
> So, traditional page-cache/slab balancing may not work. I think following

Yes, in theory you are right. I guess in theory the same hole exists
if we have 0% page cache reclaimable globally, but this may be slightly
more likely to hit.


> new calculation or somethinhg else is necessary.
>
> if (zone_reclaimable_pages() > NR_SLAB_RECLAIMABLE) {
> using current calculation
> } else {
> shrink number of "objects >> reclaim-priority" objects
> (as page cache scanning calculation)
> }
>
> However, it can be separate this patch, perhaps.

I agree. In fact, perhaps the new calculation would work well in all
cases anyway, so maybe we should move away from making slab reclaim a
slave to pagecache reclaim.

Can we approach that in subsequent patches?

Thanks,
Nick



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