Wu Fengguang <[email protected]> wrote:
>
> 850 sc->nr_to_reclaim = sc->swap_cluster_max;
> 851
> 852 while (nr_active || nr_inactive) {
> //...
> 860 if (nr_inactive) {
> 861 sc->nr_to_scan = min(nr_inactive,
> 862 (unsigned long)sc->swap_cluster_max);
> 863 nr_inactive -= sc->nr_to_scan;
> 864 shrink_cache(zone, sc);
> 865 if (sc->nr_to_reclaim <= 0)
> 866 break;
> 867 }
> 868 }
>
> Line 843 is the core of the scan balancing logic:
>
> priority 12 11 10
>
> On each call nr_scan_inactive is increased by:
> DMA(2k pages) +1 +2 +3
> Normal(64k pages) +17 +33 +65
>
> Round it up to SWAP_CLUSTER_MAX=32, we get (scan batches/accumulate rounds):
> DMA 1/32 1/16 2/11
> Normal 2/2 2/1 3/1
> DMA:Normal ratio 1:32 1:32 2:33
>
> This keeps the scan rate roughly balanced(i.e. 1:32) in low vm pressure.
>
> But lines 865-866 together with line 846 make most shrink_zone() invocations
> only run one batch of scan. The numbers become:
True. Need to go into a huddle with the changelogs, but I have a feeling
that lines 865 and 866 aren't very important. What happens if we remove
them?
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