Re: [PATCH 12/27] mm, vmscan: Make shrink_node decisions more node-centric

Vlastimil Babka
2016-06-16T13:35:23Z

On 06/09/2016 08:04 PM, Mel Gorman wrote:
> Earlier patches focused on having direct reclaim and kswapd use data that
> is node-centric for reclaiming but shrink_node() itself still uses too much
> zone information. This patch removes unnecessary zone-based information
> with the most important decision being whether to continue reclaim or
> not. Some memcg APIs are adjusted as a result even though memcg itself
> still uses some zone information.
>
> Signed-off-by: Mel Gorman <mgorman@techsingularity.net>

[...]

> @@ -2372,21 +2374,27 @@ static inline bool should_continue_reclaim(struct zone *zone,
> * inactive lists are large enough, continue reclaiming
> */
> pages_for_compaction = (2UL << sc->order);
> - inactive_lru_pages = node_page_state(zone->zone_pgdat, NR_INACTIVE_FILE);
> + inactive_lru_pages = node_page_state(pgdat, NR_INACTIVE_FILE);
> if (get_nr_swap_pages() > 0)
> - inactive_lru_pages += node_page_state(zone->zone_pgdat, NR_INACTIVE_ANON);
> + inactive_lru_pages += node_page_state(pgdat, NR_INACTIVE_ANON);
> if (sc->nr_reclaimed < pages_for_compaction &&
> inactive_lru_pages > pages_for_compaction)
> return true;
>
> /* If compaction would go ahead or the allocation would succeed, stop */
> - switch (compaction_suitable(zone, sc->order, 0, 0)) {
> - case COMPACT_PARTIAL:
> - case COMPACT_CONTINUE:
> - return false;
> - default:
> - return true;
> + for (z = 0; z <= sc->reclaim_idx; z++) {
> + struct zone *zone = &pgdat->node_zones[z];
> +
> + switch (compaction_suitable(zone, sc->order, 0, 0)) {

Using 0 for classzone_idx here was sort of OK when each zone was
reclaimed separately, as a Normal allocation not passing appropriate
classzone_idx (and thus subtracting lowmem reserve from free pages)
means that a false COMPACT_PARTIAL (or COMPACT_CONTINUE) could be
returned for e.g. DMA zone. It means a premature end of reclaim for this
single zone, which is relatively small anyway, so no big deal (and we
might avoid useless over-reclaim, when even reclaiming everything
wouldn't get us above the lowmem_reserve).

But in node-centric reclaim, such premature "return false" from a DMA
zone stops reclaiming the whole node. So I think we should involve the
real classzone_idx here.

> + case COMPACT_PARTIAL:
> + case COMPACT_CONTINUE:
> + return false;
> + default:
> + /* check next zone */
> + ;
> + }
> }
> + return true;
> }
>