Messages in this thread | | | Subject | Re: [PATCH 03/27] mm, vmscan: Move LRU lists to node | From | Vlastimil Babka <> | Date | Fri, 10 Jun 2016 20:00:52 +0200 |
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[+CC Michal Hocko]
On 06/09/2016 08:04 PM, Mel Gorman wrote: > This moves the LRU lists from the zone to the node and all related data > such as counters, tracing, congestion tracking and writeback tracking. > This is mostly a mechanical patch but note that it introduces a number > of anomalies. For example, the scans are per-zone but using per-node > counters. We also mark a node as congested when a zone is congested. This > causes weird problems that are fixed later but is easier to review. > > Signed-off-by: Mel Gorman <mgorman@techsingularity.net> > Acked-by: Johannes Weiner <hannes@cmpxchg.org>
> @@ -535,17 +525,21 @@ struct zone { > > enum zone_flags { > ZONE_RECLAIM_LOCKED, /* prevents concurrent reclaim */ > - ZONE_CONGESTED, /* zone has many dirty pages backed by > + ZONE_OOM_LOCKED, /* zone is in OOM killer zonelist */
This one has been zapped recently, looks like rebasing resurrected it.
> @@ -1455,13 +1455,22 @@ bool compaction_zonelist_suitable(struct alloc_context *ac, int order, > enum compact_result compact_result; > > /* > + * This over-estimates the number of pages available for > + * reclaim/compaction but walking the LRU would take too > + * long. The consequences are that compaction may retry > + * longer than it should for a zone-constrained allocation > + * request. > + */ > + available = pgdat_reclaimable_pages(zone->zone_pgdat);
I'm worried if "longer than it should" means "potentially forever", as the limit on retries in should_compact_retry() doesn't apply when this function returns true. Unless some later patches change that.
I'm starting to wonder if it's a good idea to give up per-zone LRU accounting, because we still have per-zone watermarks that we are trying to satisfy. How will we even recognize situation where a small zone is so depleted of LRU pages that it can't even reach its watermarks, causing a massive whole-node reclaim? Couldn't we have a combination of per-node lru with per-zone accounting?
> + > + /* > * Do not consider all the reclaimable memory because we do not > * want to trash just for a single high order allocation which > * is even not guaranteed to appear even if __compaction_suitable > * is happy about the watermark check. > */ > - available = zone_reclaimable_pages(zone) / order;
This removed the scaling by order. Accidentally I guess, as the comment is still there.
> available += zone_page_state_snapshot(zone, NR_FREE_PAGES); > + available = min(zone->managed_pages, available); > compact_result = __compaction_suitable(zone, order, alloc_flags, > ac_classzone_idx(ac), available); > if (compact_result != COMPACT_SKIPPED &&
[...]
> @@ -1826,7 +1827,7 @@ static int numamigrate_isolate_page(pg_data_t *pgdat, struct page *page) > } > > page_lru = page_is_file_cache(page); > - mod_zone_page_state(page_zone(page), NR_ISOLATED_ANON + page_lru, > + mod_node_page_state(page_zone(page)->zone_pgdat, NR_ISOLATED_ANON + page_lru,
This again, I won't point out further. But I think a page_node() (or page_pgdat()?) function is called for?
> @@ -3486,10 +3486,19 @@ should_reclaim_retry(gfp_t gfp_mask, unsigned order, > unsigned long available; > unsigned long reclaimable; > > - available = reclaimable = zone_reclaimable_pages(zone); > - available -= DIV_ROUND_UP(no_progress_loops * available, > + /* > + * This over-estimates the number of pages available for > + * reclaim but walking the LRU would take too long. The > + * consequences are that this may continue trying to > + * reclaim for zone-constrained allocations even if those > + * zones are already depleted. > + */ > + reclaimable = pgdat_reclaimable_pages(zone->zone_pgdat); > + reclaimable = min(zone->managed_pages, reclaimable); > + available = reclaimable - DIV_ROUND_UP(no_progress_loops * reclaimable, > MAX_RECLAIM_RETRIES); > available += zone_page_state_snapshot(zone, NR_FREE_PAGES); > + available = min(zone->managed_pages, available); > > /* > * Would the allocation succeed if we reclaimed the whole
This adds to my worries about per-node LRU accounting :/
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