Re: [patch v2] mm, vmscan: avoid thrashing anon lru when free + file is low
From: David Rientjes <rientjes@google.com>
Date: 2017-05-03 22:52:16
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On Wed, 3 May 2017, Michal Hocko wrote:
quoted hunk ↗ jump to hunk
diff --git a/mm/vmscan.c b/mm/vmscan.c index 24efcc20af91..f3ec8760dc06 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c@@ -2113,16 +2113,14 @@ static void get_scan_count(struct lruvec *lruvec, struct mem_cgroup *memcg, u64 denominator = 0; /* gcc */ struct pglist_data *pgdat = lruvec_pgdat(lruvec); unsigned long anon_prio, file_prio; - enum scan_balance scan_balance; + enum scan_balance scan_balance = SCAN_FILE; unsigned long anon, file; unsigned long ap, fp; enum lru_list lru; /* If we have no swap space, do not bother scanning anon pages. */ - if (!sc->may_swap || mem_cgroup_get_nr_swap_pages(memcg) <= 0) { - scan_balance = SCAN_FILE; + if (!sc->may_swap || mem_cgroup_get_nr_swap_pages(memcg) <= 0) goto out; - } /* * Global reclaim will swap to prevent OOM even with no@@ -2131,10 +2129,8 @@ static void get_scan_count(struct lruvec *lruvec, struct mem_cgroup *memcg, * using the memory controller's swap limit feature would be * too expensive. */ - if (!global_reclaim(sc) && !swappiness) { - scan_balance = SCAN_FILE; + if (!global_reclaim(sc) && !swappiness) goto out; - } /* * Do not apply any pressure balancing cleverness when the
Good as a cleanup so far.
quoted hunk ↗ jump to hunk
@@ -2147,8 +2143,9 @@ static void get_scan_count(struct lruvec *lruvec, struct mem_cgroup *memcg, } /* - * Prevent the reclaimer from falling into the cache trap: as - * cache pages start out inactive, every cache fault will tip + * We usually want to bias page cache reclaim over anonymous + * memory. Prevent the reclaimer from falling into the cache trap: + * as cache pages start out inactive, every cache fault will tip * the scan balance towards the file LRU. And as the file LRU * shrinks, so does the window for rotation from references. * This means we have a runaway feedback loop where a tiny
I think Minchan made a good point earlier about anon being more likely to be working set since it is mapped, but this may be a biased opinion coming from me since I am primarily concerned with malloc.
quoted hunk ↗ jump to hunk
@@ -2173,26 +2170,24 @@ static void get_scan_count(struct lruvec *lruvec, struct mem_cgroup *memcg, total_high_wmark += high_wmark_pages(zone); } - if (unlikely(pgdatfile + pgdatfree <= total_high_wmark)) { + if (unlikely(pgdatfile + pgdatfree <= total_high_wmark)) scan_balance = SCAN_ANON; - goto out; - } } /* - * If there is enough inactive page cache, i.e. if the size of the - * inactive list is greater than that of the active list *and* the - * inactive list actually has some pages to scan on this priority, we - * do not reclaim anything from the anonymous working set right now. - * Without the second condition we could end up never scanning an - * lruvec even if it has plenty of old anonymous pages unless the - * system is under heavy pressure. + * Make sure there are enough pages on the biased LRU before we go + * and do an exclusive reclaim from that list, i.e. if the + * size of the inactive list is greater than that of the active list + * *and* the inactive list actually has some pages to scan on this + * priority. + * Without the second condition we could end up never scanning other + * lruvecs even if they have plenty of old pages unless the system is + * under heavy pressure. */ - if (!inactive_list_is_low(lruvec, true, memcg, sc, false) && - lruvec_lru_size(lruvec, LRU_INACTIVE_FILE, sc->reclaim_idx) >> sc->priority) { - scan_balance = SCAN_FILE; + lru = LRU_INACTIVE_ANON + LRU_FILE * (scan_balance == SCAN_FILE);
This part seems to complicate the logic since it determines the lru under test based on the current setting of scan_balance. I think I prefer individual heuristics with well written comments, but others may feel differently about this.
+ if (!inactive_list_is_low(lruvec, is_file_lru(lru), memcg, sc, false) && + lruvec_lru_size(lruvec, lru, sc->reclaim_idx) >> sc->priority) goto out; - } scan_balance = SCAN_FRACT;
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