On Wed, 3 May 2017, Michal Hocko wrote:
> 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.
> @@ -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.
> @@ -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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