On Fri, Jun 25, 2021 at 12:33 AM Huang Ying <ying.huang@xxxxxxxxx> wrote:
>
> From: Keith Busch <kbusch@xxxxxxxxxx>
>
> Reclaim anonymous pages if a migration path is available now that
> demotion provides a non-swap recourse for reclaiming anon pages.
>
> Note that this check is subtly different from the
> anon_should_be_aged() checks. This mechanism checks whether a
> specific page in a specific context *can* actually be reclaimed, given
> current swap space and cgroup limits
>
> anon_should_be_aged() is a much simpler and more preliminary check
> which just says whether there is a possibility of future reclaim.
>
> Cc: Keith Busch <kbusch@xxxxxxxxxx>
> Signed-off-by: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
> Signed-off-by: "Huang, Ying" <ying.huang@xxxxxxxxx>
> Reviewed-by: Yang Shi <shy828301@xxxxxxxxx>
> Cc: Michal Hocko <mhocko@xxxxxxxx>
> Cc: Zi Yan <ziy@xxxxxxxxxx>
> Cc: Wei Xu <weixugc@xxxxxxxxxx>
> Cc: David Rientjes <rientjes@xxxxxxxxxx>
> Cc: Dan Williams <dan.j.williams@xxxxxxxxx>
> Cc: David Hildenbrand <david@xxxxxxxxxx>
>
> --
>
> Changes since 20210618:
> * Consider whether demotion is disabled
>
> Changes from Dave 202010:
> * remove 'total_swap_pages' modification
>
> Changes from Dave 202006:
> * rename reclaim_anon_pages()->can_reclaim_anon_pages()
>
> Note: Keith's Intel SoB is commented out because he is no
> longer at Intel and his @intel.com mail will bounce.
> ---
> mm/vmscan.c | 37 ++++++++++++++++++++++++++++++++++---
> 1 file changed, 34 insertions(+), 3 deletions(-)
>
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index 55f6192b2a51..fce43c7970d7 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -519,6 +519,36 @@ static long add_nr_deferred(long nr, struct shrinker *shrinker,
> return atomic_long_add_return(nr, &shrinker->nr_deferred[nid]);
> }
>
> +static inline bool can_reclaim_anon_pages(struct mem_cgroup *memcg,
> + int node_id,
> + struct scan_control *sc)
> +{
> + if (memcg == NULL) {
> + /*
> + * For non-memcg reclaim, is there
> + * space in any swap device?
> + */
> + if (get_nr_swap_pages() > 0)
> + return true;
> + } else {
> + /* Is the memcg below its swap limit? */
> + if (mem_cgroup_get_nr_swap_pages(memcg) > 0)
> + return true;
> + }
> +
> + /*
> + * The page can not be swapped.
> + *
> + * Can it be reclaimed from this node via demotion?
> + */
> + if ((!sc || !sc->no_demotion) &&
> + next_demotion_node(node_id) != NUMA_NO_NODE)
> + return true;
It is better to abstract these checks into a function, e.g.
can_demote_anon_pages(), to share with anon_can_be_aged().
> + /* No way to reclaim anon pages */
> + return false;
> +}
> +
> /*
> * This misses isolated pages which are not accounted for to save counters.
> * As the data only determines if reclaim or compaction continues, it is
> @@ -530,7 +560,7 @@ unsigned long zone_reclaimable_pages(struct zone *zone)
>
> nr = zone_page_state_snapshot(zone, NR_ZONE_INACTIVE_FILE) +
> zone_page_state_snapshot(zone, NR_ZONE_ACTIVE_FILE);
> - if (get_nr_swap_pages() > 0)
> + if (can_reclaim_anon_pages(NULL, zone_to_nid(zone), NULL))
> nr += zone_page_state_snapshot(zone, NR_ZONE_INACTIVE_ANON) +
> zone_page_state_snapshot(zone, NR_ZONE_ACTIVE_ANON);
>
> @@ -2531,6 +2561,7 @@ enum scan_balance {
> static void get_scan_count(struct lruvec *lruvec, struct scan_control *sc,
> unsigned long *nr)
> {
> + struct pglist_data *pgdat = lruvec_pgdat(lruvec);
> struct mem_cgroup *memcg = lruvec_memcg(lruvec);
> unsigned long anon_cost, file_cost, total_cost;
> int swappiness = mem_cgroup_swappiness(memcg);
> @@ -2541,7 +2572,7 @@ static void get_scan_count(struct lruvec *lruvec, struct scan_control *sc,
> 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) {
> + if (!sc->may_swap || !can_reclaim_anon_pages(memcg, pgdat->node_id, sc)) {
> scan_balance = SCAN_FILE;
> goto out;
> }
> @@ -2916,7 +2947,7 @@ static inline bool should_continue_reclaim(struct pglist_data *pgdat,
> */
> pages_for_compaction = compact_gap(sc->order);
> inactive_lru_pages = node_page_state(pgdat, NR_INACTIVE_FILE);
> - if (get_nr_swap_pages() > 0)
> + if (can_reclaim_anon_pages(NULL, pgdat->node_id, sc))
> inactive_lru_pages += node_page_state(pgdat, NR_INACTIVE_ANON);
>
> return inactive_lru_pages > pages_for_compaction;
> --
> 2.30.2
>
