On Thu, Mar 4, 2021 at 4:01 PM Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx> wrote:
>
>
> From: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
>
> Anonymous pages are kept on their own LRU(s). These lists could
> theoretically always be scanned and maintained. But, without swap,
> there is currently nothing the kernel can *do* with the results of a
> scanned, sorted LRU for anonymous pages.
>
> A check for '!total_swap_pages' currently serves as a valid check as
> to whether anonymous LRUs should be maintained. However, another
> method will be added shortly: page demotion.
>
> Abstract out the 'total_swap_pages' checks into a helper, give it a
> logically significant name, and check for the possibility of page
> demotion.
Reviewed-by: Yang Shi <shy828301@xxxxxxxxx>
>
> Signed-off-by: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
> Cc: David Rientjes <rientjes@xxxxxxxxxx>
> Cc: Huang Ying <ying.huang@xxxxxxxxx>
> Cc: Dan Williams <dan.j.williams@xxxxxxxxx>
> Cc: David Hildenbrand <david@xxxxxxxxxx>
> Cc: osalvador <osalvador@xxxxxxx>
> ---
>
> b/mm/vmscan.c | 28 +++++++++++++++++++++++++---
> 1 file changed, 25 insertions(+), 3 deletions(-)
>
> diff -puN mm/vmscan.c~mm-vmscan-anon-can-be-aged mm/vmscan.c
> --- a/mm/vmscan.c~mm-vmscan-anon-can-be-aged 2021-03-04 15:35:58.935806422 -0800
> +++ b/mm/vmscan.c 2021-03-04 15:35:58.942806422 -0800
> @@ -2517,6 +2517,26 @@ out:
> }
> }
>
> +/*
> + * Anonymous LRU management is a waste if there is
> + * ultimately no way to reclaim the memory.
> + */
> +bool anon_should_be_aged(struct lruvec *lruvec)
> +{
> + struct pglist_data *pgdat = lruvec_pgdat(lruvec);
> +
> + /* Aging the anon LRU is valuable if swap is present: */
> + if (total_swap_pages > 0)
> + return true;
> +
> + /* Also valuable if anon pages can be demoted: */
> + if (next_demotion_node(pgdat->node_id) >= 0)
> + return true;
> +
> + /* No way to reclaim anon pages. Should not age anon LRUs: */
> + return false;
> +}
> +
> static void shrink_lruvec(struct lruvec *lruvec, struct scan_control *sc)
> {
> unsigned long nr[NR_LRU_LISTS];
> @@ -2626,7 +2646,8 @@ static void shrink_lruvec(struct lruvec
> * Even if we did not try to evict anon pages at all, we want to
> * rebalance the anon lru active/inactive ratio.
> */
> - if (total_swap_pages && inactive_is_low(lruvec, LRU_INACTIVE_ANON))
> + if (anon_should_be_aged(lruvec) &&
> + inactive_is_low(lruvec, LRU_INACTIVE_ANON))
> shrink_active_list(SWAP_CLUSTER_MAX, lruvec,
> sc, LRU_ACTIVE_ANON);
> }
> @@ -3455,10 +3476,11 @@ static void age_active_anon(struct pglis
> struct mem_cgroup *memcg;
> struct lruvec *lruvec;
>
> - if (!total_swap_pages)
> + lruvec = mem_cgroup_lruvec(NULL, pgdat);
> +
> + if (!anon_should_be_aged(lruvec))
> return;
>
> - lruvec = mem_cgroup_lruvec(NULL, pgdat);
> if (!inactive_is_low(lruvec, LRU_INACTIVE_ANON))
> return;
>
> _
>
