2022-11-22 20:56:12

by Mina Almasry

Subject: [RFC PATCH v1 3/4] mm: Fix demotion-only scanning anon pages

This is likely a missed change from commit a2a36488a61c ("mm/vmscan: Consider
anonymous pages without swap"). Current logic is if !may_swap _or_
!can_reclaim_anon_pages() then we don't scan anon memory.

This should be an 'and'. We would like to scan anon memory if we may swap
or if we can_reclaim_anon_pages().

Fixes: commit a2a36488a61c ("mm/vmscan: Consider anonymous pages without swap")

Signed-off-by: Mina Almasry <[email protected]>
---
mm/vmscan.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 8c1f5416d789..d7e509b3f07f 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -2931,7 +2931,7 @@ 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 folios. */
- if (!sc->may_swap || !can_reclaim_anon_pages(memcg, pgdat->node_id, sc)) {
+ if (!sc->may_swap && !can_reclaim_anon_pages(memcg, pgdat->node_id, sc)) {
scan_balance = SCAN_FILE;
goto out;
}
--
2.38.1.584.g0f3c55d4c2-goog

2022-11-24 05:51:45

by Huang, Ying

Subject: Re: [RFC PATCH v1 3/4] mm: Fix demotion-only scanning anon pages

Mina Almasry <[email protected]> writes:

> This is likely a missed change from commit a2a36488a61c ("mm/vmscan: Consider
> anonymous pages without swap"). Current logic is if !may_swap _or_
> !can_reclaim_anon_pages() then we don't scan anon memory.
>
> This should be an 'and'. We would like to scan anon memory if we may swap
> or if we can_reclaim_anon_pages().
>
> Fixes: commit a2a36488a61c ("mm/vmscan: Consider anonymous pages without swap")
>
> Signed-off-by: Mina Almasry <[email protected]>
> ---
> mm/vmscan.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index 8c1f5416d789..d7e509b3f07f 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -2931,7 +2931,7 @@ 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 folios. */
> - if (!sc->may_swap || !can_reclaim_anon_pages(memcg, pgdat->node_id, sc)) {
> + if (!sc->may_swap && !can_reclaim_anon_pages(memcg, pgdat->node_id, sc)) {

If there is only DRAM but swap device is enabled, sc->may_swap will not
work as expected. So we should check can_demote() instead if
sc->may_swap.

Best Regards,
Huang, Ying

> scan_balance = SCAN_FILE;
> goto out;
> }
> --
> 2.38.1.584.g0f3c55d4c2-goog