Re: [PATCH 10/10] mm/migrate: new zone_reclaim_mode to enable reclaim migration

[Wei Xu]

On Thu, Apr 1, 2021 at 11:35 AM Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx> wrote:
> This proposes extending the existing "zone_reclaim_mode" (now
> now really node_reclaim_mode) as a method to enable it.

Nit: now now -> now

> We are open to any alternative that allows end users to enable
> this mechanism or disable it it workload harm is detected (just
> like traditional autonuma).

Nit: it it -> it if

> diff -puN mm/vmscan.c~RECLAIM_MIGRATE mm/vmscan.c
> --- a/mm/vmscan.c~RECLAIM_MIGRATE       2021-03-31 15:17:40.339000190 -0700
> +++ b/mm/vmscan.c       2021-03-31 15:17:40.357000190 -0700
> @@ -1074,6 +1074,9 @@ static bool migrate_demote_page_ok(struc
>         VM_BUG_ON_PAGE(PageHuge(page), page);
>         VM_BUG_ON_PAGE(PageLRU(page), page);
>
> +       if (!(node_reclaim_mode & RECLAIM_MIGRATE))
> +               return false;
> +

As I commented on an earlier patch in this series, the RECLAIM_MIGRATE check
needs to be added to other new callers of next_demotion_node() as well to avoid
unnecessarily splitting THP pages when neither swap nor RECLAIM_MIGRATE
is enabled.  It can be too late to check RECLAIM_MIGRATE only in
migrate_demote_page_ok().