Re: [PATCH] mm/compaction: clear total_{migrate,free}_scanned before scanning a new zone

[Andrew Morton <akpm@linux-foundation.org>]

On Mon, 22 Jul 2019 05:54:35 -0400 Yafang Shao <laoar.shao@gmail.com> wrote:

> total_{migrate,free}_scanned will be added to COMPACTMIGRATE_SCANNED and
> COMPACTFREE_SCANNED in compact_zone(). We should clear them before scanning
> a new zone.
> In the proc triggered compaction, we forgot clearing them.

It isn't the worst bug we've ever had, but I'm thinking we should
backport the fix into -stable kernels?

> --- a/mm/compaction.c
> +++ b/mm/compaction.c
> @@ -2405,8 +2405,6 @@ static void compact_node(int nid)
>  	struct zone *zone;
>  	struct compact_control cc = {
>  		.order = -1,
> -		.total_migrate_scanned = 0,
> -		.total_free_scanned = 0,
>  		.mode = MIGRATE_SYNC,
>  		.ignore_skip_hint = true,
>  		.whole_zone = true,
> @@ -2422,6 +2420,8 @@ static void compact_node(int nid)
>  
>  		cc.nr_freepages = 0;
>  		cc.nr_migratepages = 0;
> +		cc.total_migrate_scanned = 0;
> +		cc.total_free_scanned = 0;
>  		cc.zone = zone;
>  		INIT_LIST_HEAD(&cc.freepages);
>  		INIT_LIST_HEAD(&cc.migratepages);