Re: [patch 4/4] mm: vmscan: move swappiness out of scan_control

[Michal Hocko <mhocko@suse.cz>]

On Fri 20-06-14 12:33:50, Johannes Weiner wrote:
> Swappiness is determined for each scanned memcg individually in
> shrink_zone() and is not a parameter that applies throughout the
> reclaim scan.  Move it out of struct scan_control to prevent
> accidental use of a stale value.

Yes, putting it into scan_control was a quick&dirty temporal
solution.  I was thinking about something like lruvec_swappiness
(lruvec->mem_cgroup_per_zone->mem_cgroup) and stick it into
get_scan_count but what you have here is better because the swappiness
has memcg scope rather than lruvec.

> Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>

Acked-by: Michal Hocko <mhocko@suse.cz>

> ---
>  mm/vmscan.c | 27 +++++++++++++--------------
>  1 file changed, 13 insertions(+), 14 deletions(-)
> 
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index d0bc1a209746..757e2a8dbf58 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -89,9 +89,6 @@ struct scan_control {
>  	/* Scan (total_size >> priority) pages at once */
>  	int priority;
>  
> -	/* anon vs. file LRUs scanning "ratio" */
> -	int swappiness;
> -
>  	/*
>  	 * The memory cgroup that hit its limit and as a result is the
>  	 * primary target of this reclaim invocation.
> @@ -1868,8 +1865,8 @@ enum scan_balance {
>   * nr[0] = anon inactive pages to scan; nr[1] = anon active pages to scan
>   * nr[2] = file inactive pages to scan; nr[3] = file active pages to scan
>   */
> -static void get_scan_count(struct lruvec *lruvec, struct scan_control *sc,
> -			   unsigned long *nr)
> +static void get_scan_count(struct lruvec *lruvec, int swappiness,
> +			   struct scan_control *sc, unsigned long *nr)
>  {
>  	struct zone_reclaim_stat *reclaim_stat = &lruvec->reclaim_stat;
>  	u64 fraction[2];
> @@ -1912,7 +1909,7 @@ static void get_scan_count(struct lruvec *lruvec, struct scan_control *sc,
>  	 * using the memory controller's swap limit feature would be
>  	 * too expensive.
>  	 */
> -	if (!global_reclaim(sc) && !sc->swappiness) {
> +	if (!global_reclaim(sc) && !swappiness) {
>  		scan_balance = SCAN_FILE;
>  		goto out;
>  	}
> @@ -1922,7 +1919,7 @@ static void get_scan_count(struct lruvec *lruvec, struct scan_control *sc,
>  	 * system is close to OOM, scan both anon and file equally
>  	 * (unless the swappiness setting disagrees with swapping).
>  	 */
> -	if (!sc->priority && sc->swappiness) {
> +	if (!sc->priority && swappiness) {
>  		scan_balance = SCAN_EQUAL;
>  		goto out;
>  	}
> @@ -1965,7 +1962,7 @@ static void get_scan_count(struct lruvec *lruvec, struct scan_control *sc,
>  	 * With swappiness at 100, anonymous and file have the same priority.
>  	 * This scanning priority is essentially the inverse of IO cost.
>  	 */
> -	anon_prio = sc->swappiness;
> +	anon_prio = swappiness;
>  	file_prio = 200 - anon_prio;
>  
>  	/*
> @@ -2055,7 +2052,8 @@ out:
>  /*
>   * This is a basic per-zone page freer.  Used by both kswapd and direct reclaim.
>   */
> -static void shrink_lruvec(struct lruvec *lruvec, struct scan_control *sc)
> +static void shrink_lruvec(struct lruvec *lruvec, int swappiness,
> +			  struct scan_control *sc)
>  {
>  	unsigned long nr[NR_LRU_LISTS];
>  	unsigned long targets[NR_LRU_LISTS];
> @@ -2066,7 +2064,7 @@ static void shrink_lruvec(struct lruvec *lruvec, struct scan_control *sc)
>  	struct blk_plug plug;
>  	bool scan_adjusted;
>  
> -	get_scan_count(lruvec, sc, nr);
> +	get_scan_count(lruvec, swappiness, sc, nr);
>  
>  	/* Record the original scan target for proportional adjustments later */
>  	memcpy(targets, nr, sizeof(nr));
> @@ -2263,11 +2261,12 @@ static unsigned long shrink_zone(struct zone *zone, struct scan_control *sc)
>  		memcg = mem_cgroup_iter(root, NULL, &reclaim);
>  		do {
>  			struct lruvec *lruvec;
> +			int swappiness;
>  
>  			lruvec = mem_cgroup_zone_lruvec(zone, memcg);
> +			swappiness = mem_cgroup_swappiness(memcg);
>  
> -			sc->swappiness = mem_cgroup_swappiness(memcg);
> -			shrink_lruvec(lruvec, sc);
> +			shrink_lruvec(lruvec, swappiness, sc);
>  
>  			/*
>  			 * Direct reclaim and kswapd have to scan all memory
> @@ -2714,10 +2713,10 @@ unsigned long mem_cgroup_shrink_node_zone(struct mem_cgroup *memcg,
>  		.may_swap = !noswap,
>  		.order = 0,
>  		.priority = 0,
> -		.swappiness = mem_cgroup_swappiness(memcg),
>  		.target_mem_cgroup = memcg,
>  	};
>  	struct lruvec *lruvec = mem_cgroup_zone_lruvec(zone, memcg);
> +	int swappiness = mem_cgroup_swappiness(memcg);
>  
>  	sc.gfp_mask = (gfp_mask & GFP_RECLAIM_MASK) |
>  			(GFP_HIGHUSER_MOVABLE & ~GFP_RECLAIM_MASK);
> @@ -2733,7 +2732,7 @@ unsigned long mem_cgroup_shrink_node_zone(struct mem_cgroup *memcg,
>  	 * will pick up pages from other mem cgroup's as well. We hack
>  	 * the priority and make it zero.
>  	 */
> -	shrink_lruvec(lruvec, &sc);
> +	shrink_lruvec(lruvec, swappiness, &sc);
>  
>  	trace_mm_vmscan_memcg_softlimit_reclaim_end(sc.nr_reclaimed);
>  
> -- 
> 2.0.0
> 

-- 
Michal Hocko
SUSE Labs

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