Re: [PATCH mmotm] vmscan: handle may_swap more strictly (Re: [PATCH mmotm] vmscan: fix may_swap handling for memcg)

[KOSAKI Motohiro]

> > > and, too many recliaming pages is not only memcg issue. I don't think this
> > > patch provide generic solution.
> > > 
> > Ah, you're right. It's not only memcg issue.
> > 
> How about this one ?
> 
> ===
> From: Daisuke Nishimura <nishimura@xxxxxxxxxxxxxxxxx>
> 
> Commit 2e2e425989080cc534fc0fca154cae515f971cf5 ("vmscan,memcg: reintroduce
> sc->may_swap) add may_swap flag and handle it at get_scan_ratio().
> 
> But the result of get_scan_ratio() is ignored when priority == 0,
> so anon lru is scanned even if may_swap == 0 or nr_swap_pages == 0.
> IMHO, this is not an expected behavior.
> 
> As for memcg especially, because of this behavior many and many pages are
> swapped-out just in vain when oom is invoked by mem+swap limit.
> 
> This patch is for handling may_swap flag more strictly.
> 
> Signed-off-by: Daisuke Nishimura <nishimura@xxxxxxxxxxxxxxxxx>

Looks great.
your patch doesn't only improve memcg, bug also improve noswap system.

Thanks.
	Reviewed-by: KOSAKI Motohiro <kosaki.motohiro@xxxxxxxxxxxxxx>



> ---
>  mm/vmscan.c |   18 +++++++++---------
>  1 files changed, 9 insertions(+), 9 deletions(-)
> 
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index 2ddcfc8..bacb092 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -1407,13 +1407,6 @@ static void get_scan_ratio(struct zone *zone, struct scan_control *sc,
>  	unsigned long ap, fp;
>  	struct zone_reclaim_stat *reclaim_stat = get_reclaim_stat(zone, sc);
>  
> -	/* If we have no swap space, do not bother scanning anon pages. */
> -	if (!sc->may_swap || (nr_swap_pages <= 0)) {
> -		percent[0] = 0;
> -		percent[1] = 100;
> -		return;
> -	}
> -
>  	anon  = zone_nr_pages(zone, sc, LRU_ACTIVE_ANON) +
>  		zone_nr_pages(zone, sc, LRU_INACTIVE_ANON);
>  	file  = zone_nr_pages(zone, sc, LRU_ACTIVE_FILE) +
> @@ -1511,15 +1504,22 @@ static void shrink_zone(int priority, struct zone *zone,
>  	enum lru_list l;
>  	unsigned long nr_reclaimed = sc->nr_reclaimed;
>  	unsigned long swap_cluster_max = sc->swap_cluster_max;
> +	int noswap = 0;
>  
> -	get_scan_ratio(zone, sc, percent);
> +	/* If we have no swap space, do not bother scanning anon pages. */
> +	if (!sc->may_swap || (nr_swap_pages <= 0)) {
> +		noswap = 1;
> +		percent[0] = 0;
> +		percent[1] = 100;
> +	} else
> +		get_scan_ratio(zone, sc, percent);
>  
>  	for_each_evictable_lru(l) {
>  		int file = is_file_lru(l);
>  		unsigned long scan;
>  
>  		scan = zone_nr_pages(zone, sc, l);
> -		if (priority) {
> +		if (priority || noswap) {
>  			scan >>= priority;
>  			scan = (scan * percent[file]) / 100;
>  		}



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