Re: [PATCH] mm: bail out when meet the goal of proactive memcg reclaim

[Michal Hocko]

On Wed 21-01-26 17:06:20, zhaoyang.huang wrote:
> From: Zhaoyang Huang <zhaoyang.huang@xxxxxxxxxx>
> 
> The proactive memcg reclaim defines the specific target mem cgroup
> as well as a certain number of memories, which is different to
> the kswapd and direct reclaim that need to keep the fairness among
> cgroups. This commit would like to introduce a criteria to have
> proactive reclaim bail out when target mem cgroup could meet the goal
> via its own lruvec, which means the reclaim would also go through the
> whole tree if the iter start on the desendants.

Could you describe the actual problem you are trying to deal with?
I would be also interested why the limit aplies only to target_memcg.

> 
> Signed-off-by: Zhaoyang Huang <zhaoyang.huang@xxxxxxxxxx>
> ---
>  mm/vmscan.c | 11 +++++++++--
>  1 file changed, 9 insertions(+), 2 deletions(-)
> 
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index 670fe9fae5ba..5dcca4559b18 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -6028,8 +6028,15 @@ static void shrink_node_memcgs(pg_data_t *pgdat, struct scan_control *sc)
>  				   sc->nr_scanned - scanned,
>  				   sc->nr_reclaimed - reclaimed);
>  
> -		/* If partial walks are allowed, bail once goal is reached */
> -		if (partial && sc->nr_reclaimed >= sc->nr_to_reclaim) {
> +		/* If partial walks are allowed, or proactive reclaim where
> +		 * the target memcg is clearly defined that could let us ignore
> +		 * the fairness thing, bail once goal is reached.
> +		 * note: for proactive reclaim, the criteria make sense only
> +		 * when target_memcg has both of descendant groups and folios
> +		 * charged. Other wise, walk the whole tree under target_memcg.
> +		 */
> +		if ((partial || (sc->proactive && target_memcg == memcg)) &&
> +			       sc->nr_reclaimed >= sc->nr_to_reclaim) {
>  			mem_cgroup_iter_break(target_memcg, memcg);
>  			break;
>  		}
> -- 
> 2.25.1

-- 
Michal Hocko
SUSE Labs