Re: [PATCH 2/2] mm/vmscan: calculate reclaimed slab caches in all reclaim paths

[Kirill Tkhai <ktkhai@virtuozzo.com>]

On 21.06.2019 13:14, Yafang Shao wrote:
> There're six different reclaim paths by now,
> - kswapd reclaim path
> - node reclaim path
> - hibernate preallocate memory reclaim path
> - direct reclaim path
> - memcg reclaim path
> - memcg softlimit reclaim path
> 
> The slab caches reclaimed in these paths are only calculated in the above
> three paths.
> 
> There're some drawbacks if we don't calculate the reclaimed slab caches.
> - The sc->nr_reclaimed isn't correct if there're some slab caches
>   relcaimed in this path.
> - The slab caches may be reclaimed thoroughly if there're lots of
>   reclaimable slab caches and few page caches.
>   Let's take an easy example for this case.
>   If one memcg is full of slab caches and the limit of it is 512M, in
>   other words there're approximately 512M slab caches in this memcg.
>   Then the limit of the memcg is reached and the memcg reclaim begins,
>   and then in this memcg reclaim path it will continuesly reclaim the
>   slab caches until the sc->priority drops to 0.
>   After this reclaim stops, you will find there're few slab caches left,
>   which is less than 20M in my test case.
>   While after this patch applied the number is greater than 300M and
>   the sc->priority only drops to 3.
> 
> Signed-off-by: Yafang Shao <laoar.shao@gmail.com>
> ---
>  mm/vmscan.c | 7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index 18a66e5..d6c3fc8 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -3164,11 +3164,13 @@ unsigned long try_to_free_pages(struct zonelist *zonelist, int order,
>  	if (throttle_direct_reclaim(sc.gfp_mask, zonelist, nodemask))
>  		return 1;
>  
> +	current->reclaim_state = &sc.reclaim_state;
>  	trace_mm_vmscan_direct_reclaim_begin(order, sc.gfp_mask);
>  
>  	nr_reclaimed = do_try_to_free_pages(zonelist, &sc);
>  
>  	trace_mm_vmscan_direct_reclaim_end(nr_reclaimed);
> +	current->reclaim_state = NULL;

Shouldn't we remove reclaim_state assignment from __perform_reclaim() after this?
  
>  	return nr_reclaimed;
>  }
> @@ -3191,6 +3193,7 @@ unsigned long mem_cgroup_shrink_node(struct mem_cgroup *memcg,
>  	};
>  	unsigned long lru_pages;
>  
> +	current->reclaim_state = &sc.reclaim_state;
>  	sc.gfp_mask = (gfp_mask & GFP_RECLAIM_MASK) |
>  			(GFP_HIGHUSER_MOVABLE & ~GFP_RECLAIM_MASK);
>  
> @@ -3212,7 +3215,9 @@ unsigned long mem_cgroup_shrink_node(struct mem_cgroup *memcg,
>  					cgroup_ino(memcg->css.cgroup),
>  					sc.nr_reclaimed);
>  
> +	current->reclaim_state = NULL;
>  	*nr_scanned = sc.nr_scanned;
> +
>  	return sc.nr_reclaimed;
>  }
>  
> @@ -3239,6 +3244,7 @@ unsigned long try_to_free_mem_cgroup_pages(struct mem_cgroup *memcg,
>  		.may_shrinkslab = 1,
>  	};
>  
> +	current->reclaim_state = &sc.reclaim_state;
>  	/*
>  	 * Unlike direct reclaim via alloc_pages(), memcg's reclaim doesn't
>  	 * take care of from where we get pages. So the node where we start the
> @@ -3263,6 +3269,7 @@ unsigned long try_to_free_mem_cgroup_pages(struct mem_cgroup *memcg,
>  	trace_mm_vmscan_memcg_reclaim_end(
>  				cgroup_ino(memcg->css.cgroup),
>  				nr_reclaimed);
> +	current->reclaim_state = NULL;
>  
>  	return nr_reclaimed;
>  }
>