Re: [PATCH] mm, memcg: do full scan initially in force_empty

[Michal Hocko <mhocko@suse.com>]

On Tue 28-07-20 03:40:32, Yafang Shao wrote:
> Sometimes we use memory.force_empty to drop pages in a memcg to work
> around some memory pressure issues. When we use force_empty, we want the
> pages can be reclaimed ASAP, however force_empty reclaims pages as a
> regular reclaimer which scans the page cache LRUs from DEF_PRIORITY
> priority and finally it will drop to 0 to do full scan. That is a waste
> of time, we'd better do full scan initially in force_empty.

Do you have any numbers please?

> Signed-off-by: Yafang Shao <laoar.shao@gmail.com>
> ---
>  include/linux/swap.h |  3 ++-
>  mm/memcontrol.c      | 16 ++++++++++------
>  mm/vmscan.c          |  5 +++--
>  3 files changed, 15 insertions(+), 9 deletions(-)
> 
> diff --git a/include/linux/swap.h b/include/linux/swap.h
> index 5b3216ba39a9..d88430f1b964 100644
> --- a/include/linux/swap.h
> +++ b/include/linux/swap.h
> @@ -364,7 +364,8 @@ extern int __isolate_lru_page(struct page *page, isolate_mode_t mode);
>  extern unsigned long try_to_free_mem_cgroup_pages(struct mem_cgroup *memcg,
>  						  unsigned long nr_pages,
>  						  gfp_t gfp_mask,
> -						  bool may_swap);
> +						  bool may_swap,
> +						  int priority);
>  extern unsigned long mem_cgroup_shrink_node(struct mem_cgroup *mem,
>  						gfp_t gfp_mask, bool noswap,
>  						pg_data_t *pgdat,
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index 13f559af1ab6..c873a98f8c7e 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -2237,7 +2237,8 @@ static void reclaim_high(struct mem_cgroup *memcg,
>  		    READ_ONCE(memcg->memory.high))
>  			continue;
>  		memcg_memory_event(memcg, MEMCG_HIGH);
> -		try_to_free_mem_cgroup_pages(memcg, nr_pages, gfp_mask, true);
> +		try_to_free_mem_cgroup_pages(memcg, nr_pages, gfp_mask, true,
> +					     DEF_PRIORITY);
>  	} while ((memcg = parent_mem_cgroup(memcg)) &&
>  		 !mem_cgroup_is_root(memcg));
>  }
> @@ -2515,7 +2516,8 @@ static int try_charge(struct mem_cgroup *memcg, gfp_t gfp_mask,
>  	memcg_memory_event(mem_over_limit, MEMCG_MAX);
>  
>  	nr_reclaimed = try_to_free_mem_cgroup_pages(mem_over_limit, nr_pages,
> -						    gfp_mask, may_swap);
> +						    gfp_mask, may_swap,
> +						    DEF_PRIORITY);
>  
>  	if (mem_cgroup_margin(mem_over_limit) >= nr_pages)
>  		goto retry;
> @@ -3089,7 +3091,8 @@ static int mem_cgroup_resize_max(struct mem_cgroup *memcg,
>  		}
>  
>  		if (!try_to_free_mem_cgroup_pages(memcg, 1,
> -					GFP_KERNEL, !memsw)) {
> +					GFP_KERNEL, !memsw,
> +					DEF_PRIORITY)) {
>  			ret = -EBUSY;
>  			break;
>  		}
> @@ -3222,7 +3225,8 @@ static int mem_cgroup_force_empty(struct mem_cgroup *memcg)
>  			return -EINTR;
>  
>  		progress = try_to_free_mem_cgroup_pages(memcg, 1,
> -							GFP_KERNEL, true);
> +							GFP_KERNEL, true,
> +							0);
>  		if (!progress) {
>  			nr_retries--;
>  			/* maybe some writeback is necessary */
> @@ -6065,7 +6069,7 @@ static ssize_t memory_high_write(struct kernfs_open_file *of,
>  		}
>  
>  		reclaimed = try_to_free_mem_cgroup_pages(memcg, nr_pages - high,
> -							 GFP_KERNEL, true);
> +							 GFP_KERNEL, true, DEF_PRIORITY);
>  
>  		if (!reclaimed && !nr_retries--)
>  			break;
> @@ -6113,7 +6117,7 @@ static ssize_t memory_max_write(struct kernfs_open_file *of,
>  
>  		if (nr_reclaims) {
>  			if (!try_to_free_mem_cgroup_pages(memcg, nr_pages - max,
> -							  GFP_KERNEL, true))
> +							  GFP_KERNEL, true, DEF_PRIORITY))
>  				nr_reclaims--;
>  			continue;
>  		}
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index 749d239c62b2..49298bb2892d 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -3315,7 +3315,8 @@ unsigned long mem_cgroup_shrink_node(struct mem_cgroup *memcg,
>  unsigned long try_to_free_mem_cgroup_pages(struct mem_cgroup *memcg,
>  					   unsigned long nr_pages,
>  					   gfp_t gfp_mask,
> -					   bool may_swap)
> +					   bool may_swap,
> +					   int priority)
>  {
>  	unsigned long nr_reclaimed;
>  	unsigned long pflags;
> @@ -3326,7 +3327,7 @@ unsigned long try_to_free_mem_cgroup_pages(struct mem_cgroup *memcg,
>  				(GFP_HIGHUSER_MOVABLE & ~GFP_RECLAIM_MASK),
>  		.reclaim_idx = MAX_NR_ZONES - 1,
>  		.target_mem_cgroup = memcg,
> -		.priority = DEF_PRIORITY,
> +		.priority = priority,
>  		.may_writepage = !laptop_mode,
>  		.may_unmap = 1,
>  		.may_swap = may_swap,
> -- 
> 2.18.1

-- 
Michal Hocko
SUSE Labs