linux-kernel - Re: [PATCH] mm/vmscan: DRY cleanup for do_try_to_free

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Date:   Fri, 18 Dec 2020 11:51:53 +0100
From:   Michal Hocko <mhocko@...e.com>
To:     Jacob Wen <jian.w.wen@...cle.com>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        akpm@...ux-foundation.org
Subject: Re: [PATCH] mm/vmscan: DRY cleanup for do_try_to_free_pages()

On Fri 18-12-20 18:22:17, Jacob Wen wrote:
> This patch reduces repetition of set_task_reclaim_state() around
> do_try_to_free_pages().

The changelog really should be talking about why this is needed/useful.
>From the above it is not really clear whether you aimed at doing
a clean up or this is a fix for some misbehavior. I do assume the former
but this should be clearly articulated.

> Signed-off-by: Jacob Wen <jian.w.wen@...cle.com>
> ---
>  mm/vmscan.c | 27 ++++++++++++++++-----------
>  1 file changed, 16 insertions(+), 11 deletions(-)
> 
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index 257cba79a96d..4bc244b23686 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -3023,6 +3023,10 @@ static unsigned long do_try_to_free_pages(struct zonelist *zonelist,
>  	pg_data_t *last_pgdat;
>  	struct zoneref *z;
>  	struct zone *zone;
> +	unsigned long ret;
> +
> +	set_task_reclaim_state(current, &sc->reclaim_state);
> +
>  retry:
>  	delayacct_freepages_start();
>  
> @@ -3069,12 +3073,16 @@ static unsigned long do_try_to_free_pages(struct zonelist *zonelist,
>  
>  	delayacct_freepages_end();
>  
> -	if (sc->nr_reclaimed)
> -		return sc->nr_reclaimed;
> +	if (sc->nr_reclaimed) {
> +		ret = sc->nr_reclaimed;
> +		goto out;
> +	}
>  
>  	/* Aborted reclaim to try compaction? don't OOM, then */
> -	if (sc->compaction_ready)
> -		return 1;
> +	if (sc->compaction_ready) {
> +		ret = 1;
> +		goto out;
> +	}
>  
>  	/*
>  	 * We make inactive:active ratio decisions based on the node's
> @@ -3101,7 +3109,10 @@ static unsigned long do_try_to_free_pages(struct zonelist *zonelist,
>  		goto retry;
>  	}
>  
> -	return 0;
> +	ret = 0;
> +out:
> +	set_task_reclaim_state(current, NULL);
> +	return ret;
>  }
>  
>  static bool allow_direct_reclaim(pg_data_t *pgdat)
> @@ -3269,13 +3280,11 @@ unsigned long try_to_free_pages(struct zonelist *zonelist, int order,
>  	if (throttle_direct_reclaim(sc.gfp_mask, zonelist, nodemask))
>  		return 1;
>  
> -	set_task_reclaim_state(current, &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);
> -	set_task_reclaim_state(current, NULL);
>  
>  	return nr_reclaimed;
>  }
> @@ -3347,7 +3356,6 @@ unsigned long try_to_free_mem_cgroup_pages(struct mem_cgroup *memcg,
>  	 */
>  	struct zonelist *zonelist = node_zonelist(numa_node_id(), sc.gfp_mask);
>  
> -	set_task_reclaim_state(current, &sc.reclaim_state);
>  	trace_mm_vmscan_memcg_reclaim_begin(0, sc.gfp_mask);
>  	noreclaim_flag = memalloc_noreclaim_save();
>  
> @@ -3355,7 +3363,6 @@ unsigned long try_to_free_mem_cgroup_pages(struct mem_cgroup *memcg,
>  
>  	memalloc_noreclaim_restore(noreclaim_flag);
>  	trace_mm_vmscan_memcg_reclaim_end(nr_reclaimed);
> -	set_task_reclaim_state(current, NULL);
>  
>  	return nr_reclaimed;
>  }
> @@ -4023,11 +4030,9 @@ unsigned long shrink_all_memory(unsigned long nr_to_reclaim)
>  
>  	fs_reclaim_acquire(sc.gfp_mask);
>  	noreclaim_flag = memalloc_noreclaim_save();
> -	set_task_reclaim_state(current, &sc.reclaim_state);
>  
>  	nr_reclaimed = do_try_to_free_pages(zonelist, &sc);
>  
> -	set_task_reclaim_state(current, NULL);
>  	memalloc_noreclaim_restore(noreclaim_flag);
>  	fs_reclaim_release(sc.gfp_mask);
>  
> -- 
> 2.25.1
> 

-- 
Michal Hocko
SUSE Labs