Re: [PATCH] vmscan: evict use-once pages first (v3)

[Andrew Morton]

On Wed, 29 Apr 2009 13:14:36 -0400
Rik van Riel <riel@xxxxxxxxxx> wrote:

> When the file LRU lists are dominated by streaming IO pages,
> evict those pages first, before considering evicting other
> pages.
> 
> This should be safe from deadlocks or performance problems
> because only three things can happen to an inactive file page:
> 1) referenced twice and promoted to the active list
> 2) evicted by the pageout code
> 3) under IO, after which it will get evicted or promoted
> 
> The pages freed in this way can either be reused for streaming
> IO, or allocated for something else. If the pages are used for
> streaming IO, this pageout pattern continues. Otherwise, we will
> fall back to the normal pageout pattern.
> 
> ..
>
> +int mem_cgroup_inactive_file_is_low(struct mem_cgroup *memcg)
> +{
> +	unsigned long active;
> +	unsigned long inactive;
> +
> +	inactive = mem_cgroup_get_local_zonestat(memcg, LRU_INACTIVE_FILE);
> +	active = mem_cgroup_get_local_zonestat(memcg, LRU_ACTIVE_FILE);
> +
> +	return (active > inactive);
> +}

This function could trivially be made significantly more efficient by
changing it to do a single pass over all the zones of all the nodes,
rather than two passes.

>  static unsigned long shrink_list(enum lru_list lru, unsigned long nr_to_scan,
>  	struct zone *zone, struct scan_control *sc, int priority)
>  {
>  	int file = is_file_lru(lru);
>  
> -	if (lru == LRU_ACTIVE_FILE) {
> +	if (lru == LRU_ACTIVE_FILE && inactive_file_is_low(zone, sc)) {
>  		shrink_active_list(nr_to_scan, zone, sc, priority, file);
>  		return 0;
>  	}

And it does get called rather often.
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