Re: [PATCH v2] mm/vmscan: extract calculated pressure balance as a function

[Andrew Morton <akpm@linux-foundation.org>]

On Wed, 15 Jan 2025 09:58:29 +0800 76824143@qq.com wrote:

> From: Hao Zhang <zhanghao1@kylinos.cn>
> 
> Extract pressure balance calculation into a function.This
> doesn't change current behaviour.

OK, I guess it's a slight improvement and the size of my vmscan.o is
unaltered.


> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -2367,6 +2367,43 @@ static void prepare_scan_control(pg_data_t *pgdat, struct scan_control *sc)
>  	}
>  }
>  
> +static inline void calculate_pressure_balance(struct scan_control *sc, int swappiness,
> +			u64 *fraction, u64 *denominator)

As we're wrapping, we may as well wrap within 80 cols:

--- a/mm/vmscan.c~mm-vmscan-extract-calculated-pressure-balance-as-a-function-fix
+++ a/mm/vmscan.c
@@ -2400,8 +2400,8 @@ static void prepare_scan_control(pg_data
 	}
 }
 
-static inline void calculate_pressure_balance(struct scan_control *sc, int swappiness,
-			u64 *fraction, u64 *denominator)
+static inline void calculate_pressure_balance(struct scan_control *sc,
+			int swappiness, u64 *fraction, u64 *denominator)
 {
 	unsigned long anon_cost, file_cost, total_cost;
 	unsigned long ap, fp;
_

_

> +{
> +	unsigned long anon_cost, file_cost, total_cost;
> +	unsigned long ap, fp;
> +
> +	/*
> +	 * Calculate the pressure balance between anon and file pages.
> +	 *
> +	 * The amount of pressure we put on each LRU is inversely
> +	 * proportional to the cost of reclaiming each list, as
> +	 * determined by the share of pages that are refaulting, times
> +	 * the relative IO cost of bringing back a swapped out
> +	 * anonymous page vs reloading a filesystem page (swappiness).
> +	 *
> +	 * Although we limit that influence to ensure no list gets
> +	 * left behind completely: at least a third of the pressure is
> +	 * applied, before swappiness.
> +	 *
> +	 * With swappiness at 100, anon and file have equal IO cost.
> +	 */
> +	total_cost = sc->anon_cost + sc->file_cost;
> +	anon_cost = total_cost + sc->anon_cost;
> +	file_cost = total_cost + sc->file_cost;
> +	total_cost = anon_cost + file_cost;
> +
> +	ap = swappiness * (total_cost + 1);
> +	ap /= anon_cost + 1;
> +
> +	fp = (MAX_SWAPPINESS - swappiness) * (total_cost + 1);
> +	fp /= file_cost + 1;
> +
> +	fraction[WORKINGSET_ANON] = ap;
> +	fraction[WORKINGSET_FILE] = fp;
> +	*denominator = ap + fp;
> +}
> +
>  /*
>   * Determine how aggressively the anon and file LRU lists should be
>   * scanned.
> @@ -2379,12 +2416,10 @@ static void get_scan_count(struct lruvec *lruvec, struct scan_control *sc,
>  {
>  	struct pglist_data *pgdat = lruvec_pgdat(lruvec);
>  	struct mem_cgroup *memcg = lruvec_memcg(lruvec);
> -	unsigned long anon_cost, file_cost, total_cost;
>  	int swappiness = sc_swappiness(sc, memcg);
>  	u64 fraction[ANON_AND_FILE];
>  	u64 denominator = 0;	/* gcc */
>  	enum scan_balance scan_balance;
> -	unsigned long ap, fp;
>  	enum lru_list lru;
>  
>  	/* If we have no swap space, do not bother scanning anon folios. */
> @@ -2433,35 +2468,8 @@ static void get_scan_count(struct lruvec *lruvec, struct scan_control *sc,
>  	}
>  
>  	scan_balance = SCAN_FRACT;
> -	/*
> -	 * Calculate the pressure balance between anon and file pages.
> -	 *
> -	 * The amount of pressure we put on each LRU is inversely
> -	 * proportional to the cost of reclaiming each list, as
> -	 * determined by the share of pages that are refaulting, times
> -	 * the relative IO cost of bringing back a swapped out
> -	 * anonymous page vs reloading a filesystem page (swappiness).
> -	 *
> -	 * Although we limit that influence to ensure no list gets
> -	 * left behind completely: at least a third of the pressure is
> -	 * applied, before swappiness.
> -	 *
> -	 * With swappiness at 100, anon and file have equal IO cost.
> -	 */
> -	total_cost = sc->anon_cost + sc->file_cost;
> -	anon_cost = total_cost + sc->anon_cost;
> -	file_cost = total_cost + sc->file_cost;
> -	total_cost = anon_cost + file_cost;
> -
> -	ap = swappiness * (total_cost + 1);
> -	ap /= anon_cost + 1;
> -
> -	fp = (MAX_SWAPPINESS - swappiness) * (total_cost + 1);
> -	fp /= file_cost + 1;
> +	calculate_pressure_balance(sc, swappiness, fraction, &denominator);
>  
> -	fraction[0] = ap;
> -	fraction[1] = fp;
> -	denominator = ap + fp;
>  out:
>  	for_each_evictable_lru(lru) {
>  		bool file = is_file_lru(lru);
> 
> base-commit: eea6e4b4dfb8859446177c32961c96726d0117be
> -- 
> 2.25.1