Re: [PATCH v6 6/7] mm/mglru: add lruvec_gen_size() helper

[Baoquan He <baoquan.he@linux.dev>]

On 11/03/26 at 10:56am, Ridong Chen wrote:
> From: Ridong Chen <chenridong@xiaomi.com>
> 
> The number of pages of a given type in a generation is computed by
> summing lrugen->nr_pages[gen][type][] over all zones and clamping each
> per-zone counter to >= 0, since the counters are updated locklessly and
> can transiently go negative. This loop is open-coded in
> lruvec_evictable_size() and in the debugfs lru_gen output.
> 
> Add lruvec_gen_size() to compute it from a seq, and convert both users.
> Put it in mm/vmscan.h so that the vmscan tracepoints, which include that
> header, can use it as well.
> An upcoming tracepoint and the MGLRU swappiness rework will also use it.
> 
> No functional change.
> 
> Suggested-by: Barry Song <baohua@kernel.org>
> Signed-off-by: Ridong Chen <chenridong@xiaomi.com>
> ---
>  mm/vmscan.c | 18 ++++++------------
>  mm/vmscan.h | 16 ++++++++++++++++
>  2 files changed, 22 insertions(+), 12 deletions(-)

LGTM,

Reviewed-by: Baoquan He <baoquan.he@linux.dev>

> 
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index 3054175717ab..1581b73aec56 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -4207,18 +4207,15 @@ static void set_initial_priority(struct pglist_data *pgdat, struct scan_control
>  
>  static unsigned long lruvec_evictable_size(struct lruvec *lruvec, int swappiness)
>  {
> -	int gen, type, zone;
> +	int type;
>  	unsigned long seq, total = 0;
>  	struct lru_gen_folio *lrugen = &lruvec->lrugen;
>  	DEFINE_MAX_SEQ(lruvec);
>  	DEFINE_MIN_SEQ(lruvec);
>  
>  	for_each_evictable_type(type, swappiness) {
> -		for (seq = min_seq[type]; seq <= max_seq; seq++) {
> -			gen = lru_gen_from_seq(seq);
> -			for (zone = 0; zone < MAX_NR_ZONES; zone++)
> -				total += max(READ_ONCE(lrugen->nr_pages[gen][type][zone]), 0L);
> -		}
> +		for (seq = min_seq[type]; seq <= max_seq; seq++)
> +			total += lruvec_gen_size(lrugen, type, seq);
>  	}
>  
>  	return total;
> @@ -5723,20 +5720,17 @@ static int lru_gen_seq_show(struct seq_file *m, void *v)
>  		seq = 0;
>  
>  	for (; seq <= max_seq; seq++) {
> -		int type, zone;
> +		int type;
>  		int gen = lru_gen_from_seq(seq);
>  		unsigned long birth = READ_ONCE(lruvec->lrugen.timestamps[gen]);
>  
>  		seq_printf(m, " %10lu %10u", seq, jiffies_to_msecs(jiffies - birth));
>  
>  		for (type = 0; type < ANON_AND_FILE; type++) {
> -			unsigned long size = 0;
>  			char mark = full && seq < min_seq[type] ? 'x' : ' ';
>  
> -			for (zone = 0; zone < MAX_NR_ZONES; zone++)
> -				size += max(READ_ONCE(lrugen->nr_pages[gen][type][zone]), 0L);
> -
> -			seq_printf(m, " %10lu%c", size, mark);
> +			seq_printf(m, " %10lu%c",
> +				   lruvec_gen_size(lrugen, type, seq), mark);
>  		}
>  
>  		seq_putc(m, '\n');
> diff --git a/mm/vmscan.h b/mm/vmscan.h
> index adb22e80d760..c6b583fc7493 100644
> --- a/mm/vmscan.h
> +++ b/mm/vmscan.h
> @@ -3,6 +3,7 @@
>  #define _MM_VMSCAN_H
>  
>  #include <linux/gfp_types.h>
> +#include <linux/mm_inline.h>
>  #include <linux/nodemask.h>
>  #include <linux/swap.h>
>  #include <linux/types.h>
> @@ -115,4 +116,19 @@ struct scan_control {
>  	struct reclaim_state reclaim_state;
>  };
>  
> +#ifdef CONFIG_LRU_GEN
> +/* The number of pages of @type in the generation @seq, summed over all zones */
> +static inline unsigned long lruvec_gen_size(struct lru_gen_folio *lrugen,
> +					    int type, unsigned long seq)
> +{
> +	int gen = lru_gen_from_seq(seq);
> +	unsigned long size = 0;
> +
> +	for (int zone = 0; zone < MAX_NR_ZONES; zone++)
> +		size += max(READ_ONCE(lrugen->nr_pages[gen][type][zone]), 0L);
> +
> +	return size;
> +}
> +#endif /* CONFIG_LRU_GEN */
> +
>  #endif /* _MM_VMSCAN_H */
> -- 
> 2.34.1
>