Re: [PATCH RFC 05/15] mm/mglru: move max_seq read into walk_update_folio

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

On 08/04/26 at 03:47am, Kairui Song via B4 Relay wrote:
> From: Kairui Song <kasong@tencent.com>
> 
> walk_pte_range(), walk_pmd_range_locked(), and lru_gen_look_around()
> each read lrugen->max_seq to compute the target generation for
> folio_update_gen(), then pass it as a parameter to
> walk_update_folio().  Move the read into walk_update_folio() itself
> so the callers no longer need to compute or pass the value.
> 
> This is a pure refactoring: no functional change.
> 
> Signed-off-by: Kairui Song <kasong@tencent.com>
> ---
>  mm/vmscan.c | 29 ++++++++++++-----------------
>  1 file changed, 12 insertions(+), 17 deletions(-)

Nice clean up.

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

> 
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index b02d2ec8ff4b..c2ea92c2b69e 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -3511,13 +3511,15 @@ static bool suitable_to_scan(int total, int young)
>  }
>  
>  static void walk_update_folio(struct lru_gen_mm_walk *walk, struct vm_area_struct *vma,
> -		struct folio *folio, int new_gen, bool dirty)
> +			      struct lruvec *lruvec, struct folio *folio, bool dirty)
>  {
> -	int old_gen;
> +	int new_gen, old_gen;
>  
>  	if (!folio)
>  		return;
>  
> +	new_gen = lru_gen_from_seq(READ_ONCE(lruvec->lrugen.max_seq));
> +
>  	if (dirty && !folio_test_dirty(folio) &&
>  	    !(folio_test_anon(folio) && folio_test_swapbacked(folio) &&
>  	      !folio_test_swapcache(folio)))
> @@ -3548,8 +3550,6 @@ static bool walk_pte_range(pmd_t *pmd, unsigned long start, unsigned long end,
>  	struct lru_gen_mm_walk *walk = args->private;
>  	struct mem_cgroup *memcg = lruvec_memcg(walk->lruvec);
>  	struct pglist_data *pgdat = lruvec_pgdat(walk->lruvec);
> -	DEFINE_MAX_SEQ(walk->lruvec);
> -	int gen = lru_gen_from_seq(max_seq);
>  	unsigned int nr;
>  	pmd_t pmdval;
>  
> @@ -3600,7 +3600,7 @@ static bool walk_pte_range(pmd_t *pmd, unsigned long start, unsigned long end,
>  			continue;
>  
>  		if (last != folio) {
> -			walk_update_folio(walk, args->vma, last, gen, dirty);
> +			walk_update_folio(walk, args->vma, walk->lruvec, last, dirty);
>  
>  			last = folio;
>  			dirty = false;
> @@ -3613,7 +3613,7 @@ static bool walk_pte_range(pmd_t *pmd, unsigned long start, unsigned long end,
>  		walk->mm_stats[MM_LEAF_YOUNG] += nr;
>  	}
>  
> -	walk_update_folio(walk, args->vma, last, gen, dirty);
> +	walk_update_folio(walk, args->vma, walk->lruvec, last, dirty);
>  	last = NULL;
>  
>  	if (i < PTRS_PER_PTE && get_next_vma(PMD_MASK, PAGE_SIZE, args, &start, &end))
> @@ -3636,8 +3636,6 @@ static void walk_pmd_range_locked(pud_t *pud, unsigned long addr, struct vm_area
>  	struct lru_gen_mm_walk *walk = args->private;
>  	struct mem_cgroup *memcg = lruvec_memcg(walk->lruvec);
>  	struct pglist_data *pgdat = lruvec_pgdat(walk->lruvec);
> -	DEFINE_MAX_SEQ(walk->lruvec);
> -	int gen = lru_gen_from_seq(max_seq);
>  
>  	VM_WARN_ON_ONCE(pud_leaf(*pud));
>  
> @@ -3691,7 +3689,7 @@ static void walk_pmd_range_locked(pud_t *pud, unsigned long addr, struct vm_area
>  			goto next;
>  
>  		if (last != folio) {
> -			walk_update_folio(walk, vma, last, gen, dirty);
> +			walk_update_folio(walk, vma, walk->lruvec, last, dirty);
>  
>  			last = folio;
>  			dirty = false;
> @@ -3705,7 +3703,7 @@ static void walk_pmd_range_locked(pud_t *pud, unsigned long addr, struct vm_area
>  		i = i > MIN_LRU_BATCH ? 0 : find_next_bit(bitmap, MIN_LRU_BATCH, i) + 1;
>  	} while (i <= MIN_LRU_BATCH);
>  
> -	walk_update_folio(walk, vma, last, gen, dirty);
> +	walk_update_folio(walk, vma, walk->lruvec, last, dirty);
>  
>  	lazy_mmu_mode_disable();
>  	spin_unlock(ptl);
> @@ -4270,8 +4268,6 @@ bool lru_gen_look_around(struct page_vma_mapped_walk *pvmw, unsigned int nr)
>  	struct pglist_data *pgdat = folio_pgdat(folio);
>  	struct lruvec *lruvec;
>  	struct lru_gen_mm_state *mm_state;
> -	unsigned long max_seq;
> -	int gen;
>  
>  	lockdep_assert_held(pvmw->ptl);
>  	VM_WARN_ON_ONCE_FOLIO(folio_test_lru(folio), folio);
> @@ -4308,8 +4304,6 @@ bool lru_gen_look_around(struct page_vma_mapped_walk *pvmw, unsigned int nr)
>  
>  	memcg = get_mem_cgroup_from_folio(folio);
>  	lruvec = mem_cgroup_lruvec(memcg, pgdat);
> -	max_seq = READ_ONCE((lruvec)->lrugen.max_seq);
> -	gen = lru_gen_from_seq(max_seq);
>  	mm_state = get_mm_state(lruvec);
>  
>  	lazy_mmu_mode_enable();
> @@ -4341,7 +4335,7 @@ bool lru_gen_look_around(struct page_vma_mapped_walk *pvmw, unsigned int nr)
>  			continue;
>  
>  		if (last != folio) {
> -			walk_update_folio(walk, vma, last, gen, dirty);
> +			walk_update_folio(walk, vma, lruvec, last, dirty);
>  
>  			last = folio;
>  			dirty = false;
> @@ -4353,13 +4347,14 @@ bool lru_gen_look_around(struct page_vma_mapped_walk *pvmw, unsigned int nr)
>  		young += nr;
>  	}
>  
> -	walk_update_folio(walk, vma, last, gen, dirty);
> +	walk_update_folio(walk, vma, lruvec, last, dirty);
>  
>  	lazy_mmu_mode_disable();
>  
>  	/* feedback from rmap walkers to page table walkers */
>  	if (mm_state && suitable_to_scan(i, young))
> -		update_bloom_filter(mm_state, max_seq, pvmw->pmd);
> +		update_bloom_filter(mm_state, READ_ONCE(lruvec->lrugen.max_seq),
> +				    pvmw->pmd);
>  
>  	mem_cgroup_put(memcg);
>  
> 
> -- 
> 2.55.0
> 
>