Re: [PATCH v3 2/2] mm: mglru: promote mapped executable folios after first usage

[Johannes Weiner]

On Fri, Jul 17, 2026 at 06:05:34PM +0800, Baolin Wang wrote:
> Classical LRU protects mapped executable file folios through commit
> 8cab4754d24a0 ("vmscan: make mapped executable pages the first class
> citizen") and commit c909e99364c8 ("vmscan: activate executable pages
> after first usage"), giving executable code a better chance to stay in
> memory, avoiding IO thrashing and improving workload performance.
> 
> However, MGLRU's protection of mapped executable file folios is less
> reliable. Although shrink_folio_list() checks references, the access flag
> of mapped executable file folios may have already been checked and
> cleared by lru_gen_look_around() or walk_mm(). Additionally,
> folio_update_gen() or lru_gen_set_refs() only sets the 'PG_referenced'
> flag for mapped executable file folios, which causes shrink_folio_list()
> to ignore the first usage of these mapped executable file folios and
> reclaim them easily.
> 
> Follow the classical LRU's logic, promoting mapped executable file folios
> after their first usage in folio_update_gen() and lru_gen_set_refs(),
> giving executable code a better chance to stay in memory.
> 
> On my 32-core Arm machine, with the memcg limit set to 2G, running
> 'make -j32' to build kernel showed some improvement in sys time.
> 
> base			patched
> 9248.543s		7861.579s
> 
> While we are at it, introduce a new helper to check mapped executable
> file folios.
> 
> Signed-off-by: Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx>

Both patches contained herein look good:

Acked-by: Johannes Weiner <hannes@xxxxxxxxxxx>
Acked-by: Johannes Weiner <hannes@xxxxxxxxxxx>

[ Sorry ;-) Please don't mix refactoring work with functional
  changes. It's difficult to look through a sequence of diff hunks
  with more than one review narrative interleaved. ]

> ---
>  mm/vmscan.c | 47 +++++++++++++++++++++++++++++++----------------
>  1 file changed, 31 insertions(+), 16 deletions(-)
> 
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index de62899c108d..1040bf9f96e8 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -268,6 +268,12 @@ static int sc_swappiness(struct scan_control *sc, struct mem_cgroup *memcg)
>  }
>  #endif
>  
> +static inline bool is_exec_file_folio(const struct folio *folio,
> +		const vma_flags_t *vma_flags)
> +{
> +	return vma_flags_test(vma_flags, VMA_EXEC_BIT) && folio_is_file_lru(folio);
> +}
> +
>  static void set_task_reclaim_state(struct task_struct *task,
>  				   struct reclaim_state *rs)
>  {
> @@ -835,11 +841,15 @@ enum folio_references {
>   * with PG_active set. In contrast, the aging (page table walk) path uses
>   * folio_update_gen().
>   */
> -static bool lru_gen_set_refs(struct folio *folio)
> +static bool lru_gen_set_refs(struct folio *folio, const vma_flags_t *vma_flags)
>  {
>  	/* see the comment on LRU_REFS_FLAGS */
>  	if (!folio_test_referenced(folio) && !folio_test_workingset(folio)) {
>  		set_mask_bits(&folio->flags.f, LRU_REFS_MASK, BIT(PG_referenced));
> +		/* Activate file-backed executable folios after first usage. */
> +		if (is_exec_file_folio(folio, vma_flags))
> +			return true;
> +
>  		return false;
>  	}
>  
> @@ -851,7 +861,7 @@ static bool lru_gen_set_refs(struct folio *folio)
>  	return true;
>  }
>  #else
> -static bool lru_gen_set_refs(struct folio *folio)
> +static bool lru_gen_set_refs(struct folio *folio, const vma_flags_t *vma_flags)
>  {
>  	return false;
>  }
> @@ -886,7 +896,7 @@ static enum folio_references folio_check_references(struct folio *folio,
>  		if (!referenced_ptes)
>  			return FOLIOREF_RECLAIM;
>  
> -		return lru_gen_set_refs(folio) ? FOLIOREF_ACTIVATE : FOLIOREF_KEEP;
> +		return lru_gen_set_refs(folio, &vma_flags) ? FOLIOREF_ACTIVATE : FOLIOREF_KEEP;
>  	}
>  
>  	referenced_folio = folio_test_clear_referenced(folio);
> @@ -914,7 +924,7 @@ static enum folio_references folio_check_references(struct folio *folio,
>  		/*
>  		 * Activate file-backed executable folios after first usage.
>  		 */
> -		if (vma_flags_test(&vma_flags, VMA_EXEC_BIT) && folio_is_file_lru(folio))
> +		if (is_exec_file_folio(folio, &vma_flags))
>  			return FOLIOREF_ACTIVATE;
>  
>  		return FOLIOREF_KEEP;
> @@ -2119,7 +2129,7 @@ static void shrink_active_list(unsigned long nr_to_scan,
>  			 * IO, plus JVM can create lots of anon VM_EXEC folios,
>  			 * so we ignore them here.
>  			 */
> -			if (vma_flags_test(&vma_flags, VMA_EXEC_BIT) && folio_is_file_lru(folio)) {
> +			if (is_exec_file_folio(folio, &vma_flags)) {
>  				nr_rotated += folio_nr_pages(folio);
>  				list_add(&folio->lru, &l_active);
>  				continue;
> @@ -3188,7 +3198,7 @@ static bool positive_ctrl_err(struct ctrl_pos *sp, struct ctrl_pos *pv)
>   ******************************************************************************/
>  
>  /* promote pages accessed through page tables */
> -static int folio_update_gen(struct folio *folio, int gen)
> +static int folio_update_gen(struct folio *folio, int gen, const vma_flags_t *vma_flags)
>  {
>  	unsigned long new_flags, old_flags = READ_ONCE(folio->flags.f);
>  
> @@ -3196,10 +3206,15 @@ static int folio_update_gen(struct folio *folio, int gen)
>  
>  	/* see the comment on LRU_REFS_FLAGS */
>  	if (!folio_test_referenced(folio) && !folio_test_workingset(folio)) {
> +		/* Activate file-backed executable folios after first usage. */
> +		if (is_exec_file_folio(folio, vma_flags))
> +			goto promote;
> +
>  		set_mask_bits(&folio->flags.f, LRU_REFS_MASK, BIT(PG_referenced));
>  		return -1;
>  	}
>  
> +promote:
>  	do {
>  		/* lru_gen_del_folio() has isolated this page? */
>  		if (!(old_flags & LRU_GEN_MASK))
> @@ -3428,8 +3443,8 @@ static bool suitable_to_scan(int total, int young)
>  	return young * n >= total;
>  }
>  
> -static void walk_update_folio(struct lru_gen_mm_walk *walk, struct folio *folio,
> -			      int new_gen, bool dirty)
> +static void walk_update_folio(struct lru_gen_mm_walk *walk, struct vm_area_struct *vma,
> +		struct folio *folio, int new_gen, bool dirty)
>  {
>  	int old_gen;
>  
> @@ -3442,10 +3457,10 @@ static void walk_update_folio(struct lru_gen_mm_walk *walk, struct folio *folio,
>  		folio_mark_dirty(folio);
>  
>  	if (walk) {
> -		old_gen = folio_update_gen(folio, new_gen);
> +		old_gen = folio_update_gen(folio, new_gen, &vma->flags);
>  		if (old_gen >= 0 && old_gen != new_gen)
>  			update_batch_size(walk, folio, old_gen, new_gen);
> -	} else if (lru_gen_set_refs(folio)) {
> +	} else if (lru_gen_set_refs(folio, &vma->flags)) {
>  		old_gen = folio_lru_gen(folio);
>  		if (old_gen >= 0 && old_gen != new_gen)
>  			folio_activate(folio);
> @@ -3518,7 +3533,7 @@ static bool walk_pte_range(pmd_t *pmd, unsigned long start, unsigned long end,
>  			continue;
>  
>  		if (last != folio) {
> -			walk_update_folio(walk, last, gen, dirty);
> +			walk_update_folio(walk, args->vma, last, gen, dirty);
>  
>  			last = folio;
>  			dirty = false;
> @@ -3531,7 +3546,7 @@ 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, last, gen, dirty);
> +	walk_update_folio(walk, args->vma, last, gen, dirty);
>  	last = NULL;
>  
>  	if (i < PTRS_PER_PTE && get_next_vma(PMD_MASK, PAGE_SIZE, args, &start, &end))
> @@ -3609,7 +3624,7 @@ static void walk_pmd_range_locked(pud_t *pud, unsigned long addr, struct vm_area
>  			goto next;
>  
>  		if (last != folio) {
> -			walk_update_folio(walk, last, gen, dirty);
> +			walk_update_folio(walk, vma, last, gen, dirty);
>  
>  			last = folio;
>  			dirty = false;
> @@ -3623,7 +3638,7 @@ 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, last, gen, dirty);
> +	walk_update_folio(walk, vma, last, gen, dirty);
>  
>  	lazy_mmu_mode_disable();
>  	spin_unlock(ptl);
> @@ -4258,7 +4273,7 @@ bool lru_gen_look_around(struct page_vma_mapped_walk *pvmw, unsigned int nr)
>  			continue;
>  
>  		if (last != folio) {
> -			walk_update_folio(walk, last, gen, dirty);
> +			walk_update_folio(walk, vma, last, gen, dirty);
>  
>  			last = folio;
>  			dirty = false;
> @@ -4270,7 +4285,7 @@ bool lru_gen_look_around(struct page_vma_mapped_walk *pvmw, unsigned int nr)
>  		young += nr;
>  	}
>  
> -	walk_update_folio(walk, last, gen, dirty);
> +	walk_update_folio(walk, vma, last, gen, dirty);
>  
>  	lazy_mmu_mode_disable();
>  
> -- 
> 2.47.3
>