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

[Kairui Song]

On Fri, Jul 17, 2026 at 6:06 PM Baolin Wang
<baolin.wang@xxxxxxxxxxxxxxxxx> 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>
> ---
>  mm/vmscan.c | 47 +++++++++++++++++++++++++++++++----------------
>  1 file changed, 31 insertions(+), 16 deletions(-)

Hi Baolin, thanks for the update, looks good to me with two nit picks:
>
> 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;
> +

This somehow missed the PG_workingset below?

>                 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;
> +

Will it be cleaner if we just:

/*
* See the comment on LRU_REFS_FLAGS, and we protect the executable
* parts to avoid typical IO thrashing from reclaiming.
*/
if (!folio_test_referenced(folio) && !folio_test_workingset(folio) &&
    !is_exec_file_folio(folio, vma_flags)) {
    set_mask_bits(&folio->flags.f, LRU_REFS_MASK, BIT(PG_referenced));
    return -1;
}

If we use same check above we also get the PG_workingset?