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

[Kairui Song]

On Wed, Jul 15, 2026 at 2:33 PM Baolin Wang
<baolin.wang@xxxxxxxxxxxxxxxxx> wrote:

Hi Baolin,
>
> 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.

That's really a long history for those two commits :)
>
> 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() 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.
>
> Follow the classical LRU's logic, promoting mapped executable file folios
> after their first usage in folio_update_gen(), giving executable code a
> better chance to stay in memory.

Yeah I think that's mostly an ideology issue, recently upstream tends
to treat all folios fairly if there is no particular reason.
Personally I also agree that some folios are more special compared to
other though.

> 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
>
> Signed-off-by: Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx>
> ---
>  mm/vmscan.c | 25 +++++++++++++++----------
>  1 file changed, 15 insertions(+), 10 deletions(-)

MGLRU used to favor and put all map faulted memory at head, so could
this be related to a recent change in any way?
https://lore.kernel.org/linux-mm/20260526130938.66253-1-baohua@xxxxxxxxxx/

>
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index 986dde8e7429..429857852bdb 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -3188,7 +3188,7 @@ 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 vm_area_struct *vma, struct folio *folio, int gen)
>  {
>         unsigned long new_flags, old_flags = READ_ONCE(folio->flags.f);
>
> @@ -3196,10 +3196,15 @@ 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 (vma_test(vma, VMA_EXEC_BIT) && folio_is_file_lru(folio))
> +                       goto promote;
> +

Do you think it's a good idea to extract this into a helper e.g.
folio_is_executable_file?