Re: [PATCH v4] mm: shrink skip folio mapped by an exiting task

[Barry Song]

On Mon, Jul 8, 2024 at 3:15 PM Zhiguo Jiang <justinjiang@xxxxxxxx> wrote:
>
> If an anon folio reclaimed by shrink_inactive_list is mapped by an
> exiting task, this anon folio will be firstly swaped-out into
> swapspace in shrink flow and then this swap folio is freed in task
> exit flow. But if this folio mapped by an exiting task can skip
> shrink and be freed directly in task exiting flow, which will save
> swap-out time and alleviate the load of the tasks exiting process.
> The file folio is also similar.
>
> And when system is low memory, it more likely to occur, because more
> backend applidatuions will be killed.
>
> This patch can alleviate the cpu load of the tasks exiting process.
>
> Signed-off-by: Qianfeng Rong <rongqianfeng@xxxxxxxxxxxxxxxxxxxxxxxxxxxx>
> ---
>
> Change log:
> v3->v4:
> 1.Modify that the unshared folios mapped only in exiting task are skip.
> v2->v3:
> Nothing.
> v1->v2:
> 1.The VM_EXITING added in v1 patch is removed, because it will fail
> to compile in 32-bit system.
>
> Signed-off-by: Zhiguo Jiang <justinjiang@xxxxxxxx>
> ---
>  mm/rmap.c | 10 ++++++++++
>  1 file changed, 10 insertions(+)
>  mode change 100644 => 100755 mm/rmap.c
>
> diff --git a/mm/rmap.c b/mm/rmap.c
> index 26806b49a86f..16b7ed04bcbe
> --- a/mm/rmap.c
> +++ b/mm/rmap.c
> @@ -843,6 +843,16 @@ static bool folio_referenced_one(struct folio *folio,
>         int referenced = 0;
>         unsigned long start = address, ptes = 0;
>
> +       /* Skip the unshared folios mapped only by the single
> +        * exiting process.
> +        */
> +       if ((!atomic_read(&vma->vm_mm->mm_users) ||
> +               test_bit(MMF_OOM_SKIP, &vma->vm_mm->flags)) &&
> +               !test_bit(VM_SHARED, &vma->vm_flags)) {

I don't think this is correct. folio_likely_mapped_shared() is almost "correct"
but not always.

> +               pra->referenced = -1;

Please explain why you set  pra->referenced =  -1. Please address all
comments before you send a new version.

> +               return false;
> +       }
> +
>         while (page_vma_mapped_walk(&pvmw)) {
>                 address = pvmw.address;
>
> --
> 2.39.0
>

Thanks
Barry