Re: [PATCH] mm/khugepaged: Cleanup memcg uncharge for failure path

[Yang Shi]

On Fri, Mar 3, 2023 at 7:12 AM Peter Xu <peterx@xxxxxxxxxx> wrote:
>
> Explicit memcg uncharging is not needed when the memcg accounting has the
> same lifespan of the page/folio.  That becomes the case for khugepaged
> after Yang & Zach's recent rework so the hpage will be allocated for each
> collapse rather than being cached.
>
> Cleanup the explicit memcg uncharge in khugepaged failure path and leave
> that for put_page().

Thanks for the cleanup. Reviewed-by: Yang Shi <shy828301@xxxxxxxxx>

>
> Suggested-by: Zach O'Keefe <zokeefe@xxxxxxxxxx>
> Signed-off-by: Peter Xu <peterx@xxxxxxxxxx>
> ---
>  mm/khugepaged.c | 8 ++------
>  1 file changed, 2 insertions(+), 6 deletions(-)
>
> diff --git a/mm/khugepaged.c b/mm/khugepaged.c
> index 941d1c7ea910..dd5a7d9bc593 100644
> --- a/mm/khugepaged.c
> +++ b/mm/khugepaged.c
> @@ -1230,10 +1230,8 @@ static int collapse_huge_page(struct mm_struct *mm, unsigned long address,
>  out_up_write:
>         mmap_write_unlock(mm);
>  out_nolock:
> -       if (hpage) {
> -               mem_cgroup_uncharge(page_folio(hpage));
> +       if (hpage)
>                 put_page(hpage);
> -       }
>         trace_mm_collapse_huge_page(mm, result == SCAN_SUCCEED, result);
>         return result;
>  }
> @@ -2250,10 +2248,8 @@ static int collapse_file(struct mm_struct *mm, unsigned long addr,
>                 unlock_page(hpage);
>  out:
>         VM_BUG_ON(!list_empty(&pagelist));
> -       if (hpage) {
> -               mem_cgroup_uncharge(page_folio(hpage));
> +       if (hpage)
>                 put_page(hpage);
> -       }
>
>         trace_mm_khugepaged_collapse_file(mm, hpage, index, is_shmem, addr, file, nr, result);
>         return result;
> --
> 2.39.1
>