Re: [PATCH v2] mm/khugepaged: alloc_charge_hpage() take care of mem charge errors

[Yang Shi]

On Wed, Feb 22, 2023 at 11:52 AM Peter Xu <peterx@xxxxxxxxxx> wrote:
>
> If memory charge failed, instead of returning the hpage but with an error,
> allow the function to cleanup the folio properly, which is normally what a
> function should do in this case - either return successfully, or return
> with no side effect of partial runs with an indicated error.
>
> This will also avoid the caller calling mem_cgroup_uncharge() unnecessarily
> with either anon or shmem path (even if it's safe to do so).

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

>
> Cc: Yang Shi <shy828301@xxxxxxxxx>
> Reviewed-by: David Stevens <stevensd@xxxxxxxxxxxx>
> Acked-by: Johannes Weiner <hannes@xxxxxxxxxxx>
> Signed-off-by: Peter Xu <peterx@xxxxxxxxxx>
> ---
> v1->v2:
> - Enhance commit message, drop "Fixes:" and "Cc: stable" tag, add R-bs.
> ---
>  mm/khugepaged.c | 9 ++++++++-
>  1 file changed, 8 insertions(+), 1 deletion(-)
>
> diff --git a/mm/khugepaged.c b/mm/khugepaged.c
> index 8dbc39896811..941d1c7ea910 100644
> --- a/mm/khugepaged.c
> +++ b/mm/khugepaged.c
> @@ -1063,12 +1063,19 @@ static int alloc_charge_hpage(struct page **hpage, struct mm_struct *mm,
>         gfp_t gfp = (cc->is_khugepaged ? alloc_hugepage_khugepaged_gfpmask() :
>                      GFP_TRANSHUGE);
>         int node = hpage_collapse_find_target_node(cc);
> +       struct folio *folio;
>
>         if (!hpage_collapse_alloc_page(hpage, gfp, node, &cc->alloc_nmask))
>                 return SCAN_ALLOC_HUGE_PAGE_FAIL;
> -       if (unlikely(mem_cgroup_charge(page_folio(*hpage), mm, gfp)))
> +
> +       folio = page_folio(*hpage);
> +       if (unlikely(mem_cgroup_charge(folio, mm, gfp))) {
> +               folio_put(folio);
> +               *hpage = NULL;
>                 return SCAN_CGROUP_CHARGE_FAIL;
> +       }
>         count_memcg_page_event(*hpage, THP_COLLAPSE_ALLOC);
> +
>         return SCAN_SUCCEED;
>  }
>
> --
> 2.39.1
>