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References: <20230303151218.311015-1-peterx@redhat.com>
In-Reply-To: <20230303151218.311015-1-peterx@redhat.com>
From:   Yang Shi <shy828301@gmail.com>
Date:   Fri, 3 Mar 2023 11:00:24 -0800
Message-ID: <CAHbLzkog36Ch2Ys8+ZOjbpug68p5XLjt-0Mc1TBVuNAirqRW+A@mail.gmail.com>
Subject: Re: [PATCH] mm/khugepaged: Cleanup memcg uncharge for failure path
To:     Peter Xu <peterx@redhat.com>
Cc:     linux-mm@kvack.org, linux-kernel@vger.kernel.org,
        David Stevens <stevensd@chromium.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Johannes Weiner <hannes@cmpxchg.org>,
        "Zach O'Keefe" <zokeefe@google.com>
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On Fri, Mar 3, 2023 at 7:12=E2=80=AFAM Peter Xu <peterx@redhat.com> 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@gmail.com>

>
> Suggested-by: Zach O'Keefe <zokeefe@google.com>
> Signed-off-by: Peter Xu <peterx@redhat.com>
> ---
>  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 =3D=3D SCAN_SUCCEED, resul=
t);
>         return result;
>  }
> @@ -2250,10 +2248,8 @@ static int collapse_file(struct mm_struct *mm, uns=
igned 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, add=
r, file, nr, result);
>         return result;
> --
> 2.39.1
>