linux-kernel - Re: [PATCH] mm/page_alloc: simplify kmem cgroup charge/uncharge code

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Date:   Mon, 7 Dec 2020 09:28:46 -0800
From:   Shakeel Butt <shakeelb@...gle.com>
To:     Hui Su <sh_def@....com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Linux MM <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Muchun Song <songmuchun@...edance.com>
Subject: Re: [PATCH] mm/page_alloc: simplify kmem cgroup charge/uncharge code

On Mon, Dec 7, 2020 at 6:22 AM Hui Su <sh_def@....com> wrote:
>
> Since the commit 60cd4bcd6238 ("memcg: localize memcg_kmem_enabled()
> check"), we have supplied the api which users don't have to explicitly
> check memcg_kmem_enabled().
>
> Signed-off-by: Hui Su <sh_def@....com>
> ---
>  mm/page_alloc.c | 12 ++++++------
>  1 file changed, 6 insertions(+), 6 deletions(-)
>
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index eaa227a479e4..dc990a899ded 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -1214,8 +1214,8 @@ static __always_inline bool free_pages_prepare(struct page *page,
>                  * Do not let hwpoison pages hit pcplists/buddy
>                  * Untie memcg state and reset page's owner
>                  */
> -               if (memcg_kmem_enabled() && PageKmemcg(page))
> -                       __memcg_kmem_uncharge_page(page, order);
> +               if (PageKmemcg(page))
> +                       memcg_kmem_uncharge_page(page, order);
>                 reset_page_owner(page, order);
>                 return false;
>         }
> @@ -1244,8 +1244,8 @@ static __always_inline bool free_pages_prepare(struct page *page,
>         }
>         if (PageMappingFlags(page))
>                 page->mapping = NULL;
> -       if (memcg_kmem_enabled() && PageKmemcg(page))
> -               __memcg_kmem_uncharge_page(page, order);
> +       if (PageKmemcg(page))
> +               memcg_kmem_uncharge_page(page, order);
>         if (check_free)
>                 bad += check_free_page(page);
>         if (bad)
> @@ -4965,8 +4965,8 @@ __alloc_pages_nodemask(gfp_t gfp_mask, unsigned int order, int preferred_nid,
>         page = __alloc_pages_slowpath(alloc_mask, order, &ac);
>
>  out:
> -       if (memcg_kmem_enabled() && (gfp_mask & __GFP_ACCOUNT) && page &&
> -           unlikely(__memcg_kmem_charge_page(page, gfp_mask, order) != 0)) {
> +       if ((gfp_mask & __GFP_ACCOUNT) && page &&
> +           unlikely(memcg_kmem_charge_page(page, gfp_mask, order) != 0)) {
>                 __free_pages(page, order);
>                 page = NULL;
>         }


The reason to keep __memcg_kmem_[un]charge_page functions is that they
were called in the very hot path. Can you please check the performance
impact of your change and if the generated code is actually same or
different.