Re: [PATCH 2/3] mm, memcg: inline mem_cgroup_{charge/uncharge} to improve disabled memcg config

[Suren Baghdasaryan]

On Fri, Jul 9, 2021 at 7:48 AM Johannes Weiner <hannes@xxxxxxxxxxx> wrote:
>
> On Thu, Jul 08, 2021 at 05:05:08PM -0700, Suren Baghdasaryan wrote:
> > Inline mem_cgroup_{charge/uncharge} and mem_cgroup_uncharge_list functions
> > functions to perform mem_cgroup_disabled static key check inline before
> > calling the main body of the function. This minimizes the memcg overhead
> > in the pagefault and exit_mmap paths when memcgs are disabled using
> > cgroup_disable=memory command-line option.
> > This change results in ~0.4% overhead reduction when running PFT test
> > comparing {CONFIG_MEMCG=n} against {CONFIG_MEMCG=y, cgroup_disable=memory}
> > configurationon on an 8-core ARM64 Android device.
> >
> > Signed-off-by: Suren Baghdasaryan <surenb@xxxxxxxxxx>
>
> Sounds reasonable to me as well. One comment:
>
> > @@ -693,13 +693,59 @@ static inline bool mem_cgroup_below_min(struct mem_cgroup *memcg)
> >               page_counter_read(&memcg->memory);
> >  }
> >
> > -int mem_cgroup_charge(struct page *page, struct mm_struct *mm, gfp_t gfp_mask);
> > +struct mem_cgroup *get_mem_cgroup_from_mm(struct mm_struct *mm);
> > +
> > +int __mem_cgroup_charge(struct page *page, struct mem_cgroup *memcg,
> > +                     gfp_t gfp);
> > +/**
> > + * mem_cgroup_charge - charge a newly allocated page to a cgroup
> > + * @page: page to charge
> > + * @mm: mm context of the victim
> > + * @gfp_mask: reclaim mode
> > + *
> > + * Try to charge @page to the memcg that @mm belongs to, reclaiming
> > + * pages according to @gfp_mask if necessary. if @mm is NULL, try to
> > + * charge to the active memcg.
> > + *
> > + * Do not use this for pages allocated for swapin.
> > + *
> > + * Returns 0 on success. Otherwise, an error code is returned.
> > + */
> > +static inline int mem_cgroup_charge(struct page *page, struct mm_struct *mm,
> > +                                 gfp_t gfp_mask)
> > +{
> > +     struct mem_cgroup *memcg;
> > +     int ret;
> > +
> > +     if (mem_cgroup_disabled())
> > +             return 0;
> > +
> > +     memcg = get_mem_cgroup_from_mm(mm);
> > +     ret = __mem_cgroup_charge(page, memcg, gfp_mask);
> > +     css_put(&memcg->css);
> > +
> > +     return ret;
>
> Why not do
>
> int __mem_cgroup_charge(struct page *page, struct mm_struct *mm,
>                         gfp_t gfp_mask);
>
> static inline int mem_cgroup_charge(struct page *page, struct mm_struct *mm,
>                                     gfp_t gfp_mask)
> {
>         if (mem_cgroup_disabled())
>                 return 0;
>
>         return __mem_cgroup_charge(page, memcg, gfp_mask);
> }
>
> like in the other cases as well?
>
> That would avoid inlining two separate function calls into all the
> callsites...
>
> There is an (internal) __mem_cgroup_charge() already, but you can
> rename it charge_memcg().

Sounds good. I'll post an updated version with your suggestion.
Thanks for the review, Johannes!

>