Date:   Tue, 2 Mar 2021 12:12:16 +0800
From:   Muchun Song <songmuchun@...edance.com>
To:     Roman Gushchin <guro@...com>
Cc:     Alexander Viro <viro@...iv.linux.org.uk>, Jan Kara <jack@...e.cz>,
        Amir Goldstein <amir73il@...il.com>,
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        Xiongchun duan <duanxiongchun@...edance.com>
Subject: Re: [External] Re: [PATCH 4/5] mm: memcontrol: move remote memcg
 charging APIs to CONFIG_MEMCG_KMEM

On Tue, Mar 2, 2021 at 9:15 AM Roman Gushchin <guro@...com> wrote:
>
> On Mon, Mar 01, 2021 at 02:22:26PM +0800, Muchun Song wrote:
> > The remote memcg charing APIs is a mechanism to charge kernel memory
> > to a given memcg. So we can move the infrastructure to the scope of
> > the CONFIG_MEMCG_KMEM.
>
> This is not a good idea, because there is nothing kmem-specific
> in the idea of remote charging, and we definitely will see cases
> when user memory is charged to the process different from the current.

Got it. Thanks for your reminder.


>
> >
> > As a bonus, on !CONFIG_MEMCG_KMEM build some functions and variables
> > can be compiled out.
> >
> > Signed-off-by: Muchun Song <songmuchun@...edance.com>
> > ---
> >  include/linux/sched.h    | 2 ++
> >  include/linux/sched/mm.h | 2 +-
> >  kernel/fork.c            | 2 +-
> >  mm/memcontrol.c          | 4 ++++
> >  4 files changed, 8 insertions(+), 2 deletions(-)
> >
> > diff --git a/include/linux/sched.h b/include/linux/sched.h
> > index ee46f5cab95b..c2d488eddf85 100644
> > --- a/include/linux/sched.h
> > +++ b/include/linux/sched.h
> > @@ -1314,7 +1314,9 @@ struct task_struct {
> >
> >       /* Number of pages to reclaim on returning to userland: */
> >       unsigned int                    memcg_nr_pages_over_high;
> > +#endif
> >
> > +#ifdef CONFIG_MEMCG_KMEM
> >       /* Used by memcontrol for targeted memcg charge: */
> >       struct mem_cgroup               *active_memcg;
> >  #endif
> > diff --git a/include/linux/sched/mm.h b/include/linux/sched/mm.h
> > index 1ae08b8462a4..64a72975270e 100644
> > --- a/include/linux/sched/mm.h
> > +++ b/include/linux/sched/mm.h
> > @@ -294,7 +294,7 @@ static inline void memalloc_nocma_restore(unsigned int flags)
> >  }
> >  #endif
> >
> > -#ifdef CONFIG_MEMCG
> > +#ifdef CONFIG_MEMCG_KMEM
> >  DECLARE_PER_CPU(struct mem_cgroup *, int_active_memcg);
> >  /**
> >   * set_active_memcg - Starts the remote memcg charging scope.
> > diff --git a/kernel/fork.c b/kernel/fork.c
> > index d66cd1014211..d66718bc82d5 100644
> > --- a/kernel/fork.c
> > +++ b/kernel/fork.c
> > @@ -942,7 +942,7 @@ static struct task_struct *dup_task_struct(struct task_struct *orig, int node)
> >       tsk->use_memdelay = 0;
> >  #endif
> >
> > -#ifdef CONFIG_MEMCG
> > +#ifdef CONFIG_MEMCG_KMEM
> >       tsk->active_memcg = NULL;
> >  #endif
> >       return tsk;
> > diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> > index 39cb8c5bf8b2..092dc4588b43 100644
> > --- a/mm/memcontrol.c
> > +++ b/mm/memcontrol.c
> > @@ -76,8 +76,10 @@ EXPORT_SYMBOL(memory_cgrp_subsys);
> >
> >  struct mem_cgroup *root_mem_cgroup __read_mostly;
> >
> > +#ifdef CONFIG_MEMCG_KMEM
> >  /* Active memory cgroup to use from an interrupt context */
> >  DEFINE_PER_CPU(struct mem_cgroup *, int_active_memcg);
> > +#endif
> >
> >  /* Socket memory accounting disabled? */
> >  static bool cgroup_memory_nosocket;
> > @@ -1054,6 +1056,7 @@ struct mem_cgroup *get_mem_cgroup_from_mm(struct mm_struct *mm)
> >  }
> >  EXPORT_SYMBOL(get_mem_cgroup_from_mm);
> >
> > +#ifdef CONFIG_MEMCG_KMEM
> >  static __always_inline struct mem_cgroup *active_memcg(void)
> >  {
> >       if (in_interrupt())
> > @@ -1074,6 +1077,7 @@ static __always_inline bool memcg_kmem_bypass(void)
> >
> >       return false;
> >  }
> > +#endif
> >
> >  /**
> >   * mem_cgroup_iter - iterate over memory cgroup hierarchy
> > --
> > 2.11.0
> >

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