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Message-ID: <YEKLIUcPfpKYtFLA@carbon.dhcp.thefacebook.com>
Date: Fri, 5 Mar 2021 11:48:49 -0800
From: Roman Gushchin <guro@...com>
To: Muchun Song <songmuchun@...edance.com>
CC: <hannes@...xchg.org>, <mhocko@...nel.org>,
<akpm@...ux-foundation.org>, <shakeelb@...gle.com>,
<vdavydov.dev@...il.com>, <linux-kernel@...r.kernel.org>,
<linux-mm@...ck.org>, <duanxiongchun@...edance.com>
Subject: Re: [PATCH v2 4/5] mm: memcontrol: introduce remote objcg charging
API
On Wed, Mar 03, 2021 at 01:59:16PM +0800, Muchun Song wrote:
> The remote memcg charing APIs is a mechanism to charge pages to a given
> memcg. Since all kernel memory are charged by using obj_cgroup APIs.
> Actually, we want to charge kernel memory to the remote object cgroup
> instead of memory cgroup. So introduce remote objcg charging APIs to
> charge the kmem pages by using objcg_cgroup APIs. And if remote memcg
> and objcg are both set, objcg takes precedence over memcg to charge
> the kmem pages.
>
> In the later patch, we will use those API to charge kernel memory to
> the remote objcg.
I'd abandon/postpone the rest of the patchset (patches 4 and 5) as now.
They add a lot of new code to solve a theoretical problem (please, fix
me if I'm wrong), which is not a panic or data corruption, but
a sub-optimal garbage collection behavior. I think we need a better
motivation or/and an implementation which makes the code simpler
and smaller.
>
> Signed-off-by: Muchun Song <songmuchun@...edance.com>
> ---
> include/linux/sched.h | 4 ++++
> include/linux/sched/mm.h | 38 ++++++++++++++++++++++++++++++++++++++
> kernel/fork.c | 3 +++
> mm/memcontrol.c | 44 ++++++++++++++++++++++++++++++++++++++++----
> 4 files changed, 85 insertions(+), 4 deletions(-)
>
> diff --git a/include/linux/sched.h b/include/linux/sched.h
> index ee46f5cab95b..8edcc71a0a1d 100644
> --- a/include/linux/sched.h
> +++ b/include/linux/sched.h
> @@ -1318,6 +1318,10 @@ struct task_struct {
> /* Used by memcontrol for targeted memcg charge: */
> struct mem_cgroup *active_memcg;
> #endif
> +#ifdef CONFIG_MEMCG_KMEM
> + /* Used by memcontrol for targeted objcg charge: */
> + struct obj_cgroup *active_objcg;
> +#endif
>
> #ifdef CONFIG_BLK_CGROUP
> struct request_queue *throttle_queue;
> diff --git a/include/linux/sched/mm.h b/include/linux/sched/mm.h
> index 1ae08b8462a4..be1189598b09 100644
> --- a/include/linux/sched/mm.h
> +++ b/include/linux/sched/mm.h
> @@ -330,6 +330,44 @@ set_active_memcg(struct mem_cgroup *memcg)
> }
> #endif
>
> +#ifdef CONFIG_MEMCG_KMEM
> +DECLARE_PER_CPU(struct obj_cgroup *, int_active_objcg);
> +
> +/**
> + * set_active_objcg - Starts the remote objcg kmem pages charging scope.
> + * @objcg: objcg to charge.
> + *
> + * This function marks the beginning of the remote objcg charging scope. All the
> + * __GFP_ACCOUNT kmem page allocations till the end of the scope will be charged
> + * to the given objcg.
> + *
> + * NOTE: This function can nest. Users must save the return value and
> + * reset the previous value after their own charging scope is over.
> + *
> + * If remote memcg and objcg are both set, objcg takes precedence over memcg
> + * to charge the kmem pages.
> + */
> +static inline struct obj_cgroup *set_active_objcg(struct obj_cgroup *objcg)
> +{
> + struct obj_cgroup *old;
> +
> + if (in_interrupt()) {
> + old = this_cpu_read(int_active_objcg);
> + this_cpu_write(int_active_objcg, objcg);
> + } else {
> + old = current->active_objcg;
> + current->active_objcg = objcg;
> + }
> +
> + return old;
> +}
> +#else
> +static inline struct obj_cgroup *set_active_objcg(struct obj_cgroup *objcg)
> +{
> + return NULL;
> +}
> +#endif
> +
> #ifdef CONFIG_MEMBARRIER
> enum {
> MEMBARRIER_STATE_PRIVATE_EXPEDITED_READY = (1U << 0),
> diff --git a/kernel/fork.c b/kernel/fork.c
> index d66cd1014211..b4b9dd5d122f 100644
> --- a/kernel/fork.c
> +++ b/kernel/fork.c
> @@ -945,6 +945,9 @@ static struct task_struct *dup_task_struct(struct task_struct *orig, int node)
> #ifdef CONFIG_MEMCG
> tsk->active_memcg = NULL;
> #endif
> +#ifdef CONFIG_MEMCG_KMEM
> + tsk->active_objcg = NULL;
> +#endif
> return tsk;
>
> free_stack:
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index 0cf342d22547..e48d4ab0af76 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -79,6 +79,11 @@ struct mem_cgroup *root_mem_cgroup __read_mostly;
> /* Active memory cgroup to use from an interrupt context */
> DEFINE_PER_CPU(struct mem_cgroup *, int_active_memcg);
>
> +#ifdef CONFIG_MEMCG_KMEM
> +/* Active object cgroup to use from an interrupt context */
> +DEFINE_PER_CPU(struct obj_cgroup *, int_active_objcg);
> +#endif
> +
> /* Socket memory accounting disabled? */
> static bool cgroup_memory_nosocket;
>
> @@ -1076,7 +1081,7 @@ static __always_inline struct mem_cgroup *get_active_memcg(void)
> return memcg;
> }
>
> -static __always_inline bool memcg_kmem_bypass(void)
> +static __always_inline bool memcg_charge_bypass(void)
> {
> /* Allow remote memcg charging from any context. */
> if (unlikely(active_memcg()))
> @@ -1094,7 +1099,7 @@ static __always_inline bool memcg_kmem_bypass(void)
> */
> static __always_inline struct mem_cgroup *get_mem_cgroup_from_current(void)
> {
> - if (memcg_kmem_bypass())
> + if (memcg_charge_bypass())
> return NULL;
>
> if (unlikely(active_memcg()))
> @@ -1103,6 +1108,29 @@ static __always_inline struct mem_cgroup *get_mem_cgroup_from_current(void)
> return get_mem_cgroup_from_mm(current->mm);
> }
>
> +#ifdef CONFIG_MEMCG_KMEM
> +static __always_inline struct obj_cgroup *active_objcg(void)
> +{
> + if (in_interrupt())
> + return this_cpu_read(int_active_objcg);
> + else
> + return current->active_objcg;
> +}
> +
> +static __always_inline bool kmem_charge_bypass(void)
> +{
> + /* Allow remote charging from any context. */
> + if (unlikely(active_objcg() || active_memcg()))
> + return false;
> +
> + /* Memcg to charge can't be determined. */
> + if (in_interrupt() || !current->mm || (current->flags & PF_KTHREAD))
> + return true;
> +
> + return false;
> +}
> +#endif
> +
> /**
> * mem_cgroup_iter - iterate over memory cgroup hierarchy
> * @root: hierarchy root
> @@ -2997,13 +3025,20 @@ struct mem_cgroup *mem_cgroup_from_obj(void *p)
>
> __always_inline struct obj_cgroup *get_obj_cgroup_from_current(void)
> {
> - struct obj_cgroup *objcg = NULL;
> + struct obj_cgroup *objcg;
> struct mem_cgroup *memcg;
>
> - if (memcg_kmem_bypass())
> + if (kmem_charge_bypass())
> return NULL;
>
> rcu_read_lock();
> + objcg = active_objcg();
> + if (unlikely(objcg)) {
> + /* remote object cgroup must hold a reference. */
> + obj_cgroup_get(objcg);
> + goto out;
> + }
> +
> if (unlikely(active_memcg()))
> memcg = active_memcg();
> else
> @@ -3015,6 +3050,7 @@ __always_inline struct obj_cgroup *get_obj_cgroup_from_current(void)
> break;
> objcg = NULL;
> }
> +out:
> rcu_read_unlock();
>
> return objcg;
> --
> 2.11.0
>
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