Re: [PATCH V5 04/10] Infrastructure to support per-memcg reclaim.

[Minchan Kim <minchan.kim@gmail.com>]

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On Sat, Apr 16, 2011 at 8:23 AM, Ying Han <yinghan@google.com> wrote:
> Add the kswapd_mem field in kswapd descriptor which links the kswapd
> kernel thread to a memcg. The per-memcg kswapd is sleeping in the wait
> queue headed at kswapd_wait field of the kswapd descriptor.
>
> The kswapd() function is now shared between global and per-memcg kswapd. It
> is passed in with the kswapd descriptor which contains the information of
> either node or memcg. Then the new function balance_mem_cgroup_pgdat is
> invoked if it is per-mem kswapd thread, and the implementation of the function
> is on the following patch.
>
> changelog v4..v3:
> 1. fix up the kswapd_run and kswapd_stop for online_pages() and offline_pages.
> 2. drop the PF_MEMALLOC flag for memcg kswapd for now per KAMAZAWA's request.
>
> changelog v3..v2:
> 1. split off from the initial patch which includes all changes of the following
> three patches.
>
> Signed-off-by: Ying Han <yinghan@google.com>
> ---
>  include/linux/memcontrol.h |    5 ++
>  include/linux/swap.h       |    5 +-
>  mm/memcontrol.c            |   29 ++++++++
>  mm/memory_hotplug.c        |    4 +-
>  mm/vmscan.c                |  156 ++++++++++++++++++++++++++++++--------------
>  5 files changed, 147 insertions(+), 52 deletions(-)
>
> diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
> index 3ece36d..f7ffd1f 100644
> --- a/include/linux/memcontrol.h
> +++ b/include/linux/memcontrol.h
> @@ -24,6 +24,7 @@ struct mem_cgroup;
>  struct page_cgroup;
>  struct page;
>  struct mm_struct;
> +struct kswapd;
>
>  /* Stats that can be updated by kernel. */
>  enum mem_cgroup_page_stat_item {
> @@ -83,6 +84,10 @@ int task_in_mem_cgroup(struct task_struct *task, const struct mem_cgroup *mem);
>  extern struct mem_cgroup *try_get_mem_cgroup_from_page(struct page *page);
>  extern struct mem_cgroup *mem_cgroup_from_task(struct task_struct *p);
>  extern int mem_cgroup_watermark_ok(struct mem_cgroup *mem, int charge_flags);
> +extern int mem_cgroup_init_kswapd(struct mem_cgroup *mem,
> +                                 struct kswapd *kswapd_p);
> +extern void mem_cgroup_clear_kswapd(struct mem_cgroup *mem);
> +extern wait_queue_head_t *mem_cgroup_kswapd_wait(struct mem_cgroup *mem);
>
>  static inline
>  int mm_match_cgroup(const struct mm_struct *mm, const struct mem_cgroup *cgroup)
> diff --git a/include/linux/swap.h b/include/linux/swap.h
> index f43d406..17e0511 100644
> --- a/include/linux/swap.h
> +++ b/include/linux/swap.h
> @@ -30,6 +30,7 @@ struct kswapd {
>        struct task_struct *kswapd_task;
>        wait_queue_head_t kswapd_wait;
>        pg_data_t *kswapd_pgdat;
> +       struct mem_cgroup *kswapd_mem;
>  };
>
>  int kswapd(void *p);
> @@ -303,8 +304,8 @@ static inline void scan_unevictable_unregister_node(struct node *node)
>  }
>  #endif
>
> -extern int kswapd_run(int nid);
> -extern void kswapd_stop(int nid);
> +extern int kswapd_run(int nid, struct mem_cgroup *mem);
> +extern void kswapd_stop(int nid, struct mem_cgroup *mem);
>
>  #ifdef CONFIG_MMU
>  /* linux/mm/shmem.c */
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index 76ad009..8761a6f 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -278,6 +278,8 @@ struct mem_cgroup {
>         */
>        u64 high_wmark_distance;
>        u64 low_wmark_distance;
> +
> +       wait_queue_head_t *kswapd_wait;


Like I mentioned in [1/10], personally, I like including kswapd
instead of kswapd_wait. Just personal opinion. Feel free to ignore.

>  };
>
>  /* Stuffs for move charges at task migration. */
> @@ -4670,6 +4672,33 @@ int mem_cgroup_watermark_ok(struct mem_cgroup *mem,
>        return ret;
>  }
>
> +int mem_cgroup_init_kswapd(struct mem_cgroup *mem, struct kswapd *kswapd_p)
> +{
> +       if (!mem || !kswapd_p)
> +               return 0;
> +
> +       mem->kswapd_wait = &kswapd_p->kswapd_wait;
> +       kswapd_p->kswapd_mem = mem;
> +
> +       return css_id(&mem->css);
> +}
> +
> +void mem_cgroup_clear_kswapd(struct mem_cgroup *mem)
> +{
> +       if (mem)
> +               mem->kswapd_wait = NULL;
> +
> +       return;
> +}
> +
> +wait_queue_head_t *mem_cgroup_kswapd_wait(struct mem_cgroup *mem)
> +{
> +       if (!mem)
> +               return NULL;
> +
> +       return mem->kswapd_wait;
> +}
> +
>  static int mem_cgroup_soft_limit_tree_init(void)
>  {
>        struct mem_cgroup_tree_per_node *rtpn;
> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> index 321fc74..2f78ff6 100644
> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -462,7 +462,7 @@ int online_pages(unsigned long pfn, unsigned long nr_pages)
>        setup_per_zone_wmarks();
>        calculate_zone_inactive_ratio(zone);
>        if (onlined_pages) {
> -               kswapd_run(zone_to_nid(zone));
> +               kswapd_run(zone_to_nid(zone), NULL);
>                node_set_state(zone_to_nid(zone), N_HIGH_MEMORY);
>        }
>
> @@ -897,7 +897,7 @@ repeat:
>        calculate_zone_inactive_ratio(zone);
>        if (!node_present_pages(node)) {
>                node_clear_state(node, N_HIGH_MEMORY);
> -               kswapd_stop(node);
> +               kswapd_stop(node, NULL);
>        }
>
>        vm_total_pages = nr_free_pagecache_pages();
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index 61fb96e..06036d2 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -2241,6 +2241,8 @@ static bool pgdat_balanced(pg_data_t *pgdat, unsigned long balanced_pages,
>        return balanced_pages > (present_pages >> 2);
>  }
>
> +#define is_node_kswapd(kswapd_p) (!(kswapd_p)->kswapd_mem)

In memcg, we already have a similar thing "scanning_global_lru".
How about using "global" term?

> +
>  /* is kswapd sleeping prematurely? */
>  static int sleeping_prematurely(struct kswapd *kswapd, int order,
>                                long remaining, int classzone_idx)
> @@ -2249,11 +2251,16 @@ static int sleeping_prematurely(struct kswapd *kswapd, int order,
>        unsigned long balanced = 0;
>        bool all_zones_ok = true;
>        pg_data_t *pgdat = kswapd->kswapd_pgdat;
> +       struct mem_cgroup *mem = kswapd->kswapd_mem;
>
>        /* If a direct reclaimer woke kswapd within HZ/10, it's premature */
>        if (remaining)
>                return true;
>
> +       /* Doesn't support for per-memcg reclaim */
> +       if (mem)
> +               return false;
> +

How about is_global_kswapd instead of checking wheterh mem field is NULL or not?

>        /* Check the watermark levels */
>        for (i = 0; i < pgdat->nr_zones; i++) {
>                struct zone *zone = pgdat->node_zones + i;
> @@ -2596,19 +2603,25 @@ static void kswapd_try_to_sleep(struct kswapd *kswapd_p, int order,
>         * go fully to sleep until explicitly woken up.
>         */
>        if (!sleeping_prematurely(kswapd_p, order, remaining, classzone_idx)) {
> -               trace_mm_vmscan_kswapd_sleep(pgdat->node_id);
> +               if (is_node_kswapd(kswapd_p)) {
> +                       trace_mm_vmscan_kswapd_sleep(pgdat->node_id);
>
> -               /*
> -                * vmstat counters are not perfectly accurate and the estimated
> -                * value for counters such as NR_FREE_PAGES can deviate from the
> -                * true value by nr_online_cpus * threshold. To avoid the zone
> -                * watermarks being breached while under pressure, we reduce the
> -                * per-cpu vmstat threshold while kswapd is awake and restore
> -                * them before going back to sleep.
> -                */
> -               set_pgdat_percpu_threshold(pgdat, calculate_normal_threshold);
> -               schedule();
> -               set_pgdat_percpu_threshold(pgdat, calculate_pressure_threshold);
> +                       /*
> +                        * vmstat counters are not perfectly accurate and the
> +                        * estimated value for counters such as NR_FREE_PAGES
> +                        * can deviate from the true value by nr_online_cpus *
> +                        * threshold. To avoid the zone watermarks being
> +                        * breached while under pressure, we reduce the per-cpu
> +                        * vmstat threshold while kswapd is awake and restore
> +                        * them before going back to sleep.
> +                        */
> +                       set_pgdat_percpu_threshold(pgdat,
> +                                                  calculate_normal_threshold);
> +                       schedule();
> +                       set_pgdat_percpu_threshold(pgdat,
> +                                               calculate_pressure_threshold);
> +               } else
> +                       schedule();
>        } else {
>                if (remaining)
>                        count_vm_event(KSWAPD_LOW_WMARK_HIT_QUICKLY);
> @@ -2618,6 +2631,12 @@ static void kswapd_try_to_sleep(struct kswapd *kswapd_p, int order,
>        finish_wait(wait_h, &wait);
>  }
>
> +static unsigned long balance_mem_cgroup_pgdat(struct mem_cgroup *mem_cont,
> +                                                       int order)
> +{
> +       return 0;
> +}
> +
>  /*
>  * The background pageout daemon, started as a kernel thread
>  * from the init process.
> @@ -2637,6 +2656,7 @@ int kswapd(void *p)
>        int classzone_idx;
>        struct kswapd *kswapd_p = (struct kswapd *)p;
>        pg_data_t *pgdat = kswapd_p->kswapd_pgdat;
> +       struct mem_cgroup *mem = kswapd_p->kswapd_mem;
>        wait_queue_head_t *wait_h = &kswapd_p->kswapd_wait;
>        struct task_struct *tsk = current;
>
> @@ -2647,10 +2667,12 @@ int kswapd(void *p)
>
>        lockdep_set_current_reclaim_state(GFP_KERNEL);
>
> -       BUG_ON(pgdat->kswapd_wait != wait_h);
> -       cpumask = cpumask_of_node(pgdat->node_id);
> -       if (!cpumask_empty(cpumask))
> -               set_cpus_allowed_ptr(tsk, cpumask);
> +       if (is_node_kswapd(kswapd_p)) {
> +               BUG_ON(pgdat->kswapd_wait != wait_h);
> +               cpumask = cpumask_of_node(pgdat->node_id);
> +               if (!cpumask_empty(cpumask))
> +                       set_cpus_allowed_ptr(tsk, cpumask);
> +       }
>        current->reclaim_state = &reclaim_state;
>
>        /*
> @@ -2665,7 +2687,10 @@ int kswapd(void *p)
>         * us from recursively trying to free more memory as we're
>         * trying to free the first piece of memory in the first place).
>         */
> -       tsk->flags |= PF_MEMALLOC | PF_SWAPWRITE | PF_KSWAPD;
> +       if (is_node_kswapd(kswapd_p))
> +               tsk->flags |= PF_MEMALLOC | PF_SWAPWRITE | PF_KSWAPD;
> +       else
> +               tsk->flags |= PF_SWAPWRITE | PF_KSWAPD;
>        set_freezable();
>
>        order = 0;
> @@ -2675,24 +2700,29 @@ int kswapd(void *p)
>                int new_classzone_idx;
>                int ret;
>
> -               new_order = pgdat->kswapd_max_order;
> -               new_classzone_idx = pgdat->classzone_idx;
> -               pgdat->kswapd_max_order = 0;
> -               pgdat->classzone_idx = MAX_NR_ZONES - 1;
> -               if (order < new_order || classzone_idx > new_classzone_idx) {
> -                       /*
> -                        * Don't sleep if someone wants a larger 'order'
> -                        * allocation or has tigher zone constraints
> -                        */
> -                       order = new_order;
> -                       classzone_idx = new_classzone_idx;
> -               } else {
> -                       kswapd_try_to_sleep(kswapd_p, order, classzone_idx);
> -                       order = pgdat->kswapd_max_order;
> -                       classzone_idx = pgdat->classzone_idx;
> +               if (is_node_kswapd(kswapd_p)) {
> +                       new_order = pgdat->kswapd_max_order;
> +                       new_classzone_idx = pgdat->classzone_idx;
>                        pgdat->kswapd_max_order = 0;
>                        pgdat->classzone_idx = MAX_NR_ZONES - 1;
> -               }
> +                       if (order < new_order ||
> +                                       classzone_idx > new_classzone_idx) {
> +                               /*
> +                                * Don't sleep if someone wants a larger 'order'
> +                                * allocation or has tigher zone constraints
> +                                */
> +                               order = new_order;
> +                               classzone_idx = new_classzone_idx;
> +                       } else {
> +                               kswapd_try_to_sleep(kswapd_p, order,
> +                                                   classzone_idx);
> +                               order = pgdat->kswapd_max_order;
> +                               classzone_idx = pgdat->classzone_idx;
> +                               pgdat->kswapd_max_order = 0;
> +                               pgdat->classzone_idx = MAX_NR_ZONES - 1;
> +                       }
> +               } else
> +                       kswapd_try_to_sleep(kswapd_p, order, classzone_idx);
>
>                ret = try_to_freeze();
>                if (kthread_should_stop())
> @@ -2703,8 +2733,13 @@ int kswapd(void *p)
>                 * after returning from the refrigerator
>                 */
>                if (!ret) {
> -                       trace_mm_vmscan_kswapd_wake(pgdat->node_id, order);
> -                       order = balance_pgdat(pgdat, order, &classzone_idx);
> +                       if (is_node_kswapd(kswapd_p)) {
> +                               trace_mm_vmscan_kswapd_wake(pgdat->node_id,
> +                                                               order);
> +                               order = balance_pgdat(pgdat, order,
> +                                                       &classzone_idx);
> +                       } else
> +                               balance_mem_cgroup_pgdat(mem, order);
>                }
>        }
>        return 0;
> @@ -2849,30 +2884,53 @@ static int __devinit cpu_callback(struct notifier_block *nfb,
>  * This kswapd start function will be called by init and node-hot-add.
>  * On node-hot-add, kswapd will moved to proper cpus if cpus are hot-added.
>  */
> -int kswapd_run(int nid)
> +int kswapd_run(int nid, struct mem_cgroup *mem)
>  {
> -       pg_data_t *pgdat = NODE_DATA(nid);
>        struct task_struct *kswapd_thr;
> +       pg_data_t *pgdat = NULL;
>        struct kswapd *kswapd_p;
> +       static char name[TASK_COMM_LEN];
> +       int memcg_id;
>        int ret = 0;
>
> -       if (pgdat->kswapd_wait)
> -               return 0;
> +       if (!mem) {
> +               pgdat = NODE_DATA(nid);
> +               if (pgdat->kswapd_wait)
> +                       return ret;
> +       }
>
>        kswapd_p = kzalloc(sizeof(struct kswapd), GFP_KERNEL);
>        if (!kswapd_p)
>                return -ENOMEM;
>
>        init_waitqueue_head(&kswapd_p->kswapd_wait);
> -       pgdat->kswapd_wait = &kswapd_p->kswapd_wait;
> -       kswapd_p->kswapd_pgdat = pgdat;
>
> -       kswapd_thr = kthread_run(kswapd, kswapd_p, "kswapd%d", nid);
> +       if (!mem) {
> +               pgdat->kswapd_wait = &kswapd_p->kswapd_wait;
> +               kswapd_p->kswapd_pgdat = pgdat;
> +               snprintf(name, TASK_COMM_LEN, "kswapd_%d", nid);
> +       } else {
> +               memcg_id = mem_cgroup_init_kswapd(mem, kswapd_p);
> +               if (!memcg_id) {
> +                       kfree(kswapd_p);
> +                       return ret;
> +               }
> +               snprintf(name, TASK_COMM_LEN, "memcg_%d", memcg_id);
> +       }
> +
> +       kswapd_thr = kthread_run(kswapd, kswapd_p, name);
>        if (IS_ERR(kswapd_thr)) {
>                /* failure at boot is fatal */
>                BUG_ON(system_state == SYSTEM_BOOTING);
> -               printk("Failed to start kswapd on node %d\n",nid);
> -               pgdat->kswapd_wait = NULL;
> +               if (!mem) {
> +                       printk(KERN_ERR "Failed to start kswapd on node %d\n",
> +                                                               nid);
> +                       pgdat->kswapd_wait = NULL;
> +               } else {
> +                       printk(KERN_ERR "Failed to start kswapd on memcg %d\n",
> +                                                               memcg_id);
> +                       mem_cgroup_clear_kswapd(mem);
> +               }
>                kfree(kswapd_p);
>                ret = -1;
>        } else
> @@ -2883,15 +2941,17 @@ int kswapd_run(int nid)
>  /*
>  * Called by memory hotplug when all memory in a node is offlined.
>  */
> -void kswapd_stop(int nid)
> +void kswapd_stop(int nid, struct mem_cgroup *mem)
>  {
>        struct task_struct *kswapd_thr = NULL;
>        struct kswapd *kswapd_p = NULL;
>        wait_queue_head_t *wait;
>
> -       pg_data_t *pgdat = NODE_DATA(nid);
> +       if (!mem)
> +               wait = NODE_DATA(nid)->kswapd_wait;
> +       else
> +               wait = mem_cgroup_kswapd_wait(mem);
>
> -       wait = pgdat->kswapd_wait;
>        if (wait) {
>                kswapd_p = container_of(wait, struct kswapd, kswapd_wait);
>                kswapd_thr = kswapd_p->kswapd_task;
> @@ -2910,7 +2970,7 @@ static int __init kswapd_init(void)
>
>        swap_setup();
>        for_each_node_state(nid, N_HIGH_MEMORY)
> -               kswapd_run(nid);
> +               kswapd_run(nid, NULL);
>        hotcpu_notifier(cpu_callback, 0);
>        return 0;
>  }
> --
> 1.7.3.1
>
>

Let me ask a question.

What's the effect of kswapd_try_to_sleep in memcg?

As I look code, sleeping_prematurely always return false in case of
memcg. So kswapd_try_to_sleep can sleep short time and then sleep
until next wakeup. It means it doesn't have any related to
kswapd_try_to_sleep's goal. So I hope you remove hack of memcg in
kswapd_try_to_sleep and just calling schedule in kswapd function for
sleeping memcg_kswapd.
But I don't look at further patches in series so I may miss something.

-- 
Kind regards,
Minchan Kim
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