Re: [PATCH v9 11/14] mm: multi-gen LRU: thrashing prevention

[Barry Song <21cnbao@gmail.com>]

On Wed, Mar 9, 2022 at 3:48 PM Yu Zhao <yuzhao@google.com> wrote:
>
> Add /sys/kernel/mm/lru_gen/min_ttl_ms for thrashing prevention, as
> requested by many desktop users [1].
>
> When set to value N, it prevents the working set of N milliseconds
> from getting evicted. The OOM killer is triggered if this working set
> cannot be kept in memory. Based on the average human detectable lag
> (~100ms), N=1000 usually eliminates intolerable lags due to thrashing.
> Larger values like N=3000 make lags less noticeable at the risk of
> premature OOM kills.
>
> Compared with the size-based approach, e.g., [2], this time-based
> approach has the following advantages:
> 1. It is easier to configure because it is agnostic to applications
>    and memory sizes.
> 2. It is more reliable because it is directly wired to the OOM killer.
>

how are userspace oom daemons like android lmkd, systemd-oomd supposed
to work with this time-based oom killer?
only one of min_ttl_ms and userspace daemon should be enabled? or both
should be enabled at the same time?

> [1] https://lore.kernel.org/lkml/Ydza%2FzXKY9ATRoh6@google.com/
> [2] https://lore.kernel.org/lkml/20211130201652.2218636d@mail.inbox.lv/
>
> Signed-off-by: Yu Zhao <yuzhao@google.com>
> Acked-by: Brian Geffon <bgeffon@google.com>
> Acked-by: Jan Alexander Steffens (heftig) <heftig@archlinux.org>
> Acked-by: Oleksandr Natalenko <oleksandr@natalenko.name>
> Acked-by: Steven Barrett <steven@liquorix.net>
> Acked-by: Suleiman Souhlal <suleiman@google.com>
> Tested-by: Daniel Byrne <djbyrne@mtu.edu>
> Tested-by: Donald Carr <d@chaos-reins.com>
> Tested-by: Holger Hoffstätte <holger@applied-asynchrony.com>
> Tested-by: Konstantin Kharlamov <Hi-Angel@yandex.ru>
> Tested-by: Shuang Zhai <szhai2@cs.rochester.edu>
> Tested-by: Sofia Trinh <sofia.trinh@edi.works>
> Tested-by: Vaibhav Jain <vaibhav@linux.ibm.com>
> ---
>  include/linux/mmzone.h |  2 ++
>  mm/vmscan.c            | 69 +++++++++++++++++++++++++++++++++++++++---
>  2 files changed, 67 insertions(+), 4 deletions(-)
>
> diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
> index 116c9237e401..f98f9ce50e67 100644
> --- a/include/linux/mmzone.h
> +++ b/include/linux/mmzone.h
> @@ -403,6 +403,8 @@ struct lru_gen_struct {
>         unsigned long max_seq;
>         /* the eviction increments the oldest generation numbers */
>         unsigned long min_seq[ANON_AND_FILE];
> +       /* the birth time of each generation in jiffies */
> +       unsigned long timestamps[MAX_NR_GENS];
>         /* the multi-gen LRU lists */
>         struct list_head lists[MAX_NR_GENS][ANON_AND_FILE][MAX_NR_ZONES];
>         /* the sizes of the above lists */
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index 55cc7d6b018b..6aa083b8bb26 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -4229,6 +4229,7 @@ static void inc_max_seq(struct lruvec *lruvec)
>         for (type = 0; type < ANON_AND_FILE; type++)
>                 reset_ctrl_pos(lruvec, type, false);
>
> +       WRITE_ONCE(lrugen->timestamps[next], jiffies);
>         /* make sure preceding modifications appear */
>         smp_store_release(&lrugen->max_seq, lrugen->max_seq + 1);
>
> @@ -4340,7 +4341,8 @@ static long get_nr_evictable(struct lruvec *lruvec, unsigned long max_seq,
>         return total > 0 ? total : 0;
>  }
>
> -static void age_lruvec(struct lruvec *lruvec, struct scan_control *sc)
> +static bool age_lruvec(struct lruvec *lruvec, struct scan_control *sc,
> +                      unsigned long min_ttl)
>  {
>         bool need_aging;
>         long nr_to_scan;
> @@ -4349,14 +4351,22 @@ static void age_lruvec(struct lruvec *lruvec, struct scan_control *sc)
>         DEFINE_MAX_SEQ(lruvec);
>         DEFINE_MIN_SEQ(lruvec);
>
> +       if (min_ttl) {
> +               int gen = lru_gen_from_seq(min_seq[LRU_GEN_FILE]);
> +               unsigned long birth = READ_ONCE(lruvec->lrugen.timestamps[gen]);
> +
> +               if (time_is_after_jiffies(birth + min_ttl))
> +                       return false;
> +       }
> +
>         mem_cgroup_calculate_protection(NULL, memcg);
>
>         if (mem_cgroup_below_min(memcg))
> -               return;
> +               return false;
>
>         nr_to_scan = get_nr_evictable(lruvec, max_seq, min_seq, swappiness, &need_aging);
>         if (!nr_to_scan)
> -               return;
> +               return false;
>
>         nr_to_scan >>= sc->priority;
>
> @@ -4365,11 +4375,18 @@ static void age_lruvec(struct lruvec *lruvec, struct scan_control *sc)
>
>         if (nr_to_scan && need_aging && (!mem_cgroup_below_low(memcg) || sc->memcg_low_reclaim))
>                 try_to_inc_max_seq(lruvec, max_seq, sc, swappiness, false);
> +
> +       return true;
>  }
>
> +/* to protect the working set of the last N jiffies */
> +static unsigned long lru_gen_min_ttl __read_mostly;
> +
>  static void lru_gen_age_node(struct pglist_data *pgdat, struct scan_control *sc)
>  {
>         struct mem_cgroup *memcg;
> +       bool success = false;
> +       unsigned long min_ttl = READ_ONCE(lru_gen_min_ttl);
>
>         VM_BUG_ON(!current_is_kswapd());
>
> @@ -4395,12 +4412,29 @@ static void lru_gen_age_node(struct pglist_data *pgdat, struct scan_control *sc)
>         do {
>                 struct lruvec *lruvec = mem_cgroup_lruvec(memcg, pgdat);
>
> -               age_lruvec(lruvec, sc);
> +               if (age_lruvec(lruvec, sc, min_ttl))
> +                       success = true;
>
>                 cond_resched();
>         } while ((memcg = mem_cgroup_iter(NULL, memcg, NULL)));
>
>         current->reclaim_state->mm_walk = NULL;
> +
> +       /*
> +        * The main goal is to OOM kill if every generation from all memcgs is
> +        * younger than min_ttl. However, another theoretical possibility is all
> +        * memcgs are either below min or empty.
> +        */
> +       if (!success && mutex_trylock(&oom_lock)) {
> +               struct oom_control oc = {
> +                       .gfp_mask = sc->gfp_mask,
> +                       .order = sc->order,
> +               };
> +
> +               out_of_memory(&oc);
> +
> +               mutex_unlock(&oom_lock);
> +       }
>  }
>
>  /*
> @@ -5112,6 +5146,28 @@ static void lru_gen_change_state(bool enable)
>   *                          sysfs interface
>   ******************************************************************************/
>
> +static ssize_t show_min_ttl(struct kobject *kobj, struct kobj_attribute *attr, char *buf)
> +{
> +       return sprintf(buf, "%u\n", jiffies_to_msecs(READ_ONCE(lru_gen_min_ttl)));
> +}
> +
> +static ssize_t store_min_ttl(struct kobject *kobj, struct kobj_attribute *attr,
> +                            const char *buf, size_t len)
> +{
> +       unsigned int msecs;
> +
> +       if (kstrtouint(buf, 0, &msecs))
> +               return -EINVAL;
> +
> +       WRITE_ONCE(lru_gen_min_ttl, msecs_to_jiffies(msecs));
> +
> +       return len;
> +}
> +
> +static struct kobj_attribute lru_gen_min_ttl_attr = __ATTR(
> +       min_ttl_ms, 0644, show_min_ttl, store_min_ttl
> +);
> +
>  static ssize_t show_enable(struct kobject *kobj, struct kobj_attribute *attr, char *buf)
>  {
>         unsigned int caps = 0;
> @@ -5160,6 +5216,7 @@ static struct kobj_attribute lru_gen_enabled_attr = __ATTR(
>  );
>
>  static struct attribute *lru_gen_attrs[] = {
> +       &lru_gen_min_ttl_attr.attr,
>         &lru_gen_enabled_attr.attr,
>         NULL
>  };
> @@ -5175,12 +5232,16 @@ static struct attribute_group lru_gen_attr_group = {
>
>  void lru_gen_init_lruvec(struct lruvec *lruvec)
>  {
> +       int i;
>         int gen, type, zone;
>         struct lru_gen_struct *lrugen = &lruvec->lrugen;
>
>         lrugen->max_seq = MIN_NR_GENS + 1;
>         lrugen->enabled = lru_gen_enabled();
>
> +       for (i = 0; i <= MIN_NR_GENS + 1; i++)
> +               lrugen->timestamps[i] = jiffies;
> +
>         for_each_gen_type_zone(gen, type, zone)
>                 INIT_LIST_HEAD(&lrugen->lists[gen][type][zone]);
>
> --
> 2.35.1.616.g0bdcbb4464-goog
>

Thanks
Barry