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

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