mm: multi-gen LRU: thrashing prevention

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.

[1] https://lore.kernel.org/r/Ydza%2FzXKY9ATRoh6@google.com/
[2] https://lore.kernel.org/r/20211130201652.2218636d@mail.inbox.lv/

Link: https://lkml.kernel.org/r/20220407031525.2368067-12-yuzhao@google.com
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>
Cc: Barry Song <baohua@kernel.org>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Will Deacon <will@kernel.org>
Cc: Yang Shi <shy828301@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index daa31f756be6450638a5e6d994cc2b90404845da..9aaa04ac862f6692c3175a71bb6c1387df275ee0 100644 (file)
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -416,6 +416,8 @@ 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 3908acf6618e42998269961a51db16e7ab8bb2e7..9327b2f63665c903cd77c589a9fda0627f7f9cca 100644 (file)
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -4192,6 +4192,7 @@ 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);
 
@@ -4317,7 +4318,8 @@ 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;
@@ -4326,14 +4328,22 @@ 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;
 
@@ -4342,11 +4352,18 @@ 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());
 
@@ -4372,12 +4389,29 @@ 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);
+       }
 }
 
 /*
@@ -5092,6 +5126,28 @@ unlock:
  *                          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;
@@ -5140,6 +5196,7 @@ 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
 };
@@ -5155,12 +5212,16 @@ 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]);