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Subject[PATCH v12 11/14] mm: multi-gen LRU: thrashing prevention
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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 [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/20101028191523.GA14972@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>
---
include/linux/mmzone.h | 2 ++
mm/vmscan.c | 71 +++++++++++++++++++++++++++++++++++++++---
2 files changed, 69 insertions(+), 4 deletions(-)

diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index 840b7ca8b91f..472bd5335517 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -419,6 +419,8 @@ 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, lazily sorted on eviction */
struct list_head lists[MAX_NR_GENS][ANON_AND_FILE][MAX_NR_ZONES];
/* the multi-gen LRU sizes, eventually consistent */
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 2b6de7e38aa7..075525a9526a 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -4231,6 +4231,7 @@ static void inc_max_seq(struct lruvec *lruvec, bool can_swap)
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);

@@ -4357,7 +4358,7 @@ static unsigned long get_nr_evictable(struct lruvec *lruvec, unsigned long max_s
return total;
}

-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;
unsigned long nr_to_scan;
@@ -4371,21 +4372,40 @@ static void age_lruvec(struct lruvec *lruvec, struct scan_control *sc)
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 >>= mem_cgroup_online(memcg) ? sc->priority : 0;

+ 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;
+
+ /* the size is likely too small to be helpful */
+ if (!nr_to_scan && sc->priority != DEF_PRIORITY)
+ return false;
+ }
+
if (nr_to_scan && need_aging)
try_to_inc_max_seq(lruvec, max_seq, sc, swappiness);
+
+ 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_WARN_ON_ONCE(!current_is_kswapd());

@@ -4411,12 +4431,28 @@ 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)));

clear_mm_walk();
+
+ /*
+ * 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 && !sc->order && mutex_trylock(&oom_lock)) {
+ struct oom_control oc = {
+ .gfp_mask = sc->gfp_mask,
+ };
+
+ out_of_memory(&oc);
+
+ mutex_unlock(&oom_lock);
+ }
}

/*
@@ -5128,6 +5164,28 @@ static void lru_gen_change_state(bool enabled)
* 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_enabled(struct kobject *kobj, struct kobj_attribute *attr, char *buf)
{
unsigned int caps = 0;
@@ -5176,6 +5234,7 @@ 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
};
@@ -5191,12 +5250,16 @@ 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]);

--
2.36.1.476.g0c4daa206d-goog
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