[patch 242/262] mm/damon/schemes: implement time quota

Andrew Morton
2021-11-05T20:47:28Z

From: SeongJae Park <sj@kernel.org>
Subject: mm/damon/schemes: implement time quota

The size quota feature of DAMOS is useful for IO resource-critical
systems, but not so intuitive for CPU time-critical systems. Systems
using zram or zswap-like swap device would be examples.

To provide another intuitive ways for such systems, this commit implements
time-based quota for DAMON-based Operation Schemes. If the quota is set,
DAMOS tries to use only up to the user-defined quota of CPU time within a
given time window.

Link: https://lkml.kernel.org/r/20211019150731.16699-5-sj@kernel.org
Signed-off-by: SeongJae Park <sj@kernel.org>
Cc: Amit Shah <amit@kernel.org>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: David Hildenbrand <david@redhat.com>
Cc: David Rientjes <rientjes@google.com>
Cc: David Woodhouse <dwmw@amazon.com>
Cc: Greg Thelen <gthelen@google.com>
Cc: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Leonard Foerster <foersleo@amazon.de>
Cc: Marco Elver <elver@google.com>
Cc: Markus Boehme <markubo@amazon.de>
Cc: Shakeel Butt <shakeelb@google.com>
Cc: Shuah Khan <shuah@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

include/linux/damon.h | 25 +++++++++++++++++-----
mm/damon/core.c | 45 +++++++++++++++++++++++++++++++++++-----
2 files changed, 60 insertions(+), 10 deletions(-)

--- a/include/linux/damon.h~mm-damon-schemes-implement-time-quota
+++ a/include/linux/damon.h
@@ -91,20 +91,35 @@ enum damos_action {

/**
* struct damos_quota - Controls the aggressiveness of the given scheme.
+ * @ms: Maximum milliseconds that the scheme can use.
* @sz: Maximum bytes of memory that the action can be applied.
* @reset_interval: Charge reset interval in milliseconds.
*
* To avoid consuming too much CPU time or IO resources for applying the
- * &struct damos->action to large memory, DAMON allows users to set a size
- * quota. The quota can be set by writing non-zero values to &sz. If the size
- * quota is set, DAMON tries to apply the action only up to &sz bytes within
- * &reset_interval.
+ * &struct damos->action to large memory, DAMON allows users to set time and/or
+ * size quotas. The quotas can be set by writing non-zero values to &ms and
+ * &sz, respectively. If the time quota is set, DAMON tries to use only up to
+ * &ms milliseconds within &reset_interval for applying the action. If the
+ * size quota is set, DAMON tries to apply the action only up to &sz bytes
+ * within &reset_interval.
+ *
+ * Internally, the time quota is transformed to a size quota using estimated
+ * throughput of the scheme's action. DAMON then compares it against &sz and
+ * uses smaller one as the effective quota.
*/
struct damos_quota {
+ unsigned long ms;
unsigned long sz;
unsigned long reset_interval;

-/* private: For charging the quota */
+/* private: */
+ /* For throughput estimation */
+ unsigned long total_charged_sz;
+ unsigned long total_charged_ns;
+
+ unsigned long esz; /* Effective size quota in bytes */
+
+ /* For charging the quota */
unsigned long charged_sz;
unsigned long charged_from;
struct damon_target *charge_target_from;
--- a/mm/damon/core.c~mm-damon-schemes-implement-time-quota
+++ a/mm/damon/core.c
@@ -107,8 +107,12 @@ struct damos *damon_new_scheme(
scheme->stat_sz = 0;
INIT_LIST_HEAD(&scheme->list);

+ scheme->quota.ms = quota->ms;
scheme->quota.sz = quota->sz;
scheme->quota.reset_interval = quota->reset_interval;
+ scheme->quota.total_charged_sz = 0;
+ scheme->quota.total_charged_ns = 0;
+ scheme->quota.esz = 0;
scheme->quota.charged_sz = 0;
scheme->quota.charged_from = 0;
scheme->quota.charge_target_from = NULL;
@@ -550,9 +554,10 @@ static void damon_do_apply_schemes(struc
damon_for_each_scheme(s, c) {
struct damos_quota *quota = &s->quota;
unsigned long sz = r->ar.end - r->ar.start;
+ struct timespec64 begin, end;

/* Check the quota */
- if (quota->sz && quota->charged_sz >= quota->sz)
+ if (quota->esz && quota->charged_sz >= quota->esz)
continue;

/* Skip previously charged regions */
@@ -597,16 +602,21 @@ static void damon_do_apply_schemes(struc

/* Apply the scheme */
if (c->primitive.apply_scheme) {
- if (quota->sz && quota->charged_sz + sz > quota->sz) {
- sz = ALIGN_DOWN(quota->sz - quota->charged_sz,
+ if (quota->esz &&
+ quota->charged_sz + sz > quota->esz) {
+ sz = ALIGN_DOWN(quota->esz - quota->charged_sz,
DAMON_MIN_REGION);
if (!sz)
goto update_stat;
damon_split_region_at(c, t, r, sz);
}
+ ktime_get_coarse_ts64(&begin);
c->primitive.apply_scheme(c, t, r, s);
+ ktime_get_coarse_ts64(&end);
+ quota->total_charged_ns += timespec64_to_ns(&end) -
+ timespec64_to_ns(&begin);
quota->charged_sz += sz;
- if (quota->sz && quota->charged_sz >= quota->sz) {
+ if (quota->esz && quota->charged_sz >= quota->esz) {
quota->charge_target_from = t;
quota->charge_addr_from = r->ar.end + 1;
}
@@ -620,6 +630,29 @@ update_stat:
}
}

+/* Shouldn't be called if quota->ms and quota->sz are zero */
+static void damos_set_effective_quota(struct damos_quota *quota)
+{
+ unsigned long throughput;
+ unsigned long esz;
+
+ if (!quota->ms) {
+ quota->esz = quota->sz;
+ return;
+ }
+
+ if (quota->total_charged_ns)
+ throughput = quota->total_charged_sz * 1000000 /
+ quota->total_charged_ns;
+ else
+ throughput = PAGE_SIZE * 1024;
+ esz = throughput * quota->ms;
+
+ if (quota->sz && quota->sz < esz)
+ esz = quota->sz;
+ quota->esz = esz;
+}
+
static void kdamond_apply_schemes(struct damon_ctx *c)
{
struct damon_target *t;
@@ -629,15 +662,17 @@ static void kdamond_apply_schemes(struct
damon_for_each_scheme(s, c) {
struct damos_quota *quota = &s->quota;

- if (!quota->sz)
+ if (!quota->ms && !quota->sz)
continue;

/* New charge window starts */
if (time_after_eq(jiffies, quota->charged_from +
msecs_to_jiffies(
quota->reset_interval))) {
+ quota->total_charged_sz += quota->charged_sz;
quota->charged_from = jiffies;
quota->charged_sz = 0;
+ damos_set_effective_quota(quota);
}
}

_