[patch 240/262] mm/damon/schemes: implement size quota for schemes application speed control

Andrew Morton
2021-11-05T20:47:20Z

From: SeongJae Park <sj@kernel.org>
Subject: mm/damon/schemes: implement size quota for schemes application speed control

There could be arbitrarily large memory regions fulfilling the target data
access pattern of a DAMON-based operation scheme. In the case, applying
the action of the scheme could incur too high overhead. To provide an
intuitive way for avoiding it, this commit implements a feature called
size quota. If the quota is set, DAMON tries to apply the action only up
to the given amount of memory regions within a given time window.

Link: https://lkml.kernel.org/r/20211019150731.16699-3-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 | 36 +++++++++++++++++++++---
mm/damon/core.c | 60 ++++++++++++++++++++++++++++++++++------
mm/damon/dbgfs.c | 4 ++
3 files changed, 87 insertions(+), 13 deletions(-)

--- a/include/linux/damon.h~mm-damon-schemes-implement-size-quota-for-schemes-application-speed-control
+++ a/include/linux/damon.h
@@ -90,6 +90,26 @@ enum damos_action {
};

/**
+ * struct damos_quota - Controls the aggressiveness of the given scheme.
+ * @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_quota {
+ unsigned long sz;
+ unsigned long reset_interval;
+
+/* private: For charging the quota */
+ unsigned long charged_sz;
+ unsigned long charged_from;
+};
+
+/**
* struct damos - Represents a Data Access Monitoring-based Operation Scheme.
* @min_sz_region: Minimum size of target regions.
* @max_sz_region: Maximum size of target regions.
@@ -98,13 +118,20 @@ enum damos_action {
* @min_age_region: Minimum age of target regions.
* @max_age_region: Maximum age of target regions.
* @action: &damo_action to be applied to the target regions.
+ * @quota: Control the aggressiveness of this scheme.
* @stat_count: Total number of regions that this scheme is applied.
* @stat_sz: Total size of regions that this scheme is applied.
* @list: List head for siblings.
*
- * For each aggregation interval, DAMON applies @action to monitoring target
- * regions fit in the condition and updates the statistics. Note that both
- * the minimums and the maximums are inclusive.
+ * For each aggregation interval, DAMON finds regions which fit in the
+ * condition (&min_sz_region, &max_sz_region, &min_nr_accesses,
+ * &max_nr_accesses, &min_age_region, &max_age_region) and applies &action to
+ * those. To avoid consuming too much CPU time or IO resources for the
+ * &action, &quota is used.
+ *
+ * After applying the &action to each region, &stat_count and &stat_sz is
+ * updated to reflect the number of regions and total size of regions that the
+ * &action is applied.
*/
struct damos {
unsigned long min_sz_region;
@@ -114,6 +141,7 @@ struct damos {
unsigned int min_age_region;
unsigned int max_age_region;
enum damos_action action;
+ struct damos_quota quota;
unsigned long stat_count;
unsigned long stat_sz;
struct list_head list;
@@ -310,7 +338,7 @@ struct damos *damon_new_scheme(
unsigned long min_sz_region, unsigned long max_sz_region,
unsigned int min_nr_accesses, unsigned int max_nr_accesses,
unsigned int min_age_region, unsigned int max_age_region,
- enum damos_action action);
+ enum damos_action action, struct damos_quota *quota);
void damon_add_scheme(struct damon_ctx *ctx, struct damos *s);
void damon_destroy_scheme(struct damos *s);

--- a/mm/damon/core.c~mm-damon-schemes-implement-size-quota-for-schemes-application-speed-control
+++ a/mm/damon/core.c
@@ -89,7 +89,7 @@ struct damos *damon_new_scheme(
unsigned long min_sz_region, unsigned long max_sz_region,
unsigned int min_nr_accesses, unsigned int max_nr_accesses,
unsigned int min_age_region, unsigned int max_age_region,
- enum damos_action action)
+ enum damos_action action, struct damos_quota *quota)
{
struct damos *scheme;

@@ -107,6 +107,11 @@ struct damos *damon_new_scheme(
scheme->stat_sz = 0;
INIT_LIST_HEAD(&scheme->list);

+ scheme->quota.sz = quota->sz;
+ scheme->quota.reset_interval = quota->reset_interval;
+ scheme->quota.charged_sz = 0;
+ scheme->quota.charged_from = 0;
+
return scheme;
}

@@ -530,15 +535,25 @@ static void kdamond_reset_aggregated(str
}
}

+static void damon_split_region_at(struct damon_ctx *ctx,
+ struct damon_target *t, struct damon_region *r,
+ unsigned long sz_r);
+
static void damon_do_apply_schemes(struct damon_ctx *c,
struct damon_target *t,
struct damon_region *r)
{
struct damos *s;
- unsigned long sz;

damon_for_each_scheme(s, c) {
- sz = r->ar.end - r->ar.start;
+ struct damos_quota *quota = &s->quota;
+ unsigned long sz = r->ar.end - r->ar.start;
+
+ /* Check the quota */
+ if (quota->sz && quota->charged_sz >= quota->sz)
+ continue;
+
+ /* Check the target regions condition */
if (sz < s->min_sz_region || s->max_sz_region < sz)
continue;
if (r->nr_accesses < s->min_nr_accesses ||
@@ -546,22 +561,51 @@ static void damon_do_apply_schemes(struc
continue;
if (r->age < s->min_age_region || s->max_age_region < r->age)
continue;
- s->stat_count++;
- s->stat_sz += sz;
- if (c->primitive.apply_scheme)
+
+ /* 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,
+ DAMON_MIN_REGION);
+ if (!sz)
+ goto update_stat;
+ damon_split_region_at(c, t, r, sz);
+ }
c->primitive.apply_scheme(c, t, r, s);
+ quota->charged_sz += sz;
+ }
if (s->action != DAMOS_STAT)
r->age = 0;
+
+update_stat:
+ s->stat_count++;
+ s->stat_sz += sz;
}
}

static void kdamond_apply_schemes(struct damon_ctx *c)
{
struct damon_target *t;
- struct damon_region *r;
+ struct damon_region *r, *next_r;
+ struct damos *s;
+
+ damon_for_each_scheme(s, c) {
+ struct damos_quota *quota = &s->quota;
+
+ if (!quota->sz)
+ continue;
+
+ /* New charge window starts */
+ if (time_after_eq(jiffies, quota->charged_from +
+ msecs_to_jiffies(
+ quota->reset_interval))) {
+ quota->charged_from = jiffies;
+ quota->charged_sz = 0;
+ }
+ }

damon_for_each_target(t, c) {
- damon_for_each_region(r, t)
+ damon_for_each_region_safe(r, next_r, t)
damon_do_apply_schemes(c, t, r);
}
}
--- a/mm/damon/dbgfs.c~mm-damon-schemes-implement-size-quota-for-schemes-application-speed-control
+++ a/mm/damon/dbgfs.c
@@ -188,6 +188,8 @@ static struct damos **str_to_schemes(con

*nr_schemes = 0;
while (pos < len && *nr_schemes < max_nr_schemes) {
+ struct damos_quota quota = {};
+
ret = sscanf(&str[pos], "%lu %lu %u %u %u %u %u%n",
&min_sz, &max_sz, &min_nr_a, &max_nr_a,
&min_age, &max_age, &action, &parsed);
@@ -200,7 +202,7 @@ static struct damos **str_to_schemes(con

pos += parsed;
scheme = damon_new_scheme(min_sz, max_sz, min_nr_a, max_nr_a,
- min_age, max_age, action);
+ min_age, max_age, action, &quota);
if (!scheme)
goto fail;

_