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From:   SeongJae Park <sj38.park@gmail.com>
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Subject: [RFC v3 03/15] damon/core/schemes: Skip already charged targets and regions
Date:   Tue, 20 Jul 2021 13:12:57 +0000
Message-Id: <20210720131309.22073-4-sj38.park@gmail.com>
In-Reply-To: <20210720131309.22073-1-sj38.park@gmail.com>
References: <20210720131309.22073-1-sj38.park@gmail.com>
Precedence: bulk

From: SeongJae Park <sjpark@amazon.de>

If DAMOS stopped applying action to memory regions due to the speed
limit, it does nothing until next charge window starts.  Then, it starts
the work from the beginning of the address space.  If there is a huge
memory region at the beginning of the address space and it fulfills the
scheme target data access pattern, the action will applied to only the
region.

This commit mitigates the case by skipping memory regions that charged
in previous charge window at the beginning of current charge window.

Signed-off-by: SeongJae Park <sjpark@amazon.de>
---
 include/linux/damon.h |  5 +++++
 mm/damon/core.c       | 37 +++++++++++++++++++++++++++++++++++++
 2 files changed, 42 insertions(+)

diff --git a/include/linux/damon.h b/include/linux/damon.h
index 9c996adb02b8..7b1fa506e7a6 100644
--- a/include/linux/damon.h
+++ b/include/linux/damon.h
@@ -107,6 +107,8 @@ struct damos_quota {
 /* private: For charging the quota */
 	unsigned long charged_sz;
 	unsigned long charged_from;
+	struct damon_target *charge_target_from;
+	unsigned long charge_addr_from;
 };
 
 /**
@@ -335,6 +337,9 @@ struct damon_ctx {
 #define damon_prev_region(r) \
 	(container_of(r->list.prev, struct damon_region, list))
 
+#define damon_last_region(t) \
+	(list_last_entry(&t->regions_list, struct damon_region, list))
+
 #define damon_for_each_region(r, t) \
 	list_for_each_entry(r, &t->regions_list, list)
 
diff --git a/mm/damon/core.c b/mm/damon/core.c
index 00804a1e5e2a..a41eb9d885bb 100644
--- a/mm/damon/core.c
+++ b/mm/damon/core.c
@@ -111,6 +111,8 @@ struct damos *damon_new_scheme(
 	scheme->quota.reset_interval = quota->reset_interval;
 	scheme->quota.charged_sz = 0;
 	scheme->quota.charged_from = 0;
+	scheme->quota.charge_target_from = NULL;
+	scheme->quota.charge_addr_from = 0;
 
 	return scheme;
 }
@@ -558,6 +560,37 @@ static void damon_do_apply_schemes(struct damon_ctx *c,
 		if (quota->sz && quota->charged_sz >= quota->sz)
 			continue;
 
+		/* Skip previously charged regions */
+		if (quota->charge_target_from) {
+			if (t != quota->charge_target_from)
+				continue;
+			if (r == damon_last_region(t)) {
+				quota->charge_target_from = NULL;
+				quota->charge_addr_from = 0;
+				continue;
+			}
+			if (quota->charge_addr_from &&
+					r->ar.end <= quota->charge_addr_from)
+				continue;
+
+			if (quota->charge_addr_from && r->ar.start <
+					quota->charge_addr_from) {
+				sz = ALIGN_DOWN(quota->charge_addr_from -
+						r->ar.start, DAMON_MIN_REGION);
+				if (!sz) {
+					if (r->ar.end - r->ar.start <=
+							DAMON_MIN_REGION)
+						continue;
+					sz = DAMON_MIN_REGION;
+				}
+				damon_split_region_at(c, t, r, sz);
+				r = damon_next_region(r);
+				sz = r->ar.end - r->ar.start;
+			}
+			quota->charge_target_from = NULL;
+			quota->charge_addr_from = 0;
+		}
+
 		/* Check the target regions condition */
 		if (sz < s->min_sz_region || s->max_sz_region < sz)
 			continue;
@@ -578,6 +611,10 @@ static void damon_do_apply_schemes(struct damon_ctx *c,
 			}
 			c->primitive.apply_scheme(c, t, r, s);
 			quota->charged_sz += sz;
+			if (quota->sz && quota->charged_sz >= quota->sz) {
+				quota->charge_target_from = t;
+				quota->charge_addr_from = r->ar.end + 1;
+			}
 		}
 		if (s->action != DAMOS_STAT)
 			r->age = 0;
-- 
2.17.1