mm/damon/core: split out DAMOS-charged region skip logic into a new function

Patch series "mm/damon: cleanup and refactoring code", v2.

This patchset cleans up and refactors a range of DAMON code including the
core, DAMON sysfs interface, and DAMON modules, for better readability and
convenient future feature implementations.

In detail, this patchset splits unnecessarily long and complex functions
in core into smaller functions (patches 1-4).  Then, it cleans up the
DAMON sysfs interface by using more type-safe code (patch 5) and removing
unnecessary function parameters (patch 6).  Further, it refactor the code
by distributing the code into multiple files (patches 7-10).  Last two
patches (patches 11 and 12) deduplicates and remove unnecessary header
inclusion in DAMON modules (reclaim and lru_sort).


This patch (of 12):

The DAMOS action applying function, 'damon_do_apply_schemes()', is quite
long and not so simple.  Split out the already quota-charged region skip
code, which is not a small amount of simple code, into a new function with
some comments for better readability.

Link: https://lkml.kernel.org/r/20221026225943.100429-1-sj@kernel.org
Link: https://lkml.kernel.org/r/20221026225943.100429-2-sj@kernel.orgSigned-off-by: SeongJae Park <sj@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm/damon/core.c

@@ -694,60 +694,94 @@ static bool damos_valid_target(struct damon_ctx *c, struct damon_target *t,
 	return c->ops.get_scheme_score(c, t, r, s) >= s->quota.min_score;
 }
 
-static void damon_do_apply_schemes(struct damon_ctx *c,
-				   struct damon_target *t,
-				   struct damon_region *r)
+/*
+ * damos_skip_charged_region() - Check if the given region or starting part of
+ * it is already charged for the DAMOS quota.
+ * @t:	The target of the region.
+ * @rp:	The pointer to the region.
+ * @s:	The scheme to be applied.
+ *
+ * If a quota of a scheme has exceeded in a quota charge window, the scheme's
+ * action would applied to only a part of the target access pattern fulfilling
+ * regions.  To avoid applying the scheme action to only already applied
+ * regions, DAMON skips applying the scheme action to the regions that charged
+ * in the previous charge window.
+ *
+ * This function checks if a given region should be skipped or not for the
+ * reason.  If only the starting part of the region has previously charged,
+ * this function splits the region into two so that the second one covers the
+ * area that not charged in the previous charge widnow and saves the second
+ * region in *rp and returns false, so that the caller can apply DAMON action
+ * to the second one.
+ *
+ * Return: true if the region should be entirely skipped, false otherwise.
+ */
+static bool damos_skip_charged_region(struct damon_target *t,
+		struct damon_region **rp, struct damos *s)
 {
-	struct damos *s;
-
-	damon_for_each_scheme(s, c) {
+	struct damon_region *r = *rp;
 	struct damos_quota *quota = &s->quota;
-		unsigned long sz = damon_sz_region(r);
-		struct timespec64 begin, end;
-		unsigned long sz_applied = 0;
-
-		if (!s->wmarks.activated)
-			continue;
-
-		/* Check the quota */
-		if (quota->esz && quota->charged_sz >= quota->esz)
-			continue;
+	unsigned long sz_to_skip;
 
 	/* Skip previously charged regions */
 	if (quota->charge_target_from) {
 		if (t != quota->charge_target_from)
-				continue;
+			return true;
 		if (r == damon_last_region(t)) {
 			quota->charge_target_from = NULL;
 			quota->charge_addr_from = 0;
-				continue;
+			return true;
 		}
 		if (quota->charge_addr_from &&
 				r->ar.end <= quota->charge_addr_from)
-				continue;
+			return true;
 
 		if (quota->charge_addr_from && r->ar.start <
 				quota->charge_addr_from) {
-				sz = ALIGN_DOWN(quota->charge_addr_from -
+			sz_to_skip = ALIGN_DOWN(quota->charge_addr_from -
 					r->ar.start, DAMON_MIN_REGION);
-				if (!sz) {
-					if (damon_sz_region(r) <=
-					    DAMON_MIN_REGION)
-						continue;
-					sz = DAMON_MIN_REGION;
+			if (!sz_to_skip) {
+				if (damon_sz_region(r) <= DAMON_MIN_REGION)
+					return true;
+				sz_to_skip = DAMON_MIN_REGION;
 			}
-				damon_split_region_at(t, r, sz);
+			damon_split_region_at(t, r, sz_to_skip);
 			r = damon_next_region(r);
-				sz = damon_sz_region(r);
+			*rp = r;
 		}
 		quota->charge_target_from = NULL;
 		quota->charge_addr_from = 0;
 	}
+	return false;
+}
+
+static void damon_do_apply_schemes(struct damon_ctx *c,
+				   struct damon_target *t,
+				   struct damon_region *r)
+{
+	struct damos *s;
+
+	damon_for_each_scheme(s, c) {
+		struct damos_quota *quota = &s->quota;
+		unsigned long sz;
+		struct timespec64 begin, end;
+		unsigned long sz_applied = 0;
+
+		if (!s->wmarks.activated)
+			continue;
+
+		/* Check the quota */
+		if (quota->esz && quota->charged_sz >= quota->esz)
+			continue;
+
+		if (damos_skip_charged_region(t, &r, s))
+			continue;
 
 		if (!damos_valid_target(c, t, r, s))
 			continue;
 
 		/* Apply the scheme */
+		sz = damon_sz_region(r);
 		if (c->ops.apply_scheme) {
 			if (quota->esz &&
 					quota->charged_sz + sz > quota->esz) {