mm/damon/core: avoid holes in newly set monitoring target ranges

When there are two or more non-contiguous regions intersecting with given
new ranges, 'damon_set_regions()' does not fill the holes.  This commit
makes the function to fill the holes with newly created regions.

[sj@kernel.org: handle error from 'damon_fill_regions_holes()']
  Link: https://lkml.kernel.org/r/20220913215420.57761-1-sj@kernel.org
Link: https://lkml.kernel.org/r/20220909202901.57977-3-sj@kernel.org
Fixes: 3f49584b ("mm/damon: implement primitives for the virtual memory address spaces")
Signed-off-by: SeongJae Park <sj@kernel.org>
Reported-by: Yun Levi <ppbuk5246@gmail.com>
Cc: Brendan Higgins <brendanhiggins@google.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Shuah Khan <shuah@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm/damon/core.c

@@ -168,6 +168,30 @@ static bool damon_intersect(struct damon_region *r,
 	return !(r->ar.end <= re->start || re->end <= r->ar.start);
 }
 
+/*
+ * Fill holes in regions with new regions.
+ */
+static int damon_fill_regions_holes(struct damon_region *first,
+		struct damon_region *last, struct damon_target *t)
+{
+	struct damon_region *r = first;
+
+	damon_for_each_region_from(r, t) {
+		struct damon_region *next, *newr;
+
+		if (r == last)
+			break;
+		next = damon_next_region(r);
+		if (r->ar.end != next->ar.start) {
+			newr = damon_new_region(r->ar.end, next->ar.start);
+			if (!newr)
+				return -ENOMEM;
+			damon_insert_region(newr, r, next, t);
+		}
+	}
+	return 0;
+}
+
 /*
  * damon_set_regions() - Set regions of a target for given address ranges.
  * @t:		the given target.
@@ -184,6 +208,7 @@ int damon_set_regions(struct damon_target *t, struct damon_addr_range *ranges,
 {
 	struct damon_region *r, *next;
 	unsigned int i;
+	int err;
 
 	/* Remove regions which are not in the new ranges */
 	damon_for_each_region_safe(r, next, t) {
@@ -226,6 +251,11 @@ int damon_set_regions(struct damon_target *t, struct damon_addr_range *ranges,
 			first->ar.start = ALIGN_DOWN(range->start,
 					DAMON_MIN_REGION);
 			last->ar.end = ALIGN(range->end, DAMON_MIN_REGION);
+
+			/* fill possible holes in the range */
+			err = damon_fill_regions_holes(first, last, t);
+			if (err)
+				return err;
 		}
 	}
 	return 0;