mm/damon/core: use abs() instead of diff_of()

In kernel, we can use abs(a - b) to get the absolute value, So there is no
need to redefine a new one.

Link: https://lkml.kernel.org/r/b24e7b82d9efa90daf150d62dea171e19390ad0b.1636989871.git.xhao@linux.alibaba.com
Signed-off-by: Xin Hao <xhao@linux.alibaba.com>
Reviewed-by: Muchun Song <songmuchun@bytedance.com>
Reviewed-by: SeongJae Park <sj@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/damon/core.c

@@ -750,8 +750,6 @@ static void damon_merge_two_regions(struct damon_target *t,
 	damon_destroy_region(r, t);
 }
 
-#define diff_of(a, b) (a > b ? a - b : b - a)
-
 /*
  * Merge adjacent regions having similar access frequencies
  *
@@ -765,13 +763,13 @@ static void damon_merge_regions_of(struct damon_target *t, unsigned int thres,
 	struct damon_region *r, *prev = NULL, *next;
 
 	damon_for_each_region_safe(r, next, t) {
-		if (diff_of(r->nr_accesses, r->last_nr_accesses) > thres)
+		if (abs(r->nr_accesses - r->last_nr_accesses) > thres)
 			r->age = 0;
 		else
 			r->age++;
 
 		if (prev && prev->ar.end == r->ar.start &&
-		    diff_of(prev->nr_accesses, r->nr_accesses) <= thres &&
+		    abs(prev->nr_accesses - r->nr_accesses) <= thres &&
 		    sz_damon_region(prev) + sz_damon_region(r) <= sz_limit)
 			damon_merge_two_regions(t, prev, r);
 		else