mm/damon/vaddr: remove comparison between mm and last_mm when checking region accesses

The damon regions that belong to the same damon target have the same
'struct mm_struct *mm', so it's unnecessary to compare the mm and last_mm
objects among the damon regions in one damon target when checking
accesses.  But the check is necessary when the target changed in
'__damon_va_check_accesses()', so we can simplify the whole operation by
using the bool 'same_target' to indicate whether the target changed.

Link: https://lkml.kernel.org/r/1661590971-20893-3-git-send-email-kaixuxia@tencent.comSigned-off-by: Kaixu Xia <kaixuxia@tencent.com>
Reviewed-by: SeongJae Park <sj@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm/damon/vaddr.c

@@ -543,15 +543,14 @@ static bool damon_va_young(struct mm_struct *mm, unsigned long addr,
  * r	the region to be checked
  */
 static void __damon_va_check_access(struct mm_struct *mm,
-				struct damon_region *r)
+				struct damon_region *r, bool same_target)
 {
-	static struct mm_struct *last_mm;
 	static unsigned long last_addr;
 	static unsigned long last_page_sz = PAGE_SIZE;
 	static bool last_accessed;
 
 	/* If the region is in the last checked page, reuse the result */
-	if (mm == last_mm && (ALIGN_DOWN(last_addr, last_page_sz) ==
+	if (same_target && (ALIGN_DOWN(last_addr, last_page_sz) ==
 				ALIGN_DOWN(r->sampling_addr, last_page_sz))) {
 		if (last_accessed)
 			r->nr_accesses++;
@@ -562,7 +561,6 @@ static void __damon_va_check_access(struct mm_struct *mm,
 	if (last_accessed)
 		r->nr_accesses++;
 
-	last_mm = mm;
 	last_addr = r->sampling_addr;
 }
 
@@ -572,14 +570,17 @@ static unsigned int damon_va_check_accesses(struct damon_ctx *ctx)
 	struct mm_struct *mm;
 	struct damon_region *r;
 	unsigned int max_nr_accesses = 0;
+	bool same_target;
 
 	damon_for_each_target(t, ctx) {
 		mm = damon_get_mm(t);
 		if (!mm)
 			continue;
+		same_target = false;
 		damon_for_each_region(r, t) {
-			__damon_va_check_access(mm, r);
+			__damon_va_check_access(mm, r, same_target);
 			max_nr_accesses = max(r->nr_accesses, max_nr_accesses);
+			same_target = true;
 		}
 		mmput(mm);
 	}