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From:   xiakaixu1987@gmail.com
To:     sj@kernel.org, akpm@linux-foundation.org
Cc:     damon@lists.linux.dev, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org, Kaixu Xia <kaixuxia@tencent.com>
Subject: [PATCH v2 2/2] mm/damon/vaddr: remove comparison between mm and last_mm when checking region accesses
Date:   Sat, 27 Aug 2022 17:02:51 +0800
Message-Id: <1661590971-20893-3-git-send-email-kaixuxia@tencent.com>
In-Reply-To: <1661590971-20893-1-git-send-email-kaixuxia@tencent.com>
References: <1661590971-20893-1-git-send-email-kaixuxia@tencent.com>
Precedence: bulk

From: Kaixu Xia <kaixuxia@tencent.com>

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.

Signed-off-by: Kaixu Xia <kaixuxia@tencent.com>
---
 mm/damon/vaddr.c | 11 ++++++-----
 1 file changed, 6 insertions(+), 5 deletions(-)

diff --git a/mm/damon/vaddr.c b/mm/damon/vaddr.c
index e481f81c3efb..5f66c826ee3a 100644
--- a/mm/damon/vaddr.c
+++ b/mm/damon/vaddr.c
@@ -533,15 +533,14 @@ 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++;
@@ -552,7 +551,6 @@ static void __damon_va_check_access(struct mm_struct *mm,
 	if (last_accessed)
 		r->nr_accesses++;
 
-	last_mm = mm;
 	last_addr = r->sampling_addr;
 }
 
@@ -562,14 +560,17 @@ 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);
 	}
-- 
2.27.0