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From:   SeongJae Park <sj@kernel.org>
To:     Andrew Morton <akpm@linux-foundation.org>
Cc:     SeongJae Park <sj@kernel.org>, damon@lists.linux.dev,
        linux-mm@kvack.org, linux-kernel@vger.kernel.org
Subject: [PATCH 2/8] mm/damon/vaddr: call damon_update_region_access_rate() always
Date:   Fri, 15 Sep 2023 02:52:45 +0000
Message-Id: <20230915025251.72816-3-sj@kernel.org>
In-Reply-To: <20230915025251.72816-1-sj@kernel.org>
References: <20230915025251.72816-1-sj@kernel.org>
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When getting mm_struct of the monitoring target process fails, there wil
be no need to increase the access rate counter (nr_accesses) of the
regions for the process.  Hence, damon_va_check_accesses() skips calling
damon_update_region_access_rate() in the case.  This breaks the
assumption that damon_update_region_access_rate() is called for every
region, for every sampling interval.  Call the function for every region
even in the case.  This might increase the overhead in some cases, but
such case would not be frequent, so no significant impact is really
expected.

Signed-off-by: SeongJae Park <sj@kernel.org>
---
 mm/damon/vaddr.c | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/mm/damon/vaddr.c b/mm/damon/vaddr.c
index 7fc0bda73b4c..e36303271f9d 100644
--- a/mm/damon/vaddr.c
+++ b/mm/damon/vaddr.c
@@ -563,6 +563,11 @@ static void __damon_va_check_access(struct mm_struct *mm,
 	static unsigned long last_folio_sz = PAGE_SIZE;
 	static bool last_accessed;
 
+	if (!mm) {
+		damon_update_region_access_rate(r, false);
+		return;
+	}
+
 	/* If the region is in the last checked page, reuse the result */
 	if (same_target && (ALIGN_DOWN(last_addr, last_folio_sz) ==
 				ALIGN_DOWN(r->sampling_addr, last_folio_sz))) {
@@ -586,15 +591,14 @@ static unsigned int damon_va_check_accesses(struct damon_ctx *ctx)
 
 	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, same_target);
 			max_nr_accesses = max(r->nr_accesses, max_nr_accesses);
 			same_target = true;
 		}
-		mmput(mm);
+		if (mm)
+			mmput(mm);
 	}
 
 	return max_nr_accesses;
-- 
2.25.1