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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,
	stable@vger.kernel.org,
	linux-kernel@vger.kernel.org
Subject: [PATCH 1/2] mm/damon/reclaim: fix quota stauts loss due to online tunings
Date: Fri, 16 Feb 2024 11:40:24 -0800
Message-Id: <20240216194025.9207-2-sj@kernel.org>
In-Reply-To: <20240216194025.9207-1-sj@kernel.org>
References: <20240216194025.9207-1-sj@kernel.org>
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For online parameters change, DAMON_RECLAIM creates new scheme based on
latest values of the parameters and replaces the old scheme with the new
one.  When creating it, the internal status of the quota of the old
scheme is not preserved.  As a result, charging of the quota starts from
zero after the online tuning.  The data that collected to estimate the
throughput of the scheme's action is also reset, and therefore the
estimation should start from the scratch again.  Because the throughput
estimation is being used to convert the time quota to the effective size
quota, this could result in temporal time quota inaccuracy.  It would be
recovered over time, though.  In short, the quota accuracy could be
temporarily degraded after online parameters update.

Fix the problem by checking the case and copying the internal fields for
the status.

Fixes: e035c280f6df ("mm/damon/reclaim: support online inputs update")
Cc: <stable@vger.kernel.org> # 5.19.x
Signed-off-by: SeongJae Park <sj@kernel.org>
---
 mm/damon/reclaim.c | 18 +++++++++++++++++-
 1 file changed, 17 insertions(+), 1 deletion(-)

diff --git a/mm/damon/reclaim.c b/mm/damon/reclaim.c
index ab974e477d2f..66e190f0374a 100644
--- a/mm/damon/reclaim.c
+++ b/mm/damon/reclaim.c
@@ -150,9 +150,20 @@ static struct damos *damon_reclaim_new_scheme(void)
 			&damon_reclaim_wmarks);
 }
 
+static void damon_reclaim_copy_quota_status(struct damos_quota *dst,
+		struct damos_quota *src)
+{
+	dst->total_charged_sz = src->total_charged_sz;
+	dst->total_charged_ns = src->total_charged_ns;
+	dst->charged_sz = src->charged_sz;
+	dst->charged_from = src->charged_from;
+	dst->charge_target_from = src->charge_target_from;
+	dst->charge_addr_from = src->charge_addr_from;
+}
+
 static int damon_reclaim_apply_parameters(void)
 {
-	struct damos *scheme;
+	struct damos *scheme, *old_scheme;
 	struct damos_filter *filter;
 	int err = 0;
 
@@ -164,6 +175,11 @@ static int damon_reclaim_apply_parameters(void)
 	scheme = damon_reclaim_new_scheme();
 	if (!scheme)
 		return -ENOMEM;
+	if (!list_empty(&ctx->schemes)) {
+		damon_for_each_scheme(old_scheme, ctx)
+			damon_reclaim_copy_quota_status(&scheme->quota,
+					&old_scheme->quota);
+	}
 	if (skip_anon) {
 		filter = damos_new_filter(DAMOS_FILTER_TYPE_ANON, true);
 		if (!filter) {
-- 
2.39.2