From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=100.103.45.18 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1794064475; b=u35fpqB2W4RWCSyR1Umebe4j2apOol9ipjTPQn7aD4zabJm0bMKkQZLU4b9bH/E9Yl0K ZQDAY5soTTWS1WsCZ+kIKWxgxfqd7KdrOXgqwBSONRQ9nduo5J+w8vV9Rqxfs6Hw8T5co E2OH37XORdW7uHZNZawaFKw5QZJkcTYAunsAhcDv5iRENQHGtlNhkyx1whetuN4z6SYwq 6lJqCvxHcnpF+hFK4SNWdCKHsz1ugpiA+W1pRE87uyixBky9oKyjIqrud2Xj5Fc/JqGHR k/fjo3MEPQ77U60yjULEPNemJq+dLZIvxfRuPdCTARWYTgPGeqOpie+Hu5XyLA6SZ+A== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1794064475; h=Received:DKIM-Signature:From:To:Cc:Subject:Date:Message-ID:X-Mailer: In-Reply-To:References:User-Agent:X-stable:X-Patchwork-Hint: MIME-Version:Content-Transfer-Encoding; bh=h5cib/+4RYP1T7lH3tl2Vwf9fFE45bm6nTxeIuDG56w=; b=bIXHu9UMDmkvkMJSLfzBBFTac4RDUm1E8CeDTSyJOT8WuIzB4yz2dai2o5GTXZoPxDfO AEAXyxhG08BZz/zP5GqVAlXUC9jgrbWHb9VmdRu3Lf+YlZ+gw13lUBNdpmC4aebc1ab36 wVxQN+N+ZqL7++o1wpneGFUis297ZU6VfAcHZjAwiu3mgNr6P/QCFzcr2R65h9FFqDoQa efVKb02BbaBcaiABn6MPaa7UlmGGGnjtdWiSpKDRaiCT2chlO72GpTwlqdfiWAhbdtyom Vp6oHJBr5NAWCZ8m4liSqkFYZKXX59TKG0uL31dKR0Jq57HFGrROKeIxlLXA/L/fzNA== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass header.d=linuxfoundation.org header.i=@linuxfoundation.org header.a=rsa-sha256 header.s=korg header.b=HKu1rz11; arc=none smtp.remote-ip=100.103.45.18 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (prime256v1)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id BBC07606C015; Sat, 7 Nov 2026 15:14:34 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.a=rsa-sha256 header.s=korg header.b=HKu1rz11 Received: by smtp.kernel.org (Postfix) with ESMTPSA id 689071F008A3; Sat, 7 Nov 2026 15:14:34 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1794064474; bh=h5cib/+4RYP1T7lH3tl2Vwf9fFE45bm6nTxeIuDG56w=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=HKu1rz11gIQgPMzPTWtOxQ8aLQzIl4+h1gnI8PunVQIbmTFk1wH0/sYvI4jlGrn7B /n8LWd/caPZpeAC+K7BS8HZwzkyVJL7UaFmhIV27qZRJNphEFPTRAYXYscPtIz728U 8ghFpYT8hs9H1V4fS4aXs6l6o+DcjyMVrh8484yk= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, SJ Park , Andrew Morton , Lian Wang , Kunwu Chan , Brendan Higgins , David Gow , Quanmin Yan , Sasha Levin Subject: [PATCH 7.3 0514/1257] mm/damon/core: handle uninitialized damos_quota_goal->last_psi_total Date: Sat, 7 Nov 2026 08:46:50 -0500 Message-ID: <20261107134953.630670939@linuxfoundation.org> X-Mailer: git-send-email 2.56.0 In-Reply-To: <20261107134939.434104957@linuxfoundation.org> References: <20261107134939.434104957@linuxfoundation.org> User-Agent: quilt/0.69 X-stable: review X-Patchwork-Hint: ignore X-Mailing-List: stable@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 7.3-stable review patch. If anyone has any objections, please let me know. ------------------ From: SJ Park [ Upstream commit 29c6084658af41b5b1fefd873d26d441830ced34 ] When DAMOS_QUOTA_SOME_MEM_PSI_US metric damos quota goal is set, the PSI delta for the feedback loop is calculated using damos_quota_goal->last_psi_total. However, it is initialized only after the first feedback loop. The first iteration of the loop uses the uninitialized value. As a result, the feedback loop can change the effective quota in an unexpected way at the first iteration. The user impact of the issue is not big, because the issue impacts only the first iteration of the feedback loop. The feedback loop also has an internal cap of the quota adjustment. The wrong adjustment will soon be corrected over a few iterations. For this reason, doing no initialization at commit time was intentional. It is also explicitly commented. That said, nobody likes behaviors that are unexpected or difficult to be expected. Check last_psi_total initialization and skip the tuning round when it is not initialized. For this, initialize last_psi_total with U64_MAX in the goal creation and the goal commit time. U64_MAX means the field is not initialized. The tuning round shows the value and adjusts it to guarantee the current quota is maintained for the round, and last_psi_total is correctly initialized on the next round. Before this change, committing a new PSI goal on an existing PSI goal with goal-only DAMON sysfs command (commit_schemes_quota_goals) just worked. After this change, the tuning round right after the commit will be unnecessarily skipped, because last_psi_total is unconditionally marked as not initialized in the damos_commit_quota_goal_union(). This is an intended tradeoff for simplicity. Skipping just one round of tuning is no problem. Meanwhile it makes both the code and the behavior simple to understand. Also update the quota goal commit unit test for changed last_psi_total setup behavior. The issue was discovered [1] by Sashiko. Link: https://lore.kernel.org/20260902002725.108635-3-sj@kernel.org Link: https://lore.kernel.org/20260718005316.89585-1-sj@kernel.org [1] Fixes: 2dbb60f789cb ("mm/damon/core: implement PSI metric DAMOS quota goal") Signed-off-by: SJ Park Signed-off-by: Andrew Morton Reviewed-by: Lian Wang Tested-by: Lian Wang Reviewed-by: Kunwu Chan Cc: Brendan Higgins Cc: David Gow Cc: Quanmin Yan Cc: # 6.9.x Signed-off-by: Sasha Levin --- mm/damon/core.c | 13 +++++++++++-- mm/damon/tests/core-kunit.h | 9 +++------ 2 files changed, 14 insertions(+), 8 deletions(-) diff --git a/mm/damon/core.c b/mm/damon/core.c index acbf32232c3f3..0463e7ec0e14b 100644 --- a/mm/damon/core.c +++ b/mm/damon/core.c @@ -635,6 +635,8 @@ struct damos_quota_goal *damos_new_quota_goal( return NULL; goal->metric = metric; goal->target_value = target_value; + if (metric == DAMOS_QUOTA_SOME_MEM_PSI_US) + goal->last_psi_total = U64_MAX; INIT_LIST_HEAD(&goal->list); return goal; } @@ -1122,6 +1124,9 @@ static void damos_commit_quota_goal_union( struct damos_quota_goal *dst, struct damos_quota_goal *src) { switch (dst->metric) { + case DAMOS_QUOTA_SOME_MEM_PSI_US: + dst->last_psi_total = U64_MAX; + break; case DAMOS_QUOTA_NODE_MEM_USED_BP: case DAMOS_QUOTA_NODE_MEM_FREE_BP: dst->nid = src->nid; @@ -1145,7 +1150,6 @@ static int damos_commit_quota_goal( dst->target_value = src->target_value; if (dst->metric == DAMOS_QUOTA_USER_INPUT) dst->current_value = src->current_value; - /* keep last_psi_total as is, since it will be updated in next cycle */ damos_commit_quota_goal_union(dst, src); return 0; } @@ -3045,7 +3049,12 @@ static void damos_set_quota_goal_current_value(struct damon_ctx *c, break; case DAMOS_QUOTA_SOME_MEM_PSI_US: now_psi_total = damos_get_some_mem_psi_total(); - goal->current_value = now_psi_total - goal->last_psi_total; + /* uninitialized last_psi_total; make no effect this round */ + if (goal->last_psi_total == U64_MAX) + goal->current_value = goal->target_value; + else + goal->current_value = now_psi_total - + goal->last_psi_total; goal->last_psi_total = now_psi_total; break; case DAMOS_QUOTA_NODE_MEM_USED_BP: diff --git a/mm/damon/tests/core-kunit.h b/mm/damon/tests/core-kunit.h index b643f9a83f14a..65443aba03300 100644 --- a/mm/damon/tests/core-kunit.h +++ b/mm/damon/tests/core-kunit.h @@ -751,19 +751,16 @@ static void damos_test_commit_quota_goal_for(struct kunit *test, struct damos_quota_goal *dst, struct damos_quota_goal *src) { - u64 dst_last_psi_total = 0; - - if (dst->metric == DAMOS_QUOTA_SOME_MEM_PSI_US) - dst_last_psi_total = dst->last_psi_total; damos_commit_quota_goal(dst, src); KUNIT_EXPECT_EQ(test, dst->metric, src->metric); KUNIT_EXPECT_EQ(test, dst->target_value, src->target_value); if (src->metric == DAMOS_QUOTA_USER_INPUT) KUNIT_EXPECT_EQ(test, dst->current_value, src->current_value); - if (dst_last_psi_total && src->metric == DAMOS_QUOTA_SOME_MEM_PSI_US) - KUNIT_EXPECT_EQ(test, dst->last_psi_total, dst_last_psi_total); switch (dst->metric) { + case DAMOS_QUOTA_SOME_MEM_PSI_US: + KUNIT_EXPECT_EQ(test, dst->last_psi_total, U64_MAX); + break; case DAMOS_QUOTA_NODE_MEM_USED_BP: case DAMOS_QUOTA_NODE_MEM_FREE_BP: KUNIT_EXPECT_EQ(test, dst->nid, src->nid); -- 2.53.0