From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 8E7EF3191BA; Wed, 2 Sep 2026 02:55:43 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788317745; cv=none; b=W3pmulz27YWmcF5dczKUT+421zU3fDiBHRxxqTIdNc5QJVXLh95SHk98ZQglC13lsiXd6brQOm33U6+oQ7FJcTLOYQQmaDrJL0WTQ8rfpunWqffv+sstkj/HeJl0R9YTuO5sMUsQt3+Ngk/q/ImnvtCxAWypb8kvF00ooxBD4e8= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788317745; c=relaxed/simple; bh=5kYCNGWAl5obE4cEzHTnmImv/2TdZoNDNtYVDFCZLa8=; h=Date:To:From:Subject:Message-Id; b=eosg1Xs6j88/NprIPE3Vt84b9e+Sxj/OBp00c+YSvg5SZIRD4YWvnrhuG+Ah9q8DBxAEtc6FlM6PTfSmi4H++3v4QzAYtd3U81EANGs7stDEpquqmhisuzytalUJN510wMOlFchvlUmlxf+l09aFg6GI00Zllid8I0DlFqHKrk0= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux-foundation.org header.i=@linux-foundation.org header.b=iFe5FmIi; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux-foundation.org header.i=@linux-foundation.org header.b="iFe5FmIi" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 2B5F71F000E9; Wed, 2 Sep 2026 02:55:43 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux-foundation.org; s=korg; t=1788317743; bh=L//7fjCBRNe8MeTLruYiqhCCXaPKhthpEXZqkd081GY=; h=Date:To:From:Subject; b=iFe5FmIi3K4OSpZhv3DOyeAFALhVuey22g7rHzuBXWPvGNav3QqbBzUVqFMi7ybFY 6hI/SlitKyOLLn0I846NY7RpmrJ1AZFItupuG9XhP448Tchpp2Fu2mScBad8XMs0qJ fYDNFBHJS4mm0yqrs7DiMHo6lu8NJnwUiMgi5w90= Date: Tue, 01 Sep 2026 19:55:42 -0700 To: mm-commits@vger.kernel.org,yanquanmin1@huawei.com,stable@vger.kernel.org,davidgow@davidgow.net,brendan.higgins@linux.dev,sj@kernel.org,akpm@linux-foundation.org From: Andrew Morton Subject: + mm-damon-core-handle-uninitialized-damos_quota_goal-last_psi_total.patch added to mm-new branch Message-Id: <20260902025543.2B5F71F000E9@smtp.kernel.org> Precedence: bulk X-Mailing-List: mm-commits@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: The patch titled Subject: mm/damon/core: handle uninitialized damos_quota_goal->last_psi_total has been added to the -mm mm-new branch. Its filename is mm-damon-core-handle-uninitialized-damos_quota_goal-last_psi_total.patch This patch will shortly appear at https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-damon-core-handle-uninitialized-damos_quota_goal-last_psi_total.patch This patch will later appear in the mm-new branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm Note, mm-new is a provisional staging ground for work-in-progress patches, and acceptance into mm-new is a notification for others take notice and to finish up reviews. Please do not hesitate to respond to review feedback and post updated versions to replace or incrementally fixup patches in mm-new. The mm-new branch of mm.git is not included in linux-next If a few days of testing in mm-new is successful, the patch will me moved into mm.git's mm-unstable branch, which is included in linux-next Before you just go and hit "reply", please: a) Consider who else should be cc'ed b) Prefer to cc a suitable mailing list as well c) Ideally: find the original patch on the mailing list and do a reply-to-all to that, adding suitable additional cc's *** Remember to use Documentation/process/submit-checklist.rst when testing your code *** The -mm tree is included into linux-next via various branches at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm and is updated there most days ------------------------------------------------------ From: SJ Park Subject: mm/damon/core: handle uninitialized damos_quota_goal->last_psi_total Date: Tue, 1 Sep 2026 17:27:21 -0700 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 Cc: Brendan Higgins Cc: David Gow Cc: Quanmin Yan Cc: # 6.9.x Signed-off-by: Andrew Morton --- mm/damon/core.c | 13 +++++++++++-- mm/damon/tests/core-kunit.h | 9 +++------ 2 files changed, 14 insertions(+), 8 deletions(-) --- a/mm/damon/core.c~mm-damon-core-handle-uninitialized-damos_quota_goal-last_psi_total +++ a/mm/damon/core.c @@ -697,6 +697,8 @@ struct damos_quota_goal *damos_new_quota 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; } @@ -1190,6 +1192,9 @@ static void damos_commit_quota_goal_unio 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; @@ -1211,7 +1216,6 @@ static void 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); } @@ -3136,7 +3140,12 @@ static void damos_set_quota_goal_current 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: --- a/mm/damon/tests/core-kunit.h~mm-damon-core-handle-uninitialized-damos_quota_goal-last_psi_total +++ a/mm/damon/tests/core-kunit.h @@ -757,19 +757,16 @@ static void damos_test_commit_quota_goal 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); _ Patches currently in -mm which might be from sj@kernel.org are mm-damon-core-skip-applying-scheme-if-region-split-for-quota-fails.patch mm-damon-paddr-respect-folio-end-for-damos_stat.patch mm-damon-paddr-respect-folio-end-for-damos-actions-except-stat.patch mm-damon-vaddr-respect-folio-end-for-damos_stat.patch mm-damon-vaddr-respect-folio-end-for-damos_migrate_hotcold.patch mm-damon-core-handle-extreme-memory-state-in-damon_get_node_mem_bp.patch mm-damon-core-handle-extreme-memory-state-in-get_node_memcg_used_bp.patch mm-damon-core-handle-extreme-memory-state-in-get_in_active_mem_bp.patch mm-damon-core-introduce-damon_filter_type_pgidle_unset.patch mm-damon-paddr-support-pgidle_unset-probe-filter-type.patch mm-damon-sysfs-support-pgidle_unset-probe-filter-type.patch docs-mm-damon-design-document-pgidle_unset-probe-filter-type.patch mm-damon-core-introduce-damon_prep-struct.patch mm-damon-core-commit-preps.patch mm-damon-core-introduce-damon_operations-prep_probes.patch mm-damon-paddr-support-damon_prep.patch mm-damon-sysfs-implement-preps-directory.patch mm-damon-sysfs-implement-preps-nr_preps-file.patch mm-damon-sysfs-create-directories-for-nr_preps-writes.patch mm-damon-sysfs-implement-prep_action-file.patch mm-damon-sysfs-pass-preps-to-damon-core.patch selftests-damon-sysfssh-test-probe-prep-sysfs-files.patch docs-mm-damon-design-document-probe-preps.patch docs-admin-guide-mm-damon-usage-document-probe-preps-sysfs-files.patch docs-abi-damon-document-probe-prep-sysfs-files.patch mm-damon-tests-core-kunit-test-committing-psi-goal-to-psi-goal.patch mm-damon-core-handle-uninitialized-damos_quota_goal-last_psi_total.patch mm-damon-core-copy-nid-for-eligible_mem_bp-damos-quota-goal-commit.patch mm-damon-sysfs-set-next-refresh-jiffies-per-sysfs-context.patch