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=1792947248; b=mTeIvr+0Vg2weBEXH8wHD9k4AAlGTdughXd4VAI6pbZcWYaWtUeeGMNXfCgTwMbN44Pc omWDmDIuDrBImpK2rtPrvl3jg3MSrCdMvnah6h7OmggsEUnb3X96ZWg8JCt1HU6e6JgU/ eSnaqxqhKts6+YZ2T69cM+DS6tbVfTmrg3tamlsoyrGYmxjTijGyD8LwJ7cc14fYZ0CzM jlLh9xr/0Zk4kWvUwJBvbzEoGtk+eEIYdxbOAgfNL0U+khWwnujj0QpF+OxscNu1fMa/k qb4kEw4hxF122kyO30d+w2k0Uf2VE8kaYtrMCHMtGJmmGvfkTdOzuEqcDXogCD624Qg== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1792947248; h=Received:DKIM-Signature:Date:To:From:Subject:Message-Id; bh=7o5Zb9mXHZt3WsgFCTaiwTu3eVbUeCOA9n40KPT6Lwc=; b=y8q8/SnoB795RynGVSl+5DJqBHB7rI15uZDWOhiXXcyare9Wp5g8n2Xd1A+7zW+k1xs5 rRHizDu4VkJTp3mYKMa+voM3t4L6OFclF9KATG5a5wQclDq8M37ABQ8NmbJxxYroA6419 P1w5cMaxF0nA1k2j2piGKMjHpcCzggOcfwO4IOlq9ey9N2hxscky+uV1diEtXidoVAt3m uwBemdiAftwrZlXSBQkwGniZUEq0inhkdjZeJO/GUHNlm5UcF7ZQ1Bo5Ig0UlmN3NPa8X G9ss8SyzfzgpCOskXlnHtMcPs5joafUHgXpSSJisQe4RrjjJVtmgMdjRFrToGUX1+1A== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass header.d=linux-foundation.org header.i=@linux-foundation.org header.a=rsa-sha256 header.s=korg header.b="c/2aiiFE"; 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 3FF8A606A31E; Sun, 25 Oct 2026 16:54:07 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key, unprotected) header.d=linux-foundation.org header.i=@linux-foundation.org header.a=rsa-sha256 header.s=korg header.b=c/2aiiFE Received: by smtp.kernel.org (Postfix) with ESMTPSA id B9AB01F01825; Sun, 25 Oct 2026 16:54:07 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux-foundation.org; s=korg; t=1792947247; bh=7o5Zb9mXHZt3WsgFCTaiwTu3eVbUeCOA9n40KPT6Lwc=; h=Date:To:From:Subject; b=c/2aiiFEDq7C074KU3ZFL02b/XMEQExF/tx28HbgnH1sHYOd3dJcC7BCaLwOaU5HO kEJqncOr65YtFujMsqswSbmM2EVz7KdR9xMPpnMoI+hLatAYiNsae5KGXzCsQpctSO 0LuTZgp34bSm7cKNVJHkiZY4y57icoTOKlFY749c= Date: Sun, 25 Oct 2026 09:54:07 -0700 To: mm-commits@vger.kernel.org,stable@vger.kernel.org,sjpark@amazon.de, sieberf@amazon.com,sj@kernel.org,akpm@linux-foundation.org From: Andrew Morton Subject: + mm-damon-core-move-static-variable-last_nr_regions-to-damon_ctx.patch added to mm-unstable branch Message-Id: <20261025165407.B9AB01F01825@smtp.kernel.org> X-Mailing-List: mm-commits@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list The patch titled Subject: mm/damon/core: move static variable last_nr_regions to damon_ctx has been added to the -mm mm-unstable branch. Its filename is mm-damon-core-move-static-variable-last_nr_regions-to-damon_ctx.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-move-static-variable-last_nr_regions-to-damon_ctx.patch This patch will later appear in the mm-unstable branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm 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: move static variable last_nr_regions to damon_ctx Date: Sun, 25 Oct 2026 09:48:05 -0700 kdamond_split_regions() uses a static variable last_nr_regions, to infer if the region boundaries are too stable. If it looks too stable, it does a more aggressive region split because it might be a fake stability coming from non-aggressive split. Because the variable is static, the inference can be racy and wrong when multiple kdamonds are running in parallel. The user impact is not critical. No crash, no leak. DAMON's best-effort monitoring accuracy can be degraded when multiple kdamonds are used in parallel and the workload has certain access patterns. Still it is a bug that is better to fix. Move the variable into the damon_ctx struct to fix the problem. Link: https://lore.kernel.org/20261025164808.152048-3-sj@kernel.org Fixes: 75c1c2b53c78 ("mm/damon/dbgfs: support multiple contexts") Signed-off-by: SJ Park Signed-off-by: Andrew Morton Closes: https://sashiko.dev/#/bug/linux-eebfcdde-2881-48ef-8df1-e2019d2a47f2 Cc: Fernand Sieber Cc: SeongJae Park Cc: # 5.15.x --- include/linux/damon.h | 5 +++++ mm/damon/core.c | 5 ++--- 2 files changed, 7 insertions(+), 3 deletions(-) --- a/include/linux/damon.h~mm-damon-core-move-static-variable-last_nr_regions-to-damon_ctx +++ a/include/linux/damon.h @@ -958,6 +958,11 @@ struct damon_ctx { /* @rnd_state: Per-ctx PRNG state for damon_rand(). */ struct rnd_state rnd_state; + /* + * number of regions after last merge. Read kdamond_split_regions() + * for more details. + */ + unsigned long last_nr_regions; }; /* Get a random number in [@l, @r) using @ctx's lockless PRNG. */ --- a/mm/damon/core.c~mm-damon-core-move-static-variable-last_nr_regions-to-damon_ctx +++ a/mm/damon/core.c @@ -3795,7 +3795,6 @@ static noinline_for_stack void kdamond_s struct damon_target *t; unsigned long nr_regions = 0; unsigned long max_nr_regions = ctx->attrs.max_nr_regions; - static unsigned long last_nr_regions; int nr_subregions = 2; damon_for_each_target(t, ctx) @@ -3811,7 +3810,7 @@ static noinline_for_stack void kdamond_s } /* Maybe the middle of the region has different access frequency */ - if (last_nr_regions == nr_regions && + if (ctx->last_nr_regions == nr_regions && nr_regions < max_nr_regions / 3) nr_subregions = 3; @@ -3820,7 +3819,7 @@ static noinline_for_stack void kdamond_s ctx->min_region_sz); done: - last_nr_regions = nr_regions; + ctx->last_nr_regions = nr_regions; } /* _ Patches currently in -mm which might be from sj@kernel.org are mm-damon-sysfs-schemes-hold-damon_sysfs_lock-in-target_metric_store.patch mm-damon-core-move-static-variable-last_nr_regions-to-damon_ctx.patch mm-damon-core-move-static-variable-rotation-to-damon_ctx.patch