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 037732741B6; Wed, 9 Sep 2026 05:36:53 +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=1788932215; cv=none; b=Dy85TEU7INZFo9srUHEfUnC5wHsPt0hSWmNsiSMCcDY6EGorKOG7Z42LbbYCNufxQrPryKdHQaKbsU/g9nx8iOBmaJ0l1OlBuflR9KoCglOaWEgjkcr3+EoYqZpq/b5GzI8KEGcFgU61Nw2cOIlc7SYfEs27Hn9/PYaDghJmfDI= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788932215; c=relaxed/simple; bh=meZYhDMHSLUpipB4xXq7Qe/qjIDCkvPfEJqyVUAQLpw=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=cO2zQtyDWlrdgAnh3LCWPW56ocly9TzDjZ2lZhmtGiRL6Ui8qFzepdfnlnqtIqMsD72MVFxmwtFm8RkRmOHZ0ADo5GKvXR1JgCJb2sOq7PDaBcoOtK7HhV0a72RD0ndELIfqmlfH8Kl5gU6xZegOhZKC+dKYzD2wUrbOS0nuHdM= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=AbkJ+Cmc; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="AbkJ+Cmc" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 739FB1F00A3A; Wed, 9 Sep 2026 05:36:53 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1788932213; bh=2AOm50bQMj9mYuDoY76KPZ5AVhLteU2u0QZmZc9Q+6Y=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=AbkJ+Cmc9jpu0kh3LuECJVI1w8ARWl5iEkBdohI9GVrZMnCEjlj/TrXAKqK2lFlJL r3isNHskrazV1hcTIT96XWkVi88c5FnldkccX+F8v/8sqH+AQ+hkOxVyjhTi5OvH8K 4Ejk10bDdGm5IOv/S8vBMvZdWEIkF6175dM+8pLY8eeUrujiDOu8tasMaRvHIIhl4u Ykjk8cE76E3vORYd6EdZFqQssO6IAkRR661NS25OF6Y6sb7C0o5K3tRnPNrTbO+kh6 RLwmaJrRFNsMESOKJbWGXjv6O3OzHHifXPsKoHvRbKI7U+k3Zj0GV33zD7yEdmtb0t A8I1iFeVpqu8A== From: SJ Park To: stable@vger.kernel.org Cc: damon@lists.linux.dev, SJ Park , Andrew Morton Subject: [PATCH 6.12.y] mm/damon/paddr: drop last same folio access check reuse optimization Date: Tue, 8 Sep 2026 22:36:46 -0700 Message-ID: <20260909053646.245843-1-sj@kernel.org> X-Mailer: git-send-email 2.47.3 In-Reply-To: <2026090852-morally-preview-efa5@gregkh> References: <2026090852-morally-preview-efa5@gregkh> Precedence: bulk X-Mailing-List: damon@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit It can race when multiple kdamonds are being used. The problem from the race is doubtful, but the gain from the optimization is also doubtful. Simply drop the optimization in favor of code simplicity. The user impact is doubtfully trivial. After all, this kind of interference can happen only by intentional user setup. Even if it happens, it will be rare, and the consequence is degradation of the best-effort monitoring results. No critical consequences like kernel panic or memory corruption happen. The race was discovered [1] by Sashiko. Link: https://lore.kernel.org/20260715031002.108504-5-sj@kernel.org Link: https://lore.kernel.org/20260621204050.10993-1-sj@kernel.org [1] Fixes: a28397beb55b ("mm/damon: implement primitives for physical address space monitoring") Signed-off-by: SJ Park Cc: # 5.16.x Signed-off-by: Andrew Morton (cherry picked from commit f23f0aa62b2f32c2b12f95959fc4603ef81678b2) Signed-off-by: SJ Park --- mm/damon/paddr.c | 20 ++++---------------- 1 file changed, 4 insertions(+), 16 deletions(-) diff --git a/mm/damon/paddr.c b/mm/damon/paddr.c index d4a4d51750f5f..a6b1de97b1e8a 100644 --- a/mm/damon/paddr.c +++ b/mm/damon/paddr.c @@ -148,7 +148,7 @@ static bool damon_folio_young(struct folio *folio) return accessed; } -static bool damon_pa_young(unsigned long paddr, unsigned long *folio_sz) +static bool damon_pa_young(unsigned long paddr) { struct folio *folio = damon_get_folio(PHYS_PFN(paddr)); bool accessed; @@ -157,7 +157,6 @@ static bool damon_pa_young(unsigned long paddr, unsigned long *folio_sz) return false; accessed = damon_folio_young(folio); - *folio_sz = folio_size(folio); folio_put(folio); return accessed; } @@ -165,21 +164,10 @@ static bool damon_pa_young(unsigned long paddr, unsigned long *folio_sz) static void __damon_pa_check_access(struct damon_region *r, struct damon_attrs *attrs) { - static unsigned long last_addr; - static unsigned long last_folio_sz = PAGE_SIZE; - static bool last_accessed; - - /* If the region is in the last checked page, reuse the result */ - if (ALIGN_DOWN(last_addr, last_folio_sz) == - ALIGN_DOWN(r->sampling_addr, last_folio_sz)) { - damon_update_region_access_rate(r, last_accessed, attrs); - return; - } - - last_accessed = damon_pa_young(r->sampling_addr, &last_folio_sz); - damon_update_region_access_rate(r, last_accessed, attrs); + bool accessed; - last_addr = r->sampling_addr; + accessed = damon_pa_young(r->sampling_addr); + damon_update_region_access_rate(r, accessed, attrs); } static unsigned int damon_pa_check_accesses(struct damon_ctx *ctx) -- 2.47.3