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 4733730648C; Wed, 9 Sep 2026 05:43:02 +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=1788932584; cv=none; b=TgEYOlwk5jH4ldE8xe6o0I/NeTHLpJqSKxK9+xZYb1CXwqpDMUfL5K0BLGacJQ/RTGoV9wnWdZUkVk9MvgbpmrooKYMJT2TxImcgXTPTQWywk9nsSykk+/21Ayh9u8wt8pit0aJ9LKFafWgj4a1oSeFNU9UuUMRis7QfSZiyzao= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788932584; c=relaxed/simple; bh=rr3hEOzS6wNnpn7JbL58jpSP0MguAL6pqxYWDazAArU=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=eukbSKdykPWDjYAPNgo4magJyySavRycQ4NYJar/xqtpmS4yNW2NnFzFHdPoptXLNBeBMTF/fIrVvREKFbSaLswJBSWYkGQjwXIEwbBKwBe9XTgQpk3aMgcUpNv/ue2meqbGMz52PWD4GiWlbdxRF2HBgY/z6Ld82i9+2lRRv5E= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=ZGuqOTOk; 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="ZGuqOTOk" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 70F831F00A3E; Wed, 9 Sep 2026 05:43:02 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1788932582; bh=zf7x3TbXalEJF2sMMhkyWdw4YMTc1v08MJk4nc1HYGk=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=ZGuqOTOkY5Ye+gQ2NavGARPwZJ4AviIjC/FUBAtdyx8hiD0jg6U4jIL2RQLlRmRFg q/KOQgrFtvPOAA4KUc3JsWjwbQFwomgGq2FbM0DdkUbrUQNtmjOsrKxo/4KmpRiOi7 fHV/W2yB2gpxXH6wnPfksr+AhGx9GxD1Z+rgdT53uB6FxTa1nltLq9pY0aEOOu7uMH DB8TqOzDXvjBrToV+XztpWPy4iXIThX5OlWgriTH2N/0qFT3wiDsb4RRyZRMj2sQs/ Sx9xtn+/zYEzfvEfRJMSCXAiDJfAGCub2nR+m+q93FpZXsxNfRBSmFbCNRIfwuQVye mHjTKZ6kjKX+A== From: SJ Park To: stable@vger.kernel.org Cc: damon@lists.linux.dev, SJ Park , Andrew Morton Subject: [PATCH 6.1.y] mm/damon/paddr: drop last same folio access check reuse optimization Date: Tue, 8 Sep 2026 22:42:54 -0700 Message-ID: <20260909054255.253652-1-sj@kernel.org> X-Mailer: git-send-email 2.47.3 In-Reply-To: <2026090853-handoff-bootlace-9e07@gregkh> References: <2026090853-handoff-bootlace-9e07@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 | 21 ++++----------------- 1 file changed, 4 insertions(+), 17 deletions(-) diff --git a/mm/damon/paddr.c b/mm/damon/paddr.c index 7bc8d79c7fa07..d1d047f494aed 100644 --- a/mm/damon/paddr.c +++ b/mm/damon/paddr.c @@ -120,7 +120,7 @@ static bool __damon_pa_young(struct folio *folio, struct vm_area_struct *vma, return !result->accessed; } -static bool damon_pa_young(unsigned long paddr, unsigned long *page_sz) +static bool damon_pa_young(unsigned long paddr) { struct folio *folio; struct page *page = damon_get_page(PHYS_PFN(paddr)); @@ -161,29 +161,16 @@ static bool damon_pa_young(unsigned long paddr, unsigned long *page_sz) folio_put(folio); out: - *page_sz = result.page_sz; return result.accessed; } static void __damon_pa_check_access(struct damon_region *r) { - static unsigned long last_addr; - static unsigned long last_page_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_page_sz) == - ALIGN_DOWN(r->sampling_addr, last_page_sz)) { - if (last_accessed) - r->nr_accesses++; - return; - } + bool accessed; - last_accessed = damon_pa_young(r->sampling_addr, &last_page_sz); - if (last_accessed) + accessed = damon_pa_young(r->sampling_addr); + if (accessed) r->nr_accesses++; - - last_addr = r->sampling_addr; } static unsigned int damon_pa_check_accesses(struct damon_ctx *ctx) -- 2.47.3