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 539C7482D4; Wed, 9 Sep 2026 05:31:59 +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=1788931920; cv=none; b=ZTfNGPEO0zl6m6ODfIpj7W9R5bYvCgxZJP0tfwjFwK6BaqXezZqWVPuWERzlUdCCIAa/xN62Fv8Ji7P96wRVnva+pzngY7deMQOO/HTry/N7Lwp2QPBZhCze7iFtL3v8e1Rj6yHdieJzd4JG5kSH/tXfoXcuaayniwRU6+psmJQ= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788931920; c=relaxed/simple; bh=cqdjiDTVIsx6IF8bjeZK+OtT1PMRLkdsl+pm2e3hleI=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=Cz2/MEFecRdstNSwd7DW3bsCFLlAm6eyT8W8d0Kpnf4+ixxZfmlyY0P/qVQPImWac57XPClo5bTv/kMYCcJpakOG9dpXblbuJ1XqlXipCUNVr70sjhLA1TKiBCYiYbQzGsZgZPVjr0IkO0AOGUyxzwltEInje3IovtFWhBPF06g= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=a2JtgsPl; 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="a2JtgsPl" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 0A65C1F00A3A; Wed, 9 Sep 2026 05:31:59 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1788931919; bh=QN/fsFMxm8cPo+Tfo2o1aH0Vp6Rc2SCZ8s5U2niKkes=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=a2JtgsPlmHw2EckbC6qdJIaZMsmOdcwlGFDgDJPSfCfMkzfDtI6aTTPK2cBB0KDhy bK4hwYnj5Bc+ChlKLhGPjguWIsJ16MXHvye8tSpHHokSe+ZiTT0twk6k+w4XWfDYEN lYyTFFj3FFOWg0M6wd8JjdfVXkQTA2rc0alwRZlgXsxvec8FecFM7me5m1pFSs5oOr wT+NOd7VapDB9/PQ/Gzb9B79L1djLaa8CDSet9mXvz74rZgYn94zA8b1uY0yI0Q9Ks E9/ICkHJty5zLokeF0zdsdPjWBDz1EajYHPKdFZccS68yKeujBQ1rnTWCSUxyZjmFo dbc/SRUwZ+UxQ== From: SJ Park To: stable@vger.kernel.org Cc: damon@lists.linux.dev, SJ Park , Andrew Morton Subject: [PATCH 7.2.y] mm/damon/paddr: drop last same folio access check reuse optimization Date: Tue, 8 Sep 2026 22:31:51 -0700 Message-ID: <20260909053151.242944-1-sj@kernel.org> X-Mailer: git-send-email 2.47.3 In-Reply-To: <2026090851-hulk-tutor-8154@gregkh> References: <2026090851-hulk-tutor-8154@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 f7613ce279a24..b3507b1f62499 100644 --- a/mm/damon/paddr.c +++ b/mm/damon/paddr.c @@ -65,7 +65,7 @@ static void damon_pa_prepare_access_checks(struct damon_ctx *ctx) } } -static bool damon_pa_young(phys_addr_t paddr, unsigned long *folio_sz) +static bool damon_pa_young(phys_addr_t paddr) { struct folio *folio = damon_get_folio(PHYS_PFN(paddr)); bool accessed; @@ -74,7 +74,6 @@ static bool damon_pa_young(phys_addr_t paddr, unsigned long *folio_sz) return false; accessed = damon_folio_young(folio); - *folio_sz = folio_size(folio); folio_put(folio); return accessed; } @@ -82,23 +81,12 @@ static bool damon_pa_young(phys_addr_t paddr, unsigned long *folio_sz) static void __damon_pa_check_access(struct damon_region *r, struct damon_attrs *attrs, unsigned long addr_unit) { - static phys_addr_t last_addr; - static unsigned long last_folio_sz = PAGE_SIZE; - static bool last_accessed; + bool accessed; phys_addr_t sampling_addr = damon_pa_phys_addr( r->sampling_addr, addr_unit); - /* If the region is in the last checked page, reuse the result */ - if (ALIGN_DOWN(last_addr, last_folio_sz) == - ALIGN_DOWN(sampling_addr, last_folio_sz)) { - damon_update_region_access_rate(r, last_accessed, attrs); - return; - } - - last_accessed = damon_pa_young(sampling_addr, &last_folio_sz); - damon_update_region_access_rate(r, last_accessed, attrs); - - last_addr = sampling_addr; + accessed = damon_pa_young(sampling_addr); + damon_update_region_access_rate(r, accessed, attrs); } static unsigned int damon_pa_check_accesses(struct damon_ctx *ctx) -- 2.47.3