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Thu, 06 Aug 2026 10:05:04 -0700 (PDT) Received: from fedora ([2607:fb91:201f:cebc:3a68:390a:144e:1b87]) by smtp.gmail.com with ESMTPSA id a92af1059eb24-13fca50acddsm27805225c88.3.2026.08.06.10.05.02 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 06 Aug 2026 10:05:04 -0700 (PDT) Date: Thu, 6 Aug 2026 12:05:00 -0500 From: Gregory Price To: "Lorenzo Stoakes (ARM)" Cc: linux-mm@kvack.org, damon@lists.linux.dev, linux-kernel@vger.kernel.org, kernel-team@meta.com, sj@kernel.org, akpm@linux-foundation.org, david@kernel.org, ziy@nvidia.com, baolin.wang@linux.alibaba.com, liam@infradead.org, npache@redhat.com, ryan.roberts@arm.com, dev.jain@arm.com, baohua@kernel.org, lance.yang@linux.dev, usama.arif@linux.dev, vbabka@kernel.org, jannh@google.com, matthew.brost@intel.com, joshua.hahnjy@gmail.com, rakie.kim@sk.com, byungchul@sk.com, ying.huang@linux.alibaba.com, apopple@nvidia.com Subject: Re: [PATCH 1/4] mm/damon: defensively skip zone device folios in damon_get_folio() Message-ID: References: <20260728194714.3713735-1-gourry@gourry.net> <20260728194714.3713735-2-gourry@gourry.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: F0FA02000A X-Rspam-User: X-Stat-Signature: nthsmconpg5a7cnizzu95qidr6g6buer X-HE-Tag: 1786035905-188206 X-HE-Meta: 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 vrYyQ4qv 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 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Thu, Aug 06, 2026 at 02:37:59PM +0100, Lorenzo Stoakes (ARM) wrote: > On Tue, Jul 28, 2026 at 03:47:11PM -0400, Gregory Price wrote: > > All DAMON physical- and virtual-address operations obtain their folios > > through damon_get_folio(). That helper already excludes ZONE_DEVICE > > memory implicitly via pfn_to_online_page() and folio_test_lru(), but > > this is inconsistent with other callers in mm/ which test explicitly. > > > > Add an explicit folio_is_zone_device() rejection in damon_get_folio() > > so the guarantee lives in one place and covers every caller uniformly, > > consistent with other mm walkers that reject zone device folios. > > > > Signed-off-by: Gregory Price (Meta) > > Thanks, nice to make it explicit! > > Acked-by: Lorenzo Stoakes (ARM) > SJ Asked me to drop it, so I most likely will, but yeah - this exact patch is a good example of how many footguns zone device gives us. ~Gregory