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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> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: 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