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[2003:cb:c708:9d00:edd9:835b:4bfb:2ce3]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-38a1c89e278sm4706351f8f.75.2024.12.20.10.32.53 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 20 Dec 2024 10:32:54 -0800 (PST) Message-ID: <36334f20-2b9e-4529-89c4-120678bc5985@redhat.com> Date: Fri, 20 Dec 2024 19:32:52 +0100 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v4 19/25] proc/task_mmu: Ignore ZONE_DEVICE pages To: Alistair Popple Cc: akpm@linux-foundation.org, dan.j.williams@intel.com, linux-mm@kvack.org, lina@asahilina.net, zhang.lyra@gmail.com, gerald.schaefer@linux.ibm.com, vishal.l.verma@intel.com, dave.jiang@intel.com, logang@deltatee.com, bhelgaas@google.com, jack@suse.cz, jgg@ziepe.ca, catalin.marinas@arm.com, will@kernel.org, mpe@ellerman.id.au, npiggin@gmail.com, dave.hansen@linux.intel.com, ira.weiny@intel.com, willy@infradead.org, djwong@kernel.org, tytso@mit.edu, linmiaohe@huawei.com, peterx@redhat.com, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linuxppc-dev@lists.ozlabs.org, nvdimm@lists.linux.dev, linux-cxl@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-ext4@vger.kernel.org, linux-xfs@vger.kernel.org, jhubbard@nvidia.com, hch@lst.de, david@fromorbit.com References: <37rxl2bjda3psdknhboexhbg3hahf5ifmublp5fw7ltdoyqllc@udbz76jklmnu> From: David Hildenbrand Content-Language: en-US Autocrypt: addr=david@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 19.12.24 00:11, Alistair Popple wrote: > On Tue, Dec 17, 2024 at 11:31:25PM +0100, David Hildenbrand wrote: >> On 17.12.24 06:13, Alistair Popple wrote: >>> The procfs mmu files such as smaps currently ignore device dax and fs >>> dax pages because these pages are considered special. To maintain >>> existing behaviour once these pages are treated as normal pages and >>> returned from vm_normal_page() add tests to explicitly skip them. >>> >>> Signed-off-by: Alistair Popple >>> --- >>> fs/proc/task_mmu.c | 18 ++++++++++++++---- >>> 1 file changed, 14 insertions(+), 4 deletions(-) >>> >>> diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c >>> index 38a5a3e..c9b227a 100644 >>> --- a/fs/proc/task_mmu.c >>> +++ b/fs/proc/task_mmu.c >>> @@ -801,6 +801,8 @@ static void smaps_pte_entry(pte_t *pte, unsigned long addr, >>> if (pte_present(ptent)) { >>> page = vm_normal_page(vma, addr, ptent); >>> + if (page && (is_device_dax_page(page) || is_fsdax_page(page))) >> >> This "is_device_dax_page(page) || is_fsdax_page(page)" is a common theme >> here, likely we should have a special helper? > > Sounds good, will add is_dax_page() if there are enough callers left after any > review comments. :) > >> But, don't we actually want to include them in the smaps output now? I think >> we want. > > I'm not an expert in what callers of vm_normal_page() think of as a "normal" > page. Yeah, it's tricky. It means "this is abnormal, don't look at the struct page". We're moving away from that, such that these folios/pages will be ... mostly normal :) > So my philosphy here was to ensure anything calling vm_normal_page() > didn't accidentally start seeing DAX pages, either by checking existing filters > (lots of callers already call vma_is_special_huge() or some equivalent) or > explicitly filtering them out in the hope someone smarter than me could tell me > it was unneccssary. > > That stategy seems to have worked, and so I agree we likely do want them in > smaps. I just didn't want to silently do it without this kind of discussion > first. Yes, absolutely. > >> The rmap code will indicate these pages in /proc/meminfo, per-node info, in >> the memcg ... as "Mapped:" etc. >> >> So likely we just want to also indicate them here, or is there any downsides >> we know of? > > I don't know of any, and I think it makes sense to also indicate them so will > drop this check in the respin. It will be easy to hide them later, at least we talked about it. Thanks for doing all this! -- Cheers, David / dhildenb