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Wed, 15 Jan 2025 14:05:42 -0800 (PST) Date: Wed, 15 Jan 2025 14:05:42 -0800 (PST) From: "Christoph Lameter (Ampere)" To: Yang Shi cc: Lorenzo Stoakes , arnd@arndb.de, gregkh@linuxfoundation.org, Liam.Howlett@oracle.com, vbabka@suse.cz, jannh@google.com, willy@infradead.org, liushixin2@huawei.com, akpm@linux-foundation.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] /dev/zero: make private mapping full anonymous mapping In-Reply-To: <0c7fb1b2-4f08-4017-a27c-cc0cb4da4a93@os.amperecomputing.com> Message-ID: References: <20250113223033.4054534-1-yang@os.amperecomputing.com> <2dda50aa-e4a1-4664-b8fa-56ba975db329@lucifer.local> <65691afc-615a-4716-8a2e-1f43bc65111c@os.amperecomputing.com> <3fdcd6a5-27fe-411b-923c-b7410e4cbda9@lucifer.local> <389c72c2-f102-4d32-886b-99d7c212a295@os.amperecomputing.com> <23f50178-59d1-462b-8463-48cc707d6b3f@os.amperecomputing.com> <0c7fb1b2-4f08-4017-a27c-cc0cb4da4a93@os.amperecomputing.com> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: 3A02A10000B X-Stat-Signature: 4cne7mrd8ik385m4xc31bq3o9ocysaqk X-Rspam-User: X-HE-Tag: 1736979324-620761 X-HE-Meta: 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 Fm8CsAUR gz5RTklsGIbiHpi8P46jXz9KqrXokMenibWbVgtIuQJMztn5n8DU2jgTNnx7w8uB5QTqNTieWpFOfGkd0Pfq2PDoBxuKzBzyKHQfo/G671/8v1OpZT3cDFZyi5GgNGFBhXtzFFt2UyWW9PlXasQWX04FBo81i+ZllD//mR7JWAgbwRpsko8+OyBMSyGGLcb4m41pCHaAsTgklxyqAcwobrvCV9ZHZnfu4pf4bOjs1kWQx0l6AlHXTC+lccg== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Wed, 15 Jan 2025, Yang Shi wrote: > > > > I just thought of named anonymous VMA may help. We can give the private > > > /dev/zero mapping a name, for example, just "/dev/zero". However, > > > "[anon:/dev/zero]" will show up in smaps/maps. We can't keep the device > > > numbers and inode number either, but it seems it can tell the user this > > > mapping comes from /dev/zero, and it also explicitly tells us it is > > > specially treated by kernel. Hopefully setting anon_name is permitted. > > But then that'd require CONFIG_ANON_VMA_NAME unfortunately :( > > Yes. Add a counter for NULL pages in smaps? I.e. Null: 4 kB Both anonymous and file mappings could have NULL page references right?