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Mon, 16 Feb 2026 08:00:01 -0800 (PST) MIME-Version: 1.0 References: <20260214084514.2842745-1-haowenchao22@gmail.com> In-Reply-To: From: Wenchao Hao Date: Mon, 16 Feb 2026 23:59:50 +0800 X-Gm-Features: AaiRm52fIgXASX0clklIgIwAP4FMcTQwHDv3f4RKVwgOcf3J2gFBYLnGQkTPJyY Message-ID: Subject: Re: [PATCH] mm: Add AnonZero accounting for zero-filled anonymous pages To: Kiryl Shutsemau Cc: "David Hildenbrand (Arm)" , Andrew Morton , Lorenzo Stoakes , "Liam R . Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , linux-mm@kvack.org, linux-kernel@vger.kernel.org Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Stat-Signature: 88cgt9ifuhegd4ypqzxbuu8bkfpmjgu7 X-Rspamd-Queue-Id: B18762000D X-Rspam-User: X-Rspamd-Server: rspam04 X-HE-Tag: 1771257602-500187 X-HE-Meta: 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 N18RypBx SPdGsI5zmoFXs3rs4VyNvc3aGqQBOlbYrGljzrSBUg+gC9CTi7lX1VaHA6VbsjST+7UCPdCyO6rJR67SyLOsaKrGjHnTNpRnT0ewx2DbofBgnXawGJHy/iUiB8vAHpEG78YSkMe1t14nAaf4tmW3RQIp1DkyytsiuXOlZuGiGgF/YfTMbp9z1FrEBE4yuTpv6GNlyP171hNz6PdGCpCDIBCiqKWHSdfO4krIzwegnlNwjE+Yj1X08S2ddaM0b19Vb74sBizWijmimpImhpPzsq7ronxE+hIJ71snPtdNYyf3kYMd7LsbAyiUh2vf+vrzAVqzguND1HqvKat+HYNrGmzkr2eJMPHKEXpGq7t7vyuiiUrdLnSG5VkNo5FbY/FYulio0Guyy66k6rJ9BxB77bYoCOA== 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 Mon, Feb 16, 2026 at 7:58=E2=80=AFPM Kiryl Shutsemau wrote: > > On Mon, Feb 16, 2026 at 12:45:13PM +0100, David Hildenbrand (Arm) wrote: > > On 2/16/26 12:34, Kiryl Shutsemau wrote: > > > On Sat, Feb 14, 2026 at 04:45:14PM +0800, Wenchao Hao wrote: > > > > Add kernel command line option "count_zero_page" to track anonymous= pages > > > > have been allocated and mapped to userspace but zero-filled. > > > > > > > > This feature is mainly used to debug large folio mechanism, which > > > > pre-allocates and map more pages than actually needed, leading to m= emory > > > > waste from unaccessed pages. > > > > > > > > Export the result in /proc/pid/smaps as "AnonZero" field. > > > > > > I expect it to slowdown /proc/pid/smaps read substantially. I don't > > > think this line in smaps worth it. > > > > > > > That's why it's enabled through a command line parameter. > > One users want the stat and all users on the machine pay the price? > That's a poor trade off. > > In general, smaps scales poorly. It collects a lot of stats and most of > them are ignored by user. We need something like statx(2) where user can > declare what he is interested in, so kernel won't waste cycles. > I initially considered two approaches: First, exposing the needed information via smaps. This does incur some performance cost but is the simplest to implement. The new feature can be dynamically toggled via a command-line parameter. When disabled, the overhead is negligible=E2=80=94only a minor if check, which is insignifican= t compared to the full smaps cost. Second, adding a new system call or extending madvise with a new command like MADV_GET_ZEROANON. Userspace tools can then use it to measure memory waste from zero-filled anonymous huge pages. This is slightly more complex but minimizes system impact: environments tha= t don=E2=80=99t care about zero-filled anonymous pages pay zero overhead when= the command is not used. The exact implementation approach can be discussed after we confirm whether the upstream kernel needs this debugging feature. Thanks. > Kernel cmdline parameter is the wrong place to declare what stats you > want to see. > > -- > Kiryl Shutsemau / Kirill A. Shutemov