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Wed, 14 Jan 2026 04:12:09 -0800 (PST) MIME-Version: 1.0 References: <3d8398f1-0130-4d3b-ac54-d23877811747@kernel.org> <20260114113635.97621-1-lizhe.67@bytedance.com> <97413239-2bdc-456f-8511-65fb9f1e301c@kernel.org> In-Reply-To: <97413239-2bdc-456f-8511-65fb9f1e301c@kernel.org> From: Mateusz Guzik Date: Wed, 14 Jan 2026 13:11:57 +0100 X-Gm-Features: AZwV_Qhyda5VT99rWo8U4cVfhODtVTVmRJzF6cL6ZtMnMgSKrpNB8Y3wfLPK_qo Message-ID: Subject: Re: [PATCH v2 0/8] Introduce a huge-page pre-zeroing mechanism To: "David Hildenbrand (Red Hat)" Cc: Li Zhe , akpm@linux-foundation.org, ankur.a.arora@oracle.com, fvdl@google.com, joao.m.martins@oracle.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org, mhocko@suse.com, muchun.song@linux.dev, osalvador@suse.de, raghavendra.kt@amd.com Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspamd-Queue-Id: 3E342120004 X-Stat-Signature: 59hs4m3cwx6inzuzb1rqi3e6p8iytjpx X-Rspam-User: X-Rspamd-Server: rspam10 X-HE-Tag: 1768392731-323814 X-HE-Meta: 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 UF1zq+Un /VcNNrH209MjysEddk2uVkpNuGT5TopuQ0pFIRQZKHMzP6qM0HPEjH1pVvRcDuKEflSrNB9NhJ2DMazeih0LBRDRuhYD64qcZJlh3bP+5WIybV/Z3OQhcJEj5KGfbWz1smjngy8R32BuiRoJAnMIpkE6X6UjVdX9fR/xAYUs2zG8c2h4WvPb/ONrLukov/jUqtkN5loDPTJ+BHQao/BZpuV6H7ziNJ4UIJH6qTV1PrJtsk0VtGFxEDdm9L/VMKK3MmBRIdIujC6qe/1po7YK+tl8ivXf8RAl1mhia7A6NCGcEBQgKSYRkmxZyw1Sj8iINdFaYV7lZHCUC7Nx8rraSYKDYr61xuIhrOP0yghhdbyFkZBrendea9oNnNrV6gVXPDWF+qM+YzbHPXYS0BzwD8sSZksKxUAwUwvYtxKcTWbcHORz2UL2XuCo5pTcX+5+KjDgrkHtPBP7kkm4vfkmAwMz8Kg== 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, Jan 14, 2026 at 12:55=E2=80=AFPM David Hildenbrand (Red Hat) wrote: > You said "I wonder if implementing hugepage pre-zeroing directly within > the kernel would be a simpler and more direct way to accelerate VM > creation". > > And I agree. But to make that fly (no user space polling interface), I > was wondering whether we could do it like "init_on_free" and let whoever > frees a hugetlb folio just reinitialize it with 0. > > No kernel thread, no user space thread involved. > i don't see how this is supposed to address the stated problem of zeroing being incredibly expensive. With machinery to pre-zero and depending on availability of CPU time + pages eligible for allocation but not yet zeroed vs vm startups/teardowns frequency, there is some amount of real time which wont be spent waiting on said zeroing because it was already done. Any approach which keeps the overhead with the program allocating the page can't take advantage of it, even if said overhead is paid at the end of its life.