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t=1768247537; bh=fgj6BnpZP0mq/BZzAj9yNQ2clZzsLqxwm5wCzASP7xA=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=h3T7yleDxgR8/TRdeqFNkgakqO+XXW3YOWE+bpGhvbAP3f+JTyn02RlAyO6PPWzWA AG0kZJ1cpe1IafbJTADNLxNR7AvHOP5EDY6dwhygnZ0tLp1Ag/f9wAoP1ozGf3NXi/ XJgJ9qY+rib9SNX8dyBgBCbhVaQTzIGVE4EwueaASyKOEOcTqR3nH77EbwHMqBJ0ND DjHMGC1m4hdGQ8PaoCGctiGJB+vOXTgUPFspycKSp/ax5ux7mjR9HNu55xF/qZJB6y u2qggj5lH3nvrTFl8fsOrCz84UDRzpujzETNJyG5peWBRTYkeZXRg1PvLQeUIGwXgh 2HxfDYjhrugrg== Message-ID: Date: Mon, 12 Jan 2026 20:52:12 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 0/8] Introduce a huge-page pre-zeroing mechanism To: Li Zhe , muchun.song@linux.dev Cc: akpm@linux-foundation.org, fvdl@google.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org, osalvador@suse.de, mjguzik@gmail.com, mhocko@suse.com, joao.m.martins@oracle.com, ankur.a.arora@oracle.com, raghavendra.kt@amd.com References: <1981A332-0585-49AB-9ADE-99FA2FB32DD4@linux.dev> <20260112112728.94590-1-lizhe.67@bytedance.com> From: "David Hildenbrand (Red Hat)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Stat-Signature: o8maiw7ibxpizbz1zgr7b85pncir5869 X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: E7DD640002 X-Rspam-User: X-HE-Tag: 1768247538-688486 X-HE-Meta: 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 rkRhHJFp RUanUX02CyJK48815D34m+ClKspABOHkUEQMC+xUYwtRosokAcABfbfr0Mb+Vi5MZsgw+dC4AHTrQcV1eL0nW1YEavkEm8jRoWSNdIgEHV+qOAPuscuETktfSYxjD31E1GUOybs3f6HtrafHEXxmMHVzccXCZIDNDEJWERPPqw9nwL88k8wz9jWTGlOVjiyuVzjsL1p9ilMu6wYCXhwTQhB3q6Pu1rsw0ZMbLIg2575Puuf4IIpJ1Bj38Ost9AFyqA6k92zz+AL4zif6M+WgxVO2qcV60Yil5O9Pb 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: > As for concern (4), I believe it is orthogonal to this patchset, and > the cover letter already contains a performance comparison that > demonstrates the additional benefit. > >> I did see some comments in [1] about QEMU supporting user-mode >> parallel zero-page operations; I’m just not sure what the current >> state of that support looks like, or what the corresponding benchmark >> numbers are. > > As noted above, QEMU already employs a parallel page-touch mechanism, > yet the elapsed time remains noticeable. I am not deeply familiar with > QEMU; please correct me if I am mistaken. I implemented some part of the parallel preallocation support in QEMU. With QEMU, you can specify the number of threads and even specify the NUMA-placement of these threads. So you can pretty much fine-tune that for an environment. You still pre-zero all hugetlb pages at VM startup time, just in parallel though. So you pay some price at APP startup time. If you know that you will run such a VM (or something else) later, you could pre-zero the memory from user space by using a hugetlb-backed file and supplying that to QEMU as memory backend for the VM. Then, you can start your VM without any pre-zeroing. I guess that approach should work universally. Of course, there are limitations, as you would have to know how much memory an app needs, and have a way to supply that memory in form of a file to that app. -- Cheers David