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b=Q8LHkD8/pkeUy7tSQ8FtNurSnSf31sqSIMXPeJCQROif9hrZjWnTCPCvP19kd7R0a kaYDzAXMkbnVULpmubYOny7/R5eD6lnEf1pRHFrrjAdW7k88mMlhnzh7QEsi6G2ZNS cGavenQ5cbd1xh8eT2YTxPg33A/LDRJN49JOzoCNwrtSIEkqzOL5UXv8vwQ2jJ3r6e FVjWzeHV59KthJnX0PS+16YZdYSLvT0z2ZH129TE6rnGdFTVk1UBrB2kSfyO0WG6b8 w7W2t2uHIqfC2gh6HOUrnnOf98LUhpdkdyTcv6xrYOf81tzoIyeXti4QdopEWyasD3 Q2lKJrtZpDRJA== Message-ID: <1edfe356-8334-42d2-9d68-7c5bf21a01db@kernel.org> Date: Wed, 14 Jan 2026 13:41:40 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 0/8] Introduce a huge-page pre-zeroing mechanism From: "David Hildenbrand (Red Hat)" To: Mateusz Guzik 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 References: <3d8398f1-0130-4d3b-ac54-d23877811747@kernel.org> <20260114113635.97621-1-lizhe.67@bytedance.com> <97413239-2bdc-456f-8511-65fb9f1e301c@kernel.org> Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Rspam-User: X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: 33CB0140008 X-Stat-Signature: ibamim4z54cspad9juot5568ihhu9aoh X-HE-Tag: 1768394506-720821 X-HE-Meta: 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 o0G6ZHni locV7NXWzEYM+IQKk8Y/EqoXKL1zAshJ1GQaeuTP5egaRRUIM8kqctOhHdu8Oo+heaVDtMoTclaYPBIVoR4r93VLCxWJHXSm8++L5+32AzOYBFfrLFE5Hde3nbhsAdwtHT6SNO+Sm/ut4sfT3j7oTYWld+4KuhnhwaTuTBxqPuGgtl/0AML5G+h7tyBAOrJHavfiA/7Zc6aZcCB+LEzoy5fN8WDVWAH16gUZUxFNC2yT9D2PtdfHmvDJQ7B0T6ipPqNzBALNaNlTCaUlEwAKTzYh+DphGCQ/C25HuWRkDqdI7/fzyjgiUqiNYBQ== 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 1/14/26 13:33, David Hildenbrand (Red Hat) wrote: > On 1/14/26 13:11, Mateusz Guzik wrote: >> On Wed, Jan 14, 2026 at 12:55 PM 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. > > The price of zeroing has to be paid somewhere. > > Currently it's done at allocation time, we could move it to freeing time. > > That would make application startup faster and application shutdown slower. > > And we're aware that application shutdown can be expensive, which is why > e.g., QEMU implements an async shutdown operation, where the MM gets > torn down from another process. Also, just to mention it, assuming a VM is backed by a hugetlb file, the user space thread destroying that file (or parts of it by punshing holes and freeing hugetlb folios) would be paying that price. That could be done whenever there is a CPU to spare to perform some freeing. But again, I think the main motivation here is "increase application startup", not optimize that the zeroing happens at specific points in time during system operation (e.g., when idle etc). -- Cheers David