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AJvYcCVS/RLqGR0UWf5hWRP23uJTcgIOeotxkJFUkGR5kmwh6NKHmXyhCCZ9ObyRw4Rj5esag7+rQYNjZg==@kvack.org X-Gm-Message-State: AOJu0YxfWmOq6zJuOz5p6O020E12gB+HvYUP4TKtqra8ejmx93u6yOdw DPZBv65pUY2RH7V1aWZAhT7bEVCWG4VvgXjiqV/OM1/GcmAsWEbVgSqfFTgE9t4xKKVDoJ65YTK ictR7/GywAIlSVGF821h20fvf73zKs3f9YfaFE5X/qQ== X-Gm-Gg: ASbGncvPh9yL4ml1MQh/rZtH49CDrG2PbLn73z2Ba0hFApq37gI+iJTb253JYL371BI 1nw1IJdQRSMRlxYTG7AitWD8Txj8SQ4ng0tE9EQkYo47Zzb25nqDtGd161+Z+6eGJzRwvn6Paep 2JBAAUpe2Y4w0PH4E7FGc/MSGgoN0tIprR/LHYK30w X-Google-Smtp-Source: AGHT+IHmzhS+s5DWVIpBCV+GDgZgEUwIzmCN1Z+49uE3dFHG2eUFqSxiWqwoQKMZLKfKxNV1yxiPBpy1n5RYjTOahB4= X-Received: by 2002:a05:622a:1101:b0:4a1:3b18:598a with SMTP id d75a77b69052e-4a7c05fbd48mr986921cf.5.1750784194975; Tue, 24 Jun 2025 09:56:34 -0700 (PDT) MIME-Version: 1.0 References: <20250617152357.GB1376515@ziepe.ca> In-Reply-To: From: Pasha Tatashin Date: Tue, 24 Jun 2025 12:55:57 -0400 X-Gm-Features: AX0GCFup8zCy53y0VodnZFfK3G9WBH8l9G1BP-xRmeFAKvueDCp8EdT_3Y4SA-k Message-ID: Subject: Re: [RFC v2 05/16] luo: luo_core: integrate with KHO To: Pratyush Yadav Cc: Mike Rapoport , Jason Gunthorpe , jasonmiu@google.com, graf@amazon.com, changyuanl@google.com, dmatlack@google.com, rientjes@google.com, corbet@lwn.net, rdunlap@infradead.org, ilpo.jarvinen@linux.intel.com, kanie@linux.alibaba.com, ojeda@kernel.org, aliceryhl@google.com, masahiroy@kernel.org, akpm@linux-foundation.org, tj@kernel.org, yoann.congal@smile.fr, mmaurer@google.com, roman.gushchin@linux.dev, chenridong@huawei.com, axboe@kernel.dk, mark.rutland@arm.com, jannh@google.com, vincent.guittot@linaro.org, hannes@cmpxchg.org, dan.j.williams@intel.com, david@redhat.com, joel.granados@kernel.org, rostedt@goodmis.org, anna.schumaker@oracle.com, song@kernel.org, zhangguopeng@kylinos.cn, linux@weissschuh.net, linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, linux-mm@kvack.org, gregkh@linuxfoundation.org, tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, dave.hansen@linux.intel.com, x86@kernel.org, hpa@zytor.com, rafael@kernel.org, dakr@kernel.org, bartosz.golaszewski@linaro.org, cw00.choi@samsung.com, myungjoo.ham@samsung.com, yesanishhere@gmail.com, Jonathan.Cameron@huawei.com, quic_zijuhu@quicinc.com, aleksander.lobakin@intel.com, ira.weiny@intel.com, andriy.shevchenko@linux.intel.com, leon@kernel.org, lukas@wunner.de, bhelgaas@google.com, wagi@kernel.org, djeffery@redhat.com, stuart.w.hayes@gmail.com Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspam-User: X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: 1D41C1C000D X-Stat-Signature: eg13kmog43957dwqu8ii3e6manhxyo4y X-HE-Tag: 1750784195-353553 X-HE-Meta: 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 WcZEl07b K9zfcHSsIVa4SD9GQ8NPgtJ3kGRBoYDIgo+4+cf4jECYe4dJEyAu3zQJn0UoIuCTRK9Lm6dRKpVTlDxJ9fr2xE8pb/gIp5BxW++frIX3fBhAzmDdcMQwfM/Rr0kYEFJSz17slqk3hMmhSLkGkkHPEdTOBYlyEhHHEkSO/vlGMeXSUHct1NSdxli11AXo1/Aekt6I16WYsdECN5ufni8cw7J+ejvwnh8+NpcsQSyQ6ciI3HlGWun+XPQ2AzfwzptN4ptn2/Cvv2YLvHa/PzKL6FY6mm2Kh60mzq5MQhBXUHUISzsHe6IaO6SpuVaqa56vClee3lRY8MJvKIznKwdvfSP9HQviPVztFFivf 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 Tue, Jun 24, 2025 at 12:12=E2=80=AFPM Pratyush Yadav wrote: > > On Fri, Jun 20 2025, Pasha Tatashin wrote: > > > On Fri, Jun 20, 2025 at 11:28=E2=80=AFAM Pratyush Yadav wrote: > >> On Thu, Jun 19 2025, Pasha Tatashin wrote: > [...] > >> Outside of hypervisor live update, I have a very clear use case in min= d: > >> userspace memory handover (on guest side). Say a guest running an > >> in-memory cache like memcached with many gigabytes of cache wants to > >> reboot. It can just shove the cache into a memfd, give it to LUO, and > >> restore it after reboot. Some services that suffer from long reboots a= re > >> looking into using this to reduce downtime. Since it pretty much > >> overlaps with the hypervisor work for now, I haven't been talking abou= t > >> it as much. > >> > >> Would you also call this use case "live update"? Does it also fit with > >> your vision of where LUO should go? > > > > Yes, absolutely. The use case you described (preserving a memcached > > instance via memfd) is a perfect fit for LUO's vision. > > > > While the primary use case driving this work is supporting the > > preservation of virtual machines on a hypervisor, the framework itself > > is not restricted to that scenario. We define "live update" as the > > process of updating the kernel from one version to another while > > preserving FD-based resources and keeping selected devices > > operational. The machine itself can be running storage, database, > > networking, containers, or anything else. > > > > A good parallel is Kernel Live Patching: we don't distinguish what > > workload is running on a machine when applying a security patch; we > > simply patch the running kernel. In the same way, Live Update is > > designed to be workload-agnostic. Whether the system is running an > > in-memory database, containers, or VMs, its primary goal is to enable > > a full kernel update while preserving the userspace-requested state. > > Okay, then we are on the same page and I can live with whatever name we > go with :-) > > BTW, I think it would be useful to make this clarification on the LUO > docs as well so the intended use case/audience of the API is clear. > Currently the doc string in luo_core.c only talks about hypervisors and > VMs. Thank you for the feedback, I will expand Documentation. Pasha > > -- > Regards, > Pratyush Yadav