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b=tvC6j7VjREp+BGJeKqV/caHXrqwb4fickgxYpsMh815a0NMBs4DoXS6bY7T759l14 d4pYdByP6Z3FuzrRhGV3WQbAIT/uo5MFTUQCpU0gzaYrM0B1K/DydHhwW/LyybW/Y0 I1fS81yhqfSUTQlvsFShyaqIFi7hr/S6m2KmuK7Cc32Cs0pyXp6Cy/7KmtUsqE++F9 XEcsqlFLfO5CcaHpDNJWJk7dvE/tlgRgZPrmyRP8vFkXZqR8CAMVCZrmmV68TxP8nw VQaNl7gpgX+WCuAGpB1dWUrF5D400I99Xx5EdS6b5vtqShAl26IVInzPqE+NEWPm2w pUXslySxKqqVQ== From: Pratyush Yadav To: Pasha Tatashin Cc: Pratyush Yadav , 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 Subject: Re: [RFC v2 05/16] luo: luo_core: integrate with KHO In-Reply-To: References: <20250617152357.GB1376515@ziepe.ca> Date: Tue, 24 Jun 2025 18:12:14 +0200 Message-ID: User-Agent: Gnus/5.13 (Gnus v5.13) MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: AB66A40010 X-Stat-Signature: 4s519r8z8kp1x1c8xpbffrobk1phhp1e X-Rspam-User: X-HE-Tag: 1750781544-219154 X-HE-Meta: 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 ARAzwEz6 WRK4mdv1gMKKY3IPpQMzJVgpZxKv3uAf1ns6sUCf6WB1o+sfRLguDSn7AQb+EFLYsOWYgjq2KuqOIDGK4NRX9vJGtWPIAGh3xM8abLmX+olZnykHtbmvYD7uS25PDnYEPipzkJlqA6N7XSs3LwXDnkQyKWqjoBxqjUIwh5z7d/3Tk7d4b6E07XP22HwufNFqSC4FFVbSvgqFcp4cKQ+FQjhXoERwCXPtjuGrPdqzxGDBy2X1MglcLHfpLpAUEVvV8D2bSafQ5ghshAXDl44ahxsxsnohmy3fncbMExiIWSFzovypT2JBWHmBHU72pv8lYTJ6L 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 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 mind: >> 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 are >> looking into using this to reduce downtime. Since it pretty much >> overlaps with the hypervisor work for now, I haven't been talking about >> 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. --=20 Regards, Pratyush Yadav