From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id D83F83074AD; Tue, 24 Jun 2025 16:12:23 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1750781543; cv=none; b=QJFjWrFN7a6a0PszBeP58B10DB0WvhQnWHcnkv+HrIFzjAvLeFDbqFw6UZi8+sDBXHk2yf16SZXAllZudJMCqBeHfrZp3pEc+QFBBeEkQdzmOSKqssNMqmiCvh/fQh+h8YqyoBH7ajgqYItSkExiwrFQ6P5EvevABVZMx+OMWsg= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1750781543; c=relaxed/simple; bh=JOL6WKmjohXqSHITngQz/Wj/wlzmJdN8Xapymilc6Y8=; h=From:To:Cc:Subject:In-Reply-To:References:Date:Message-ID: MIME-Version:Content-Type; b=eJYblAK4vk48EpYTlORXrMhO/pDZp2KcX35doO50ZH5lFV2MYzHMX+2Bs2cxSkmKETsS77wAShSZbpK2smQZ9p802RKDOWSaYE7elgYuvOoGwZI4Rr7Yw8QQ+IHut1hbsaaOK29442/4+1NIpg7pJNwIJGZ3AKWiDmHLghTYxjE= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=tvC6j7Vj; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="tvC6j7Vj" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 8C4F1C4CEF0; Tue, 24 Jun 2025 16:12:15 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1750781543; bh=JOL6WKmjohXqSHITngQz/Wj/wlzmJdN8Xapymilc6Y8=; h=From:To:Cc:Subject:In-Reply-To:References:Date:From; 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) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable 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