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AJvYcCUBoxUIxwcNBkpaUy7SW3AQZ1O0Me37BB0FpjPTcT+ek8qmNvKky7dT4qTkhi2BRd0Ai5/OWX4wow==@kvack.org X-Gm-Message-State: AOJu0YzO9ARg0W8x9y7K48RrX8tEf3ggzFuWK2XAIbiDvWoZ9k594IU/ Ut5qWf+V8JxYIk9pkY3Wdosz2jCeHBI6OgCdf6JQ8MAwVLfdzUGycBVhbWIFfzZAjozbnPO1ITy vZt9sdcQ4fvgf1bO8zYNkJDKlUa6vugr01RkfSCc6PA== X-Gm-Gg: AY/fxX6QBWxnYmNOt8q1Q0qbPNOEGZiAFEuC1GtoJbnOCWHTNxk798tgiT5iJNYmp1F 07hwrJDbnNlPTax5ddFn+aJiVueDUHbEDJI37nD3g7SOqeqSuePBIghvQxAT9yvJLbGwEQdbGbG SycxydKEWT28rhdNa9CGFCIYOwcGGkYk9B9SFazLv3j6h74tYLrBMdaNczBSBbDHx36mO32r0Us AHB7Shrn0Qwn7I5qVcx8O5cKRSRVf9S1gIfmFRcKSrdfp9EjXQcp43KlVzAi3dU5zPu6kZ8wHT3 4vtlmYU3u3ECz8W96z38eFYLyg== X-Google-Smtp-Source: AGHT+IGaOrb4zzhWvIUS63W6GXcdLWTjekK8oVCYKzqKxlL53BXhoc0Q/MVLf36WUVWDul8F8ozYwETiXuQjQyiwqgY= X-Received: by 2002:a05:6402:278f:b0:64d:3b22:a595 with SMTP id 4fb4d7f45d1cf-65097dea481mr19954950a12.12.1768321024711; Tue, 13 Jan 2026 08:17:04 -0800 (PST) MIME-Version: 1.0 References: <20260109001127.2596222-1-jasonmiu@google.com> <20260109001127.2596222-2-jasonmiu@google.com> <20260112143904.GA812923@nvidia.com> <20260113130526.GE812923@nvidia.com> <20260113145802.GA900112@nvidia.com> In-Reply-To: <20260113145802.GA900112@nvidia.com> From: Pasha Tatashin Date: Tue, 13 Jan 2026 11:16:27 -0500 X-Gm-Features: AZwV_QhiFAqf5sxAvex6xIJLGyJLdLw2dMrpAVVtkd_ClURKVqujFiU__7SUlmA Message-ID: Subject: Re: [PATCH v4 1/2] kho: Adopt radix tree for preserved memory tracking To: Jason Gunthorpe Cc: Mike Rapoport , Jason Miu , Alexander Graf , Andrew Morton , Baoquan He , Changyuan Lyu , David Matlack , David Rientjes , Pratyush Yadav , kexec@lists.infradead.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspamd-Queue-Id: C6F2480004 X-Rspamd-Server: rspam06 X-Stat-Signature: 66uhj1k4e64d8xjw5pzbdgeb5cmksnn4 X-Rspam-User: X-HE-Tag: 1768321026-48924 X-HE-Meta: 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 MIZvDxTP IZzHkKBIr4J/j1y1haizCvtERuQom3PpBYLMJVR14y8s62fYqQIce2aAN+sxsJmZ3bbPxfIO9CV5Nbb2DtcU3JPKHJI9Usjar6/GDhlYMMDnFfJnetttLSmidTdOYaRABxZUlXidP7q3JhH6gGC/kcSsmBo7jBtjUy8KjU40G1LVSSDPhcCCwDbEmtgmfBG4HYomI0E64Rgq01EhuzNTBau7ZJTeqJUwfDQOl7b18Yx8b8o8nQ3FG7HvJA1HdTPMn6YIQvn1FvyzrJJu09p5NgHwocFcCVgchDNFmasUmvlItO6Y= 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, Jan 13, 2026 at 9:58=E2=80=AFAM Jason Gunthorpe wr= ote: > > On Tue, Jan 13, 2026 at 04:46:01PM +0200, Mike Rapoport wrote: > > On Tue, Jan 13, 2026 at 09:05:26AM -0400, Jason Gunthorpe wrote: > > > On Tue, Jan 13, 2026 at 01:34:42PM +0200, Mike Rapoport wrote: > > > > > > > For example mshv intends to use kho_radix_tree to track the hypervi= sor > > > > memory and there unpreserving will be a part of the normal flow. > > > > > > I do not think this is a good idea. > > > > Sorry I wasn't clear, mshv is not going to use KHO memory tracker but > > another instance of kho_radix_tree data structure. > > I don't see a problem with that. > > Oh.. That's.. Interesting but sure if it is made into a library then > it makes some sense that it would need freeing support somehow. > > I'm surprised there isn't a better data structure for what mshv needs > though? It seems both MSHV and kho_radix_tree have an ABI requirement for data to be parsable by the next kernel. Even if other libraries might work better, they likely won't need to meet the stability and versioning requirements for cross-kernel interfaces. > > > > Nothing should be touching KHO until a kexec sequence is started. KHO > > > calls should WARN_ON prior to this point. If a kexec sequence aborts > > > then the entire radix tree should be discarded and it should go back > > > to WARN_ON'ing KHO calls. > > > > The whole point of making KHO stateless was to decouple it from kexec > > sequence and let userspace control when preservation happens and to all= ow > > preserving as much as possible ahead of time to save cycles at > > kexec-reboot. > > Sure, but also the data structures should not have a life of their > own, it needs to start from an empty slate every time luo starts the > sequence. There cannot be cruft left over from previous failed > attempts or something Even if a kexec fails, as long as someone still holds LUO session references, we might successfully kexec the next time. KHO unpreserving will only occur once the LUO session FDs are closed. Pasha