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[34.83.136.168]) by smtp.gmail.com with ESMTPSA id d2e1a72fcca58-847f6dd9237sm6303930b3a.59.2026.07.07.17.23.58 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 07 Jul 2026 17:23:58 -0700 (PDT) Date: Wed, 8 Jul 2026 00:23:55 +0000 From: Samiullah Khawaja To: Mike Rapoport Cc: Pranjal Shrivastava , Pasha Tatashin , Pratyush Yadav , Alexander Graf , David Matlack , kexec@lists.infradead.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [RFC PATCH 4/4] kho: Introduce kho_split_preserved_pages() helper Message-ID: References: <20260703020832.1731864-1-praan@google.com> <20260703020832.1731864-5-praan@google.com> <178341290877.3292146.993563652569119942.b4-review@b4> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii; format=flowed Content-Disposition: inline In-Reply-To: <178341290877.3292146.993563652569119942.b4-review@b4> X-Rspam-User: X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: 14518100006 X-Stat-Signature: 4inr48bqsojru3crromweu1br45upfud X-HE-Tag: 1783470240-114171 X-HE-Meta: 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 mlIoQe5S ZXbtaFcKH3QqJCOp0HsorDn4q/Mxai051B3AuxrmSxPgoa/LuELa+YlbTJu75Li12ziUJ7PmTSadH2a6RU3sH8BOy38fa53EdV+n0dW1wXDFBvjraKtWH7JsXU3yPz6990+wNZZKXFqGKNfbDmjHPpOS6KCT8hgyAweLV/gpoCafECl9hgK3vU8yzmEq6Adah5zykIXM19JgGCC7jRtmwqCaEnX6i5fqXsp1Hz8Dzeeyk0IHPGH041XiQ3yaQcw0MVT0UluNfv0VJRy9F3ZZmMRAPO4XeEKLr4wvUa6yqh8ZSPn+kQK9x+JwiOWHLhp7dyTwd5Plbs8JTp1USD3O6FxX0Qp/I2sTo0YHhFiIWnhsbBCPQRW4sA2lbzHy7JgvAlxD8SdFhl/WMc1kaBsq82icjfA== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Tue, Jul 07, 2026 at 11:28:28AM +0300, Mike Rapoport wrote: >> A driver may need to split a high-order allocation that has already >> been preserved. If the pages are split using split_page() manually, > >Why? >Are there particular examples? > >> the refcounts would change but KHO won't record the change in the >> preserved page-type, resulting in a metadata mismatch during >> restoration in the new kernel. >> >> Introduce kho_split_preserved_pages() to handle splitting of preserved >> pages. The helper follows an unpreserve -> split -> re-preserve sequence, >> while ensuring that the KHO radix tree is updated with the correct >> KHO_PAGE_SPLIT type bits. >> >> The helper returns 0 on success, or a negative error code if the >> re-preservation fails. Callers must ensure the provided order matches >> the original allocation and that the operation is serialized against >> other preservation API calls. > >Let's put this on hold until there are actual users. +1 I think we discussed in this in one of the hypervisor liveudpate meeting sessions and it was concluded that the split of preseved pages is not needed. > >-- >Sincerely yours, >Mike. >