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[34.124.129.10]) by smtp.gmail.com with ESMTPSA id 5a478bee46e88-3147d47960dsm11985348eec.0.2026.07.22.14.20.01 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 22 Jul 2026 14:20:23 -0700 (PDT) Date: Wed, 22 Jul 2026 21:19:53 +0000 From: Pranjal Shrivastava To: Mike Rapoport Cc: Pasha Tatashin , Pratyush Yadav , Alexander Graf , Samiullah Khawaja , David Matlack , kexec@lists.infradead.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [RFC PATCH v2 2/2] kho: Introduce preserve/restore APIs for unsplit pages Message-ID: References: <20260713204935.3069000-1-praan@google.com> <20260713204935.3069000-3-praan@google.com> <178456663513.143128.14871307686052703561.b4-review@b4> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <178456663513.143128.14871307686052703561.b4-review@b4> X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: BF4A9100005 X-Rspam-User: X-Stat-Signature: sczb8tk5qw5cx6x4xdy9z8neoyw9nwgg X-HE-Tag: 1784755225-972890 X-HE-Meta: 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 xVNfKPlk bsj/x7fHNFf4JUR7LfIdgwbhIkOXRd4zh4Bp5zsbyg10yPfmCteCQrLRInNUnIdl4cD1f1WvXC8RMtW3DjGjYgXJFdn/IHCIJgwnuv9jKJDXlhh9jsOHzghYIOtIPeM7C4rL5p3PSH38fnPkviJE2Gqh/FtDckSbFMuZNdVZrieeYDkc8bIsVaXADZLemjw2BXJW+nAolzOk1FZqE+ImIBHKn2yHZYHAW58+h/YsVSmedUUuJj0AKUCYrRBiUolGpvqay1Isyhu6d15VuPwO7f9n8mTDZ9//6sPOVd0ZmILLHs4VML0dmmHQrubCrqvHnuhKmA0Iy0PwU2w9I/fs9aRvleMTq6NR0hNR5 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Mon, Jul 20, 2026 at 07:57:15PM +0300, Mike Rapoport wrote: > > The current KHO page preservation APIs (e.g. kho_preserve_pages) assume > > that multi-page blocks are split into independent 4KB pages during > > restoration. This is incompatible with high-order non-compound pages, > > such as DMA buffers, which must be restored with tail pages having a > > zero reference count. > > > > Introduce explicit preserve and restore APIs for unsplit pages, > > high-order non-compound ^ > Ack, will update the commit msg. > > which preserve and restore a high-order page block as a single unit, > > applying a refcount of 1 to the head page while leaving tail pages at 0. > > Rename the existing internal helper to __kho_restore_page(). > > > > Signed-off-by: Pranjal Shrivastava > > > > diff --git a/include/linux/kexec_handover.h b/include/linux/kexec_handover.h > > index 8968c56d2d73e..6e2c75b16209c 100644 > > --- a/include/linux/kexec_handover.h > > +++ b/include/linux/kexec_handover.h > > @@ -22,6 +22,8 @@ bool is_kho_boot(void); > > [...] > > +struct page *kho_restore_page(phys_addr_t phys) > > +{ > > + struct page *page = pfn_to_online_page(PHYS_PFN(phys)); > > + unsigned long nr_pages; > > + union kho_page_info info; > > + > > + if (!page) > > + return NULL; > > + > > + info.page_private = page->private; > > + if (WARN_ON_ONCE(info.magic != KHO_PAGE_MAGIC)) > > + return NULL; > > + > > + nr_pages = (1UL << info.order); > > + page->private = 0; > > + > > + kho_init_unsplit_pages(page, info.order); > > + adjust_managed_page_count(page, nr_pages); > > + > > + return page; > > Hmm, it copies a lot from __kho_init_page(). > We should keep the common part of order-0 page/folio/high-order page > initialization in a single place. > Alright, I'll break out a helper. Thanks, Praan