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b=jVGSgD5Rp1+S26FlKdh30mQwBmeaUSion/wrJY6TRn2CeLWpMfYSoIijBm3rZOtDn B8NnkxN7gQPYUZSnhffWRW3+IjJgN25XZc0kWkdEt4saUjL70y6fJCeIylbEOlrZY9 Vn64zowOOPPCSxLjw8cVHRskMwr76wGxWYl7Ngcb65fJziF4r6RXv84mJC1eMjatdh GRfsVQ+Tp8dVRCRq2zwU7TWyQMFfqtMVPm+HnrBXiy2n51kutFv6xWmSzmP72dxjPu hXba3PzVdw+dTB3OvyUtkXg126TGuRvrW961FdYoQU4imDSKPhL69VMV5atQqwOKnQ aP0c/0ccLqYBQ== Date: Tue, 20 Jan 2026 15:05:03 +0200 From: Mike Rapoport To: Pratyush Yadav Cc: Andrew Morton , Alexander Graf , Pasha Tatashin , kexec@lists.infradead.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Suren Baghdasaryan Subject: Re: [PATCH v2 2/2] kho: simplify page initialization in kho_restore_page() Message-ID: References: <20260116112217.915803-1-pratyush@kernel.org> <20260116112217.915803-3-pratyush@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260116112217.915803-3-pratyush@kernel.org> X-Rspamd-Server: rspam11 X-Rspamd-Queue-Id: AFAC480012 X-Rspam-User: X-Stat-Signature: 3uut1xuz1ct5amj558zuukmkm4ab7p3a X-HE-Tag: 1768914310-154405 X-HE-Meta: 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 8Y6LiHW/ mOQJmXYSeToCwInPCSP9PZLhQt8rpST6I/FsB9G1sHpOGgL5Qdv67UIza+UAYF6ZbvIwvlO6hCzDvO/0ZVsMdYZhBDsc0CHfg3t582j3M9Sei3wmruSxOkwagym7FUGVJRRl1HToxy27demVDaNi0ApRew659AECPjOq34lIpVYXiAtHP7pWD+br0YdpFieM240a5yUWC966WNjDEPvHHaJlKnddtN2hnKAkK8AYVzJY8xUL0Ogy1J33K0DHZ8fB5piZCA6nUBoys4+LHIdIAwUHTwz+v+Yy0EcVzDVqGg/etAySqUKn6RT2Dp+nPZhuW028n 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, Jan 16, 2026 at 11:22:15AM +0000, Pratyush Yadav wrote: > When restoring a page (from kho_restore_pages()) or folio (from > kho_restore_folio()), KHO must initialize the struct page. The > initialization differs slightly depending on if a folio is requested or > a set of 0-order pages is requested. > > Conceptually, it is quite simple to understand. When restoring 0-order > pages, each page gets a refcount of 1 and that's it. When restoring a > folio, head page gets a refcount of 1 and tail pages get 0. > > kho_restore_page() tries to combine the two separate initialization flow > into one piece of code. While it works fine, it is more complicated to > read than it needs to be. Make the code simpler by splitting the two > initalization paths into two separate functions. This improves > readability by clearly showing how each type must be initialized. > > Signed-off-by: Pratyush Yadav Reviewed-by: Mike Rapoport (Microsoft) > --- > > Changes in v2: > - Use unsigned long for nr_pages. > > kernel/liveupdate/kexec_handover.c | 40 +++++++++++++++++++----------- > 1 file changed, 26 insertions(+), 14 deletions(-) > > diff --git a/kernel/liveupdate/kexec_handover.c b/kernel/liveupdate/kexec_handover.c > index 709484fbf9fd..92da76977684 100644 > --- a/kernel/liveupdate/kexec_handover.c > +++ b/kernel/liveupdate/kexec_handover.c > @@ -219,11 +219,32 @@ static int __kho_preserve_order(struct kho_mem_track *track, unsigned long pfn, > return 0; > } > > +/* For physically contiguous 0-order pages. */ > +static void kho_init_pages(struct page *page, unsigned long nr_pages) > +{ > + for (unsigned long i = 0; i < nr_pages; i++) > + set_page_count(page + i, 1); > +} > + > +static void kho_init_folio(struct page *page, unsigned int order) > +{ > + unsigned long nr_pages = (1 << order); > + > + /* Head page gets refcount of 1. */ > + set_page_count(page, 1); > + > + /* For higher order folios, tail pages get a page count of zero. */ > + for (unsigned long i = 1; i < nr_pages; i++) > + set_page_count(page + i, 0); > + > + if (order > 0) > + prep_compound_page(page, order); > +} > + > static struct page *kho_restore_page(phys_addr_t phys, bool is_folio) > { > struct page *page = pfn_to_online_page(PHYS_PFN(phys)); > unsigned long nr_pages; > - unsigned int ref_cnt; > union kho_page_info info; > > if (!page) > @@ -241,20 +262,11 @@ static struct page *kho_restore_page(phys_addr_t phys, bool is_folio) > > /* Clear private to make sure later restores on this page error out. */ > page->private = 0; > - /* Head page gets refcount of 1. */ > - set_page_count(page, 1); > - > - /* > - * For higher order folios, tail pages get a page count of zero. > - * For physically contiguous order-0 pages every pages gets a page > - * count of 1 > - */ > - ref_cnt = is_folio ? 0 : 1; > - for (unsigned long i = 1; i < nr_pages; i++) > - set_page_count(page + i, ref_cnt); > > - if (is_folio && info.order) > - prep_compound_page(page, info.order); > + if (is_folio) > + kho_init_folio(page, info.order); > + else > + kho_init_pages(page, nr_pages); > > adjust_managed_page_count(page, nr_pages); > return page; > -- > 2.52.0.457.g6b5491de43-goog > -- Sincerely yours, Mike.