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b=shaZyKxLgMY8DS0iCKCgkVYFlABwij1skMdGY9k3ZPmigFjci2tnfEFztXKlJA1bS GEPb5CloQZq2aY9yamsUPgO/kHWjiVvE9z3nFAwVchbx+2n5BgQo5ZJRlywt92MiYl GdGUp1wufn4YUtmHNH8uWQpMyN8q1N0eeahFxUDAmeghZMjM6t+e9uQCgE5JIo1P4p /PGIhT7Ez+s7bYKO8e9qFQdWK6uLhsRYAA+vyHAEfJ3fEwOY4x5gCQnC8so/tvlqLr QVqLlNOihd5SMjkGER2LZoiNBUFPP45NoV1QsKqCQPkocjt9Rv4JAbAtC66S5JnHs2 1t9M6BxvlvARQ== Date: Mon, 31 Mar 2025 17:50:28 +0300 From: Mike Rapoport To: David Woodhouse Cc: Andrew Morton , "Sauerwein, David" , Anshuman Khandual , Ard Biesheuvel , Catalin Marinas , David Hildenbrand , Marc Zyngier , Mark Rutland , Mike Rapoport , Will Deacon , kvmarm@lists.cs.columbia.edu, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: Re: [PATCH v4 2/4] memblock: update initialization of reserved pages Message-ID: References: <20210511100550.28178-1-rppt@kernel.org> <20210511100550.28178-3-rppt@kernel.org> <9f33c0b4517eaf5f36c515b92bdcb6170a4a576a.camel@infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <9f33c0b4517eaf5f36c515b92bdcb6170a4a576a.camel@infradead.org> X-Rspam-User: X-Rspamd-Server: rspam09 X-Rspamd-Queue-Id: 2F9D4180005 X-Stat-Signature: s1idxbyznje4rwhr3ymwwmh7xar6of14 X-HE-Tag: 1743432637-89976 X-HE-Meta: U2FsdGVkX1+GMTZXDD9O4VBlfkY1FR1GTJ7rzAydPXmdDgV+x8lKc7K/pQrtKki3aTx+20KcH9CIoHnlrYbJuZIj+XHDinlA/K1KGsIDEB6Upp5ezOLH5cB/ZyMmFGfRiQP03RmQPQUFsjim/gJi7M9VNsZzocITpnjJayEAACFHfdNyaQvWS0ss/SxNvJq6XYGGtlW5ulPUxNSJsDclFxF0Dw51zDVDlVNCoOng3f0dOOZrUBT4ag5CmUBUaZIy4JhBRkuvMnTkXxjiSHXETPOeJU3sTISp8Pv+zyv0H3ce3RLtC//OaUEuR1+F0uZU0WDvahPRtm5jKNvgj40e18e+P5QX87Cjnng5Wm2ypFsxZXQZImueAR1wTQ7drkQFD7n8u0EqpL1XXATjHb0cOtyAqFObvsIwiFhBk1DQfab6mBGy8Xt+U3lNlqn/9R7/5Giw8KuaJd8/Ak/X8DynoeyJRIOywziyf9Ky0y4DB+bsfEqcfNjowQsBPAig3+H16EOz3PCzG3Ehs/HlyZrQyVp9vr6/LHR3EmFsK/PPNj8Z7AEswLD2PE8jCMbuEPsqCPB4VfzpbDZFN890KjufikxRFR17g3HCm0l0gVinhuLPWQWI9UPSPghNulH1omrB2o9DdeymI6DiI9IQjv5/y0HBQqxjm540mv9XdTSvdK+vcJ3xu9EaYouu9oTzWQUIv9MnTbIRCepl15CGEO+Z8Q/FfJy7SooHEQynfHQS0w9Dc0rsFn7xBoC5f2mEbLX91FcozTAeTR1U07IEtVz/+jYKSTSeJhERNn31hsN9jruWWdGlnqsEQhDkMWB6zLcSlaqX5uWkSx+PQZsFK/YKswC0XyCgHsz/wbE71DWU79Is7bs7p9kiFiOqePuCWGhf767ZIZUytvYUejz/CtdVhhPXSIxKk1CAvB6sb+KTq6x1VWStjNgZo0KEYl9HW2/vs1Znif542UZUlouGHoq 9dyEy+wY M88lG+hZ3v7lCLvCiYI1aKjhADPFlXjQXzB3+rf8RGj6BkKmJZH3GtSpyWssQE5NY8bd2IEyyJGjlERbPQX8wUBr1poNMNL1wEV+QAXkB/Phz4aIcTzjiY6U+oigRiXzHZ71vbxyyb5iLwpFJmDqK99cruCkAXaw8Gxxgur6qX6VzCSqSGy+5p/MVYIoWWUFUkF7IRJv+i4CY0LxBJrGk09naRYnTASl118lCMnMglJJC+AtgZSDV1jARFQ8kTDl/p2G5CvoaUqF3N1VawbUdSAdrLg== 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 Mon, Mar 31, 2025 at 01:50:33PM +0100, David Woodhouse wrote: > On Tue, 2021-05-11 at 13:05 +0300, Mike Rapoport wrote: > >   > > +static void __init memmap_init_reserved_pages(void) > > +{ > > + struct memblock_region *region; > > + phys_addr_t start, end; > > + u64 i; > > + > > + /* initialize struct pages for the reserved regions */ > > + for_each_reserved_mem_range(i, &start, &end) > > + reserve_bootmem_region(start, end); > > + > > + /* and also treat struct pages for the NOMAP regions as PageReserved */ > > + for_each_mem_region(region) { > > + if (memblock_is_nomap(region)) { > > + start = region->base; > > + end = start + region->size; > > + reserve_bootmem_region(start, end); > > + } > > + } > > +} > > + > > In some cases, that whole call to reserve_bootmem_region() may be a no- > op because pfn_valid() is not true for *any* address in that range. > > But reserve_bootmem_region() spends a long time iterating of them all, > and eventually doing nothing: > > void __meminit reserve_bootmem_region(phys_addr_t start, > phys_addr_t end, int nid) > { > unsigned long start_pfn = PFN_DOWN(start); > unsigned long end_pfn = PFN_UP(end); > > for (; start_pfn < end_pfn; start_pfn++) { > if (pfn_valid(start_pfn)) { > struct page *page = pfn_to_page(start_pfn); > > init_reserved_page(start_pfn, nid); > > /* > * no need for atomic set_bit because the struct > * page is not visible yet so nobody should > * access it yet. > */ > __SetPageReserved(page); > } > } > } > > On platforms with large NOMAP regions (e.g. which are actually reserved > for guest memory to keep it out of the Linux address map and allow for > kexec-based live update of the hypervisor), this pointless loop ends up > taking a significant amount of time which is visible as guest steal > time during the live update. > > Can reserve_bootmem_region() skip the loop *completely* if no PFN in > the range from start to end is valid? Or tweak the loop itself to have > an 'else' case which skips to the next valid PFN? Something like > > for(...) { > if (pfn_valid(start_pfn)) { > ... > } else { > start_pfn = next_valid_pfn(start_pfn); > } > } My understanding is that you have large reserved NOMAP ranges that don't appear as memory at all, so no memory map for them is created and so pfn_valid() is false for pfns in those ranges. If this is the case one way indeed would be to make reserve_bootmem_region() skip ranges with no valid pfns. Another way could be to memblock_reserved_mark_noinit() such ranges and then reserve_bootmem_region() won't even get called, but that would require firmware to pass that information somehow. -- Sincerely yours, Mike.