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X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: oWaexPmX9Pv7Oty/dxqq9Z7Ee9uPWYAG2uEXq/KKEM/0zJbyAxzpH3nGpQEPxIerzMbu07cR2MbJdbYhE4iFUDbdPYlXiVswFFYSEIMZt4dxSzznWQYH++GV/IDWp0NbN5UchvxscFok6jcb51SUyVcU43Cr9lKgPjjQV1J3kdTigKFvr1bJQAzwwipAH4qj0nLXAilfmW0D/33owWmLWwE+wiGhzB8m8HbA8i/9dI3xtfH5JHC5tjOmyoO+sa48JpYeUIJ7UCAELWJgUzjazOIULjd45tjgRJbkYE2NSoWrIfpmw0NNUZ1/HozbqQDCoJX9LUWfN80LEeG3unhIwwPSfJBFxovKSydhLboY99WOWHb5Y7mVXzYxZyGiwL1sumFJTAXnh3mBl4I27+KA/LjgCnvF23SUXSk8lJDvRv7Gsdh3VkkQRxUNNgl/6omq X-OriginatorOrg: arm.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 25 Mar 2026 14:12:06.8833 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 21c88052-f90e-4237-6d09-08de8a787f51 X-MS-Exchange-CrossTenant-Id: f34e5979-57d9-4aaa-ad4d-b122a662184d X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=f34e5979-57d9-4aaa-ad4d-b122a662184d;Ip=[4.158.2.129];Helo=[outbound-uk1.az.dlp.m.darktrace.com] X-MS-Exchange-CrossTenant-AuthSource: DB3PEPF0000885B.eurprd02.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: AS8PR08MB6024 On 24/03/2026 8:56 pm, David Hildenbrand (Arm) wrote: > >> +void __free_contig_range(unsigned long pfn, unsigned long nr_pages) >> +{ >> + struct page *page = pfn_to_page(pfn); >> + struct page *start = NULL; >> + unsigned long start_sec; >> + unsigned long i; >> + bool can_free; >> + >> + /* >> + * Chunk the range into contiguous runs of pages for which the refcount >> + * went to zero and for which free_pages_prepare() succeeded. If >> + * free_pages_prepare() fails we consider the page to have been freed; >> + * deliberately leak it. >> + * >> + * Code assumes contiguous PFNs have contiguous struct pages, but not >> + * vice versa. Break batches at section boundaries since pages from >> + * different sections must not be coalesced into a single high-order >> + * block. > > The comment is not completely accurate: section boundary only applies to > some kernel configs. > > Maybe rewrite the whole paragraph into > > "Contiguous PFNs might not have a contiguous "struct pages" in some > kernel config. Therefore, check memdesc_section(), and stop batching > once it changes, see num_pages_contiguous()." Agreed, I'll update. > >> + */ >> + for (i = 0; i < nr_pages; i++, page++) { >> + VM_WARN_ON_ONCE(PageHead(page)); >> + VM_WARN_ON_ONCE(PageTail(page)); >> + >> + can_free = put_page_testzero(page); >> + if (can_free && !free_pages_prepare(page, 0)) >> + can_free = false; >> + >> + if (can_free && start && >> + memdesc_section(page->flags) != start_sec) { >> + free_prepared_contig_range(start, page - start); >> + start = page; >> + start_sec = memdesc_section(page->flags); >> + } else if (!can_free && start) { >> + free_prepared_contig_range(start, page - start); >> + start = NULL; >> + } else if (can_free && !start) { >> + start = page; >> + start_sec = memdesc_section(page->flags); >> + } >> + } > > Simplification a proposed by Zi make sense to me! I've added it. Thanks, Usama