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Patch series "mm/page_owner: misc cleanups", v6. This series collects a few cleanups for mm/page_owner.c that have been accumulated while reading through the file. There is no functional change -- the goal is to make the code easier to read and maintain. Patch 1 consolidates three identical PageBuddy skip blocks into a single skip_buddy_pages() helper, eliminating the duplication and keeping the lockless-read comment in one place. Patch 2 replaces the -1 magic number used for "never migrated" with a proper MR_NEVER member in enum migrate_reason, adds the corresponding "never_migrated" string in the MIGRATE_REASON trace macro, and updates the GDB page_owner script to use MR_NEVER so that lx-dump-page-owner correctly detects unmigrated pages. Patch 3 follows up by converting the remaining 'int reason' parameters throughout the migration and hugetlb callchains to 'enum migrate_reason', making the type explicit and gaining compiler checking. The 'short last_migrate_reason' struct field in page_owner is intentionally left as 'short' since it is per-page metadata where size matters. Patch 4 hoists the CONFIG_MEMCG guard out of print_page_owner_memcg()'s body so that the real implementation and the empty stub are two clearly separate definitions, the common kernel idiom. Patch 5 adds a missing \n to the count_threshold debugfs attribute format string so that cat(1) output is properly terminated. Patch 6 moves free_ts_nsec from the allocation summary line to the free section in __dump_page_owner(), grouping it with free_pid and free_tgid where it logically belongs. This also makes the dump output consistent with print_page_owner(). Patch 7 drops the redundant page_owner_ prefix from file-scoped static symbols (stack_fops, threshold_fops, etc.). Since they cannot collide across translation units, the prefix carries no information. Patch 8 clamps the PFN advance in skip_buddy_pages() at the next MAX_ORDER_NR_PAGES boundary. The lockless buddy_order_unsafe() read can return a garbage order value if the page is concurrently allocated between the PageBuddy check and the private read, potentially causing the PFN to advance past the next bounadry whose pfn_valid() check would have caught an offline memory section. In read_page_owner(), which relies solely on boundary-aligned pfn_valid() to guard pfn_to_page(), this could lead to an unmapped mem_section access. Patch 9 avoids two TOCTOU issues in print_page_owner_memcg() by reusing the page->memcg_data snapshot already taken via READ_ONCE at the top of the function throughout, instead of calling page_memcg_check() and PageMemcgKmem() which re-read page->memcg_data locklessly with VM_BUG_ON assertions. If the page is concurrently freed and reallocated as a THP tail or slab page between the initial guards and these later calls, those assertions can fire on CONFIG_DEBUG_VM=y builds. The OBJEXTS (slab) case is also simplified with an early return since objcg != memcg for slabs. This patch (of 6): Three places in page_owner.c duplicate the same pattern: check if a page is PageBuddy, read its order via buddy_order_unsafe(), advance the pfn past the buddy block if the order is valid, and continue. Consolidate them into a single inline helper skip_buddy_pages(). The function returns true (skip) for any buddy page and advances @pfn past the block when the order is valid; returns false if the page is not a buddy page and should be processed normally. The old init_pages_in_zone() variant used "order > 0" as an extra guard before advancing pfn, but the continue was unconditional and (1UL << 0) - 1 == 0, so the behaviour is identical. The comment about zone->lock is preserved in the helper's kernel-doc. No functional change. Link: https://lore.kernel.org/20260714015117.78351-1-ye.liu@linux.dev Link: https://lore.kernel.org/20260714015117.78351-2-ye.liu@linux.dev Signed-off-by: Ye Liu <ye.liu@linux.dev> Reviewed-by: Zi Yan <ziy@nvidia.com> Reviewed-by: Vlastimil Babka (SUSE) <vbabka@kernel.org> Cc: Brendan Jackman <jackmanb@google.com> Cc: Johannes Weiner <hannes@cmpxchg.org> Cc: Michal Hocko <mhocko@suse.com> Cc: Suren Baghdasaryan <surenb@google.com> Cc: Lorenzo Stoakes <ljs@kernel.org> Cc: David Hildenbrand (Arm) <david@kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Linux kernel ============ The Linux kernel is the core of any Linux operating system. It manages hardware, system resources, and provides the fundamental services for all other software. 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