From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-188.mta0.migadu.com (out-188.mta0.migadu.com [91.218.175.188]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id EDE6936F8E9 for ; Tue, 14 Jul 2026 01:51:34 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=91.218.175.188 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1783993896; cv=none; b=pBZwfuAvo059OlavRQRP8XPheSl2rQQQJJItQ3LcNTd1R6W/e42GM9R3EsVTtfnbIRHt7uOmO4P502XBwsHAvffqSnu94EtIT4KuAaw8OCVNWMi2qLvf9k0LZbfwPTmGPvh5lisGDzlnFssptWMZEq9W29TwBwpMzsLWgzLa/HI= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1783993896; c=relaxed/simple; bh=u2WlxDcSxSlWdytS1wl7aN0QbwIZXYpPwlt5AW9arTE=; h=From:To:Cc:Subject:Date:Message-ID:MIME-Version; b=BFVFwBQOec33eh7nxCY66UHtkiortn/EGiLeeNyz4+hJ9tGFbcS99LsqJMvvmK8FoUpJlcY5LDTnuVNk/g5eyGD3OpGNPplMH7dfEDKcO5dhnOS5LSEL+l4AQ+7BUnuEndBn6sEBCWJ09EASZ81aRLzDrx1269/CKii1TmcKejU= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b=kifN5DfT; arc=none smtp.client-ip=91.218.175.188 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b="kifN5DfT" X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1783993893; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding; bh=iaDVF3WuxppNxImS1nHcF1VL6OsrhCsOpkRvEZ8Asik=; b=kifN5DfTV8lnCj/IHHJTFSR5RynbXvrlPDQRBA1r8TOXEBcPS9ssNFn39vguX2dD8h6+3u XMXeymH89qzvBXZHoQ/0TYaRPuqJMZtKsQ2jC39vzmmTR9gMjzgsH0vMsITeV4RHTxC3HC z0kv3zEkEEfGsfKH7rCQnX65rqPUxZg= From: Ye Liu To: Andrew Morton , Zi Yan Cc: Ye Liu , Vlastimil Babka , Suren Baghdasaryan , Michal Hocko , Brendan Jackman , Johannes Weiner , linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: [PATCH v6 0/9] mm/page_owner: misc cleanups Date: Tue, 14 Jul 2026 09:50:59 +0800 Message-ID: <20260714015117.78351-1-ye.liu@linux.dev> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT 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. Ye Liu (9): mm/page_owner: extract skip_buddy_pages() helper to unify buddy page skipping mm/page_owner: add MR_NEVER to enum migrate_reason and use it for last_migrate_reason mm: use enum migrate_reason instead of int for migration reason parameters mm/page_owner: hoist CONFIG_MEMCG to function level for print_page_owner_memcg() mm/page_owner: add missing newline to count_threshold format string mm/page_owner: move free_ts_nsec output to free section in __dump_page_owner() mm/page_owner: drop redundant page_owner prefix from static symbols mm/page_owner: clamp skip_buddy_pages() PFN advance at MAX_ORDER_NR_PAGES boundary mm/page_owner: use memcg_data snapshot to avoid TOCTOU in print_page_owner_memcg() include/linux/hugetlb.h | 9 ++- include/linux/migrate.h | 8 +- include/linux/migrate_mode.h | 1 + include/linux/page_owner.h | 7 +- include/trace/events/migrate.h | 11 +-- mm/hugetlb.c | 3 +- mm/migrate.c | 12 +-- mm/page_owner.c | 135 ++++++++++++++++++-------------- scripts/gdb/linux/page_owner.py | 4 +- 9 files changed, 109 insertions(+), 81 deletions(-) --- v6: - Patch 3: drop unnecessary 'extern' from __folio_set_owner_migrate_reason() declaration in page_owner.h; Adjust the indentation; add Reviewed-by from Lorenzo Stoakes. - Patch 8: clarify commit message wording; add Reviewed-by from Zi Yan and Vlastimil Babka. - Patch 9: rename patch to cover both TOCTOU fixes; also replace page_memcg_check(page) with extracting objcg from the memcg_data snapshot to fix a second TOCTOU issue; add early return for the MEMCG_DATA_OBJEXTS (slab) case. - Link: https://lore.kernel.org/all/20260701061101.344679-1-ye.liu@linux.dev/ v5: - Place the two patches corresponding to the Close connection, patch8 and patch9, together in this part. - Close: https://lore.kernel.org/all/20260625014708.87386-1-ye.liu@linux.dev/ - Link: https://lore.kernel.org/all/20260701012239.315262-1-ye.liu@linux.dev/ v4: - Patch 2: also update scripts/gdb/linux/page_owner.py to use MR_NEVER instead of the hardcoded -1. - https://lore.kernel.org/all/20260630015331.147174-1-ye.liu@linux.dev/ v3: - Patch 2: add MR_NEVER directly to enum migrate_reason instead of using a local MIGRATE_REASON_NONE define (Zi Yan and Vlastimil Babka). - Patch 3 (new): convert all 'int reason' parameters in the migration callchain to 'enum migrate_reason' so the type system reflects the actual semantics. - Patch 7: make threshold_fops a single line. - Link: https://lore.kernel.org/all/20260626020522.28619-1-ye.liu@linux.dev/ v2: - Add cover letter (no code changes). - Link: https://lore.kernel.org/all/20260623065234.31866-2-ye.liu@linux.dev/ -- 2.43.0