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Message-ID: <202510151358.YFw4KsDG-lkp@intel.com>
Date: Wed, 15 Oct 2025 13:46:26 +0800
From: kernel test robot <lkp@...el.com>
To: Pedro Demarchi Gomes <pedrodemargomes@...il.com>,
Andrew Morton <akpm@...ux-foundation.org>,
David Hildenbrand <david@...hat.com>
Cc: llvm@...ts.linux.dev, oe-kbuild-all@...ts.linux.dev,
Linux Memory Management List <linux-mm@...ck.org>,
Xu Xin <xu.xin16@....com.cn>,
Chengming Zhou <chengming.zhou@...ux.dev>,
linux-kernel@...r.kernel.org,
Pedro Demarchi Gomes <pedrodemargomes@...il.com>
Subject: Re: [PATCH v2] ksm: use range-walk function to jump over holes in
scan_get_next_rmap_item
Hi Pedro,
kernel test robot noticed the following build warnings:
[auto build test WARNING on akpm-mm/mm-everything]
[also build test WARNING on linus/master v6.18-rc1 next-20251014]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch#_base_tree_information]
url: https://github.com/intel-lab-lkp/linux/commits/Pedro-Demarchi-Gomes/ksm-use-range-walk-function-to-jump-over-holes-in-scan_get_next_rmap_item/20251014-231721
base: https://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm.git mm-everything
patch link: https://lore.kernel.org/r/20251014151126.87589-1-pedrodemargomes%40gmail.com
patch subject: [PATCH v2] ksm: use range-walk function to jump over holes in scan_get_next_rmap_item
config: riscv-randconfig-002-20251015 (https://download.01.org/0day-ci/archive/20251015/202510151358.YFw4KsDG-lkp@intel.com/config)
compiler: clang version 22.0.0git (https://github.com/llvm/llvm-project 39f292ffa13d7ca0d1edff27ac8fd55024bb4d19)
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20251015/202510151358.YFw4KsDG-lkp@intel.com/reproduce)
If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@...el.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202510151358.YFw4KsDG-lkp@intel.com/
All warnings (new ones prefixed by >>):
>> mm/ksm.c:2604:2: warning: label followed by a declaration is a C23 extension [-Wc23-extensions]
2604 | struct ksm_walk_private walk_private = {
| ^
1 warning generated.
Kconfig warnings: (for reference only)
WARNING: unmet direct dependencies detected for ARCH_HAS_ELF_CORE_EFLAGS
Depends on [n]: BINFMT_ELF [=n] && ELF_CORE [=n]
Selected by [y]:
- RISCV [=y]
vim +2604 mm/ksm.c
2527
2528 static struct ksm_rmap_item *scan_get_next_rmap_item(struct page **page)
2529 {
2530 struct mm_struct *mm;
2531 struct ksm_mm_slot *mm_slot;
2532 struct mm_slot *slot;
2533 struct ksm_rmap_item *rmap_item;
2534 int nid;
2535
2536 if (list_empty(&ksm_mm_head.slot.mm_node))
2537 return NULL;
2538
2539 mm_slot = ksm_scan.mm_slot;
2540 if (mm_slot == &ksm_mm_head) {
2541 advisor_start_scan();
2542 trace_ksm_start_scan(ksm_scan.seqnr, ksm_rmap_items);
2543
2544 /*
2545 * A number of pages can hang around indefinitely in per-cpu
2546 * LRU cache, raised page count preventing write_protect_page
2547 * from merging them. Though it doesn't really matter much,
2548 * it is puzzling to see some stuck in pages_volatile until
2549 * other activity jostles them out, and they also prevented
2550 * LTP's KSM test from succeeding deterministically; so drain
2551 * them here (here rather than on entry to ksm_do_scan(),
2552 * so we don't IPI too often when pages_to_scan is set low).
2553 */
2554 lru_add_drain_all();
2555
2556 /*
2557 * Whereas stale stable_nodes on the stable_tree itself
2558 * get pruned in the regular course of stable_tree_search(),
2559 * those moved out to the migrate_nodes list can accumulate:
2560 * so prune them once before each full scan.
2561 */
2562 if (!ksm_merge_across_nodes) {
2563 struct ksm_stable_node *stable_node, *next;
2564 struct folio *folio;
2565
2566 list_for_each_entry_safe(stable_node, next,
2567 &migrate_nodes, list) {
2568 folio = ksm_get_folio(stable_node,
2569 KSM_GET_FOLIO_NOLOCK);
2570 if (folio)
2571 folio_put(folio);
2572 cond_resched();
2573 }
2574 }
2575
2576 for (nid = 0; nid < ksm_nr_node_ids; nid++)
2577 root_unstable_tree[nid] = RB_ROOT;
2578
2579 spin_lock(&ksm_mmlist_lock);
2580 slot = list_entry(mm_slot->slot.mm_node.next,
2581 struct mm_slot, mm_node);
2582 mm_slot = mm_slot_entry(slot, struct ksm_mm_slot, slot);
2583 ksm_scan.mm_slot = mm_slot;
2584 spin_unlock(&ksm_mmlist_lock);
2585 /*
2586 * Although we tested list_empty() above, a racing __ksm_exit
2587 * of the last mm on the list may have removed it since then.
2588 */
2589 if (mm_slot == &ksm_mm_head)
2590 return NULL;
2591 next_mm:
2592 ksm_scan.address = 0;
2593 ksm_scan.rmap_list = &mm_slot->rmap_list;
2594 }
2595
2596 slot = &mm_slot->slot;
2597 mm = slot->mm;
2598
2599 mmap_read_lock(mm);
2600 if (ksm_test_exit(mm))
2601 goto no_vmas;
2602
2603 get_page:
> 2604 struct ksm_walk_private walk_private = {
2605 .page = NULL,
2606 .folio = NULL,
2607 .vma = NULL
2608 };
2609
2610 walk_page_range(mm, ksm_scan.address, -1, &walk_ops, (void *) &walk_private);
2611 if (walk_private.page) {
2612 flush_anon_page(walk_private.vma, walk_private.page, ksm_scan.address);
2613 flush_dcache_page(walk_private.page);
2614 rmap_item = get_next_rmap_item(mm_slot,
2615 ksm_scan.rmap_list, ksm_scan.address);
2616 if (rmap_item) {
2617 ksm_scan.rmap_list =
2618 &rmap_item->rmap_list;
2619
2620 ksm_scan.address += PAGE_SIZE;
2621 if (should_skip_rmap_item(walk_private.folio, rmap_item)) {
2622 folio_put(walk_private.folio);
2623 goto get_page;
2624 }
2625
2626 *page = walk_private.page;
2627 } else {
2628 folio_put(walk_private.folio);
2629 }
2630 mmap_read_unlock(mm);
2631 return rmap_item;
2632 }
2633
2634 if (ksm_test_exit(mm)) {
2635 no_vmas:
2636 ksm_scan.address = 0;
2637 ksm_scan.rmap_list = &mm_slot->rmap_list;
2638 }
2639 /*
2640 * Nuke all the rmap_items that are above this current rmap:
2641 * because there were no VM_MERGEABLE vmas with such addresses.
2642 */
2643 remove_trailing_rmap_items(ksm_scan.rmap_list);
2644
2645 spin_lock(&ksm_mmlist_lock);
2646 slot = list_entry(mm_slot->slot.mm_node.next,
2647 struct mm_slot, mm_node);
2648 ksm_scan.mm_slot = mm_slot_entry(slot, struct ksm_mm_slot, slot);
2649 if (ksm_scan.address == 0) {
2650 /*
2651 * We've completed a full scan of all vmas, holding mmap_lock
2652 * throughout, and found no VM_MERGEABLE: so do the same as
2653 * __ksm_exit does to remove this mm from all our lists now.
2654 * This applies either when cleaning up after __ksm_exit
2655 * (but beware: we can reach here even before __ksm_exit),
2656 * or when all VM_MERGEABLE areas have been unmapped (and
2657 * mmap_lock then protects against race with MADV_MERGEABLE).
2658 */
2659 hash_del(&mm_slot->slot.hash);
2660 list_del(&mm_slot->slot.mm_node);
2661 spin_unlock(&ksm_mmlist_lock);
2662
2663 mm_slot_free(mm_slot_cache, mm_slot);
2664 /*
2665 * Only clear MMF_VM_MERGEABLE. We must not clear
2666 * MMF_VM_MERGE_ANY, because for those MMF_VM_MERGE_ANY process,
2667 * perhaps their mm_struct has just been added to ksm_mm_slot
2668 * list, and its process has not yet officially started running
2669 * or has not yet performed mmap/brk to allocate anonymous VMAS.
2670 */
2671 mm_flags_clear(MMF_VM_MERGEABLE, mm);
2672 mmap_read_unlock(mm);
2673 mmdrop(mm);
2674 } else {
2675 mmap_read_unlock(mm);
2676 /*
2677 * mmap_read_unlock(mm) first because after
2678 * spin_unlock(&ksm_mmlist_lock) run, the "mm" may
2679 * already have been freed under us by __ksm_exit()
2680 * because the "mm_slot" is still hashed and
2681 * ksm_scan.mm_slot doesn't point to it anymore.
2682 */
2683 spin_unlock(&ksm_mmlist_lock);
2684 }
2685
2686 /* Repeat until we've completed scanning the whole list */
2687 mm_slot = ksm_scan.mm_slot;
2688 if (mm_slot != &ksm_mm_head)
2689 goto next_mm;
2690
2691 advisor_stop_scan();
2692
2693 trace_ksm_stop_scan(ksm_scan.seqnr, ksm_rmap_items);
2694 ksm_scan.seqnr++;
2695 return NULL;
2696 }
2697
--
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