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Message-ID: <x2675vjrcxax375coeazrvfegtxasr74saf44mrb4npf5cgdr2@cg7gajuen7ni>
Date: Tue, 16 Dec 2025 14:30:20 +0800
From: Vernon Yang <vernon2gm@...il.com>
To: kernel test robot <lkp@...el.com>
Cc: akpm@...ux-foundation.org, david@...nel.org,
lorenzo.stoakes@...cle.com, llvm@...ts.linux.dev, oe-kbuild-all@...ts.linux.dev,
ziy@...dia.com, baohua@...nel.org, lance.yang@...ux.dev, linux-mm@...ck.org,
linux-kernel@...r.kernel.org, Vernon Yang <yanglincheng@...inos.cn>
Subject: Re: [PATCH 2/4] mm: khugepaged: remove mm when all memory has been
collapsed
On Tue, Dec 16, 2025 at 05:45:31AM +0800, kernel test robot wrote:
> Hi Vernon,
>
> kernel test robot noticed the following build errors:
>
> [auto build test ERROR on akpm-mm/mm-everything]
> [also build test ERROR on linus/master v6.19-rc1 next-20251215]
> [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/Vernon-Yang/mm-khugepaged-add-trace_mm_khugepaged_scan-event/20251215-171046
> base: https://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm.git mm-everything
> patch link: https://lore.kernel.org/r/20251215090419.174418-3-yanglincheng%40kylinos.cn
> patch subject: [PATCH 2/4] mm: khugepaged: remove mm when all memory has been collapsed
> config: x86_64-kexec (https://download.01.org/0day-ci/archive/20251216/202512160533.KuHwyJTP-lkp@intel.com/config)
> compiler: clang version 20.1.8 (https://github.com/llvm/llvm-project 87f0227cb60147a26a1eeb4fb06e3b505e9c7261)
> reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20251216/202512160533.KuHwyJTP-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/202512160533.KuHwyJTP-lkp@intel.com/
>
> All errors (new ones prefixed by >>):
>
> >> mm/khugepaged.c:2490:9: error: use of undeclared identifier 'SCAN_PMD_NULL'; did you mean 'SCAN_VMA_NULL'?
> 2490 | case SCAN_PMD_NULL:
> | ^~~~~~~~~~~~~
> | SCAN_VMA_NULL
> mm/khugepaged.c:50:2: note: 'SCAN_VMA_NULL' declared here
> 50 | SCAN_VMA_NULL,
> | ^
> >> mm/khugepaged.c:2491:9: error: use of undeclared identifier 'SCAN_PMD_NONE'
> 2491 | case SCAN_PMD_NONE:
> | ^
> 2 errors generated.
This series is based on Linux v6.18, due to the v6.19-rc1 add "mm/khugepaged:
unify SCAN_PMD_NONE and SCAN_PMD_NULL into SCAN_NO_PTE_TABLE"[1], trigger this
build errors. I'll fix it in the next version, Thanks!
[1] https://lkml.kernel.org/r/20251114030028.7035-4-richard.weiyang@gmail.com
>
> vim +2490 mm/khugepaged.c
>
> 2392
> 2393 static unsigned int khugepaged_scan_mm_slot(unsigned int pages, int *result,
> 2394 struct collapse_control *cc)
> 2395 __releases(&khugepaged_mm_lock)
> 2396 __acquires(&khugepaged_mm_lock)
> 2397 {
> 2398 struct vma_iterator vmi;
> 2399 struct mm_slot *slot;
> 2400 struct mm_struct *mm;
> 2401 struct vm_area_struct *vma;
> 2402 int progress = 0;
> 2403
> 2404 VM_BUG_ON(!pages);
> 2405 lockdep_assert_held(&khugepaged_mm_lock);
> 2406 *result = SCAN_FAIL;
> 2407
> 2408 if (khugepaged_scan.mm_slot) {
> 2409 slot = khugepaged_scan.mm_slot;
> 2410 } else {
> 2411 slot = list_first_entry(&khugepaged_scan.mm_head,
> 2412 struct mm_slot, mm_node);
> 2413 khugepaged_scan.address = 0;
> 2414 khugepaged_scan.mm_slot = slot;
> 2415 khugepaged_scan.maybe_collapse = false;
> 2416 }
> 2417 spin_unlock(&khugepaged_mm_lock);
> 2418
> 2419 mm = slot->mm;
> 2420 /*
> 2421 * Don't wait for semaphore (to avoid long wait times). Just move to
> 2422 * the next mm on the list.
> 2423 */
> 2424 vma = NULL;
> 2425 if (unlikely(!mmap_read_trylock(mm)))
> 2426 goto breakouterloop_mmap_lock;
> 2427
> 2428 progress++;
> 2429 if (unlikely(hpage_collapse_test_exit_or_disable(mm)))
> 2430 goto breakouterloop;
> 2431
> 2432 vma_iter_init(&vmi, mm, khugepaged_scan.address);
> 2433 for_each_vma(vmi, vma) {
> 2434 unsigned long hstart, hend;
> 2435
> 2436 cond_resched();
> 2437 if (unlikely(hpage_collapse_test_exit_or_disable(mm))) {
> 2438 progress++;
> 2439 break;
> 2440 }
> 2441 if (!thp_vma_allowable_order(vma, vma->vm_flags, TVA_KHUGEPAGED, PMD_ORDER)) {
> 2442 skip:
> 2443 progress++;
> 2444 continue;
> 2445 }
> 2446 hstart = round_up(vma->vm_start, HPAGE_PMD_SIZE);
> 2447 hend = round_down(vma->vm_end, HPAGE_PMD_SIZE);
> 2448 if (khugepaged_scan.address > hend)
> 2449 goto skip;
> 2450 if (khugepaged_scan.address < hstart)
> 2451 khugepaged_scan.address = hstart;
> 2452 VM_BUG_ON(khugepaged_scan.address & ~HPAGE_PMD_MASK);
> 2453
> 2454 while (khugepaged_scan.address < hend) {
> 2455 bool mmap_locked = true;
> 2456
> 2457 cond_resched();
> 2458 if (unlikely(hpage_collapse_test_exit_or_disable(mm)))
> 2459 goto breakouterloop;
> 2460
> 2461 VM_BUG_ON(khugepaged_scan.address < hstart ||
> 2462 khugepaged_scan.address + HPAGE_PMD_SIZE >
> 2463 hend);
> 2464 if (!vma_is_anonymous(vma)) {
> 2465 struct file *file = get_file(vma->vm_file);
> 2466 pgoff_t pgoff = linear_page_index(vma,
> 2467 khugepaged_scan.address);
> 2468
> 2469 mmap_read_unlock(mm);
> 2470 mmap_locked = false;
> 2471 *result = hpage_collapse_scan_file(mm,
> 2472 khugepaged_scan.address, file, pgoff, cc);
> 2473 fput(file);
> 2474 if (*result == SCAN_PTE_MAPPED_HUGEPAGE) {
> 2475 mmap_read_lock(mm);
> 2476 if (hpage_collapse_test_exit_or_disable(mm))
> 2477 goto breakouterloop;
> 2478 *result = collapse_pte_mapped_thp(mm,
> 2479 khugepaged_scan.address, false);
> 2480 if (*result == SCAN_PMD_MAPPED)
> 2481 *result = SCAN_SUCCEED;
> 2482 mmap_read_unlock(mm);
> 2483 }
> 2484 } else {
> 2485 *result = hpage_collapse_scan_pmd(mm, vma,
> 2486 khugepaged_scan.address, &mmap_locked, cc);
> 2487 }
> 2488
> 2489 switch (*result) {
> > 2490 case SCAN_PMD_NULL:
> > 2491 case SCAN_PMD_NONE:
> 2492 case SCAN_PMD_MAPPED:
> 2493 case SCAN_PTE_MAPPED_HUGEPAGE:
> 2494 break;
> 2495 case SCAN_SUCCEED:
> 2496 ++khugepaged_pages_collapsed;
> 2497 fallthrough;
> 2498 default:
> 2499 khugepaged_scan.maybe_collapse = true;
> 2500 }
> 2501
> 2502 /* move to next address */
> 2503 khugepaged_scan.address += HPAGE_PMD_SIZE;
> 2504 progress += HPAGE_PMD_NR;
> 2505 if (!mmap_locked)
> 2506 /*
> 2507 * We released mmap_lock so break loop. Note
> 2508 * that we drop mmap_lock before all hugepage
> 2509 * allocations, so if allocation fails, we are
> 2510 * guaranteed to break here and report the
> 2511 * correct result back to caller.
> 2512 */
> 2513 goto breakouterloop_mmap_lock;
> 2514 if (progress >= pages)
> 2515 goto breakouterloop;
> 2516 }
> 2517 }
> 2518 breakouterloop:
> 2519 mmap_read_unlock(mm); /* exit_mmap will destroy ptes after this */
> 2520 breakouterloop_mmap_lock:
> 2521
> 2522 spin_lock(&khugepaged_mm_lock);
> 2523 VM_BUG_ON(khugepaged_scan.mm_slot != slot);
> 2524 /*
> 2525 * Release the current mm_slot if this mm is about to die, or
> 2526 * if we scanned all vmas of this mm.
> 2527 */
> 2528 if (hpage_collapse_test_exit(mm) || !vma) {
> 2529 bool maybe_collapse = khugepaged_scan.maybe_collapse;
> 2530
> 2531 if (mm_flags_test(MMF_DISABLE_THP_COMPLETELY, mm))
> 2532 maybe_collapse = true;
> 2533
> 2534 /*
> 2535 * Make sure that if mm_users is reaching zero while
> 2536 * khugepaged runs here, khugepaged_exit will find
> 2537 * mm_slot not pointing to the exiting mm.
> 2538 */
> 2539 if (!list_is_last(&slot->mm_node, &khugepaged_scan.mm_head)) {
> 2540 khugepaged_scan.mm_slot = list_next_entry(slot, mm_node);
> 2541 khugepaged_scan.address = 0;
> 2542 khugepaged_scan.maybe_collapse = false;
> 2543 } else {
> 2544 khugepaged_scan.mm_slot = NULL;
> 2545 khugepaged_full_scans++;
> 2546 }
> 2547
> 2548 collect_mm_slot(slot, maybe_collapse);
> 2549 }
> 2550
> 2551 trace_mm_khugepaged_scan(mm, progress, khugepaged_scan.mm_slot == NULL);
> 2552
> 2553 return progress;
> 2554 }
> 2555
>
> --
> 0-DAY CI Kernel Test Service
> https://github.com/intel/lkp-tests/wiki
--
Thanks,
Vernon
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