From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (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 CF8B84F392B for ; Mon, 28 Sep 2026 21:51:07 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790632269; cv=none; b=h9mVQrYhNQxLHFF5Ly4CwuKfmEImt+uoDKPQCC+N1TlWu2ekyM7WwWB5Cu84o6lbTKv3AG/p/FyRNwMmB0+dNhlWzArvQmmjcy9r0o9daj6G8qSJVCw8PHKjmmy/hcxu3CXKqKyiTMilAaSegjthhmOiRJYPsO6zeMITWEU4Mk8= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790632269; c=relaxed/simple; bh=4siHfVdeqd6PzA0Tqsm4EVpsuub1ARjjaRpoyocWqgo=; h=Date:To:From:Subject:Message-Id; b=KxpJLYDVJFzTyepyP7oaY1FERH9AHBsbOaJrxY9E/hHjgcqFKw5fetlROnbgT8oJeTK602kwjFT/CQDMSn8Wami23eDaN+vC9GRnhhpBx9o5uUbpKFVp177xX2/gZvgOCAfX9bQ6dzvU5k5My/CCT6YYYn2x4+hnFffyaz+MrJw= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux-foundation.org header.i=@linux-foundation.org header.b=ZmA3Ib3r; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux-foundation.org header.i=@linux-foundation.org header.b="ZmA3Ib3r" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 266231F000FF; Mon, 28 Sep 2026 21:51:07 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux-foundation.org; s=korg; t=1790632267; bh=9s/bCSRWs2bVgx1By72Nv5/r/MXPcdffsXegLKxI4dE=; h=Date:To:From:Subject; b=ZmA3Ib3rEKniLb2T9KzfIEtg7T3wjlAycUCCmzsMwA6QoAbEE9iwMQrhQXGC+arTc OEeXGf4+FBe9ovwaFF5wYr2nujeY3dlnd3tRw4gz7nap2f+WUS7eTweGi1T58i1vFw 8GFyqBBRN0nG0XWQG0ObPU27oSoW1uLOsrgR2ghA= Date: Mon, 28 Sep 2026 14:51:06 -0700 To: mm-commits@vger.kernel.org,kas@kernel.org,akpm@linux-foundation.org From: Andrew Morton Subject: [to-be-updated] mm-collapse-open-code-collapse_single_pmd-in-its-two-callers.patch removed from -mm tree Message-Id: <20260928215107.266231F000FF@smtp.kernel.org> Precedence: bulk X-Mailing-List: mm-commits@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: The quilt patch titled Subject: mm/collapse: open-code collapse_single_pmd() in its two callers has been removed from the -mm tree. Its filename was mm-collapse-open-code-collapse_single_pmd-in-its-two-callers.patch This patch was dropped because an updated version will be issued ------------------------------------------------------ From: "Kiryl Shutsemau (Meta)" Subject: mm/collapse: open-code collapse_single_pmd() in its two callers Date: Wed, 16 Sep 2026 10:31:36 +0100 collapse_scan_pmd() and collapse_run_pmd() each have a clear locking contract. The scan is called with mmap_lock held for reading and returns with it still held. The collapse is called without it. collapse_single_pmd() kept that boundary inside itself. It dropped the lock on some paths and not others, and reported which by way of a bool its callers had to carry along and then act on. Open-code it in the two callers. Each scans under the lock it already holds and, when the scan found work, gives the lock up before running the collapse. khugepaged's lock_dropped and madvise_collapse()'s mmap_unlocked both go: the code dropping the lock is now the code that wanted to know. khugepaged's walk carries on to the next table while the scan keeps refusing, and ends once a collapse has taken the lock from under it. madvise_collapse() re-finds its VMA after a collapse, which it did before, and now uses a NULL vma to say that it has to. It still reports the drop to its own caller, from the line that does it. The lock is given up and taken again at the same points as before. No functional change. Link: https://lore.kernel.org/20260916093145.4022188-10-kirill@shutemov.name Signed-off-by: Kiryl Shutsemau (Meta) Signed-off-by: Andrew Morton Reviewed-by: Zi Yan Reviewed-by: Baolin Wang Assisted-by: LLM Cc: Barry Song Cc: David Hildenbrand Cc: Dev Jain Cc: Jann Horn Cc: Lance Yang Cc: Liam R. Howlett Cc: Lorenzo Stoakes Cc: Ryan Roberts Cc: Vlastimil Babka --- mm/khugepaged.c | 103 ++++++++++++++++++++++------------------------ 1 file changed, 50 insertions(+), 53 deletions(-) --- a/mm/khugepaged.c~mm-collapse-open-code-collapse_single_pmd-in-its-two-callers +++ a/mm/khugepaged.c @@ -2869,28 +2869,6 @@ retract: return result; } -/* - * Try to collapse a single PMD starting at a PMD aligned addr, and return - * the results. - */ -static enum scan_result collapse_single_pmd(unsigned long addr, - struct vm_area_struct *vma, bool *lock_dropped, - struct collapse_control *cc) -{ - struct mm_struct *mm = vma->vm_mm; - enum scan_result result; - - result = collapse_scan_pmd(vma, addr, cc); - if (result != SCAN_SUCCEED && result != SCAN_PTE_MAPPED_HUGEPAGE) - return result; - - /* The collapse takes its own locks, so give this up */ - mmap_read_unlock(mm); - *lock_dropped = true; - - return collapse_run_pmd(mm, addr, result, cc); -} - static void collapse_scan_mm_slot(unsigned int progress_max, enum scan_result *result, struct collapse_control *cc) __releases(&khugepaged_mm_lock) @@ -2953,7 +2931,7 @@ static void collapse_scan_mm_slot(unsign VM_BUG_ON(khugepaged_scan.address & ~HPAGE_PMD_MASK); while (khugepaged_scan.address < hend) { - bool lock_dropped = false; + unsigned long addr; cond_resched(); if (unlikely(collapse_test_exit_or_disable(mm))) @@ -2963,23 +2941,30 @@ static void collapse_scan_mm_slot(unsign khugepaged_scan.address + HPAGE_PMD_SIZE > hend); - *result = collapse_single_pmd(khugepaged_scan.address, - vma, &lock_dropped, cc); - if (*result == SCAN_SUCCEED) - khugepaged_pages_collapsed++; + addr = khugepaged_scan.address; /* move to next address */ khugepaged_scan.address += HPAGE_PMD_SIZE; - if (lock_dropped) - /* - * We released mmap_lock so break loop. Note - * that we drop mmap_lock before all hugepage - * allocations, so if allocation fails, we are - * guaranteed to break here and report the - * correct result back to caller. - */ - goto breakouterloop_mmap_lock; - if (cc->progress >= progress_max) - goto breakouterloop; + + *result = collapse_scan_pmd(vma, addr, cc); + /* Nothing to do here, and the lock is still ours */ + if (*result != SCAN_SUCCEED && + *result != SCAN_PTE_MAPPED_HUGEPAGE) { + if (cc->progress >= progress_max) + goto breakouterloop; + continue; + } + + /* + * A collapse takes its own locks and is slow enough + * that a writer should not wait behind it, so give the + * lock up. That ends this walk: vma and the mm are + * whatever the collapse leaves them. + */ + mmap_read_unlock(mm); + *result = collapse_run_pmd(mm, addr, *result, cc); + if (*result == SCAN_SUCCEED) + khugepaged_pages_collapsed++; + goto breakouterloop_mmap_lock; } } breakouterloop: @@ -3248,7 +3233,6 @@ int madvise_collapse(struct vm_area_stru unsigned long hstart, hend, addr; enum scan_result last_fail = SCAN_FAIL; int thps = 0; - bool mmap_unlocked = false; BUG_ON(vma->vm_start > start); BUG_ON(vma->vm_end < end); @@ -3271,25 +3255,40 @@ int madvise_collapse(struct vm_area_stru lru_add_drain_all(); for (addr = hstart; addr < hend; addr += HPAGE_PMD_SIZE) { - enum scan_result result = SCAN_FAIL; + struct vm_area_struct *found; + enum scan_result result; - if (mmap_unlocked) { + /* + * A collapse gives the lock up, so the VMA has to be found + * again after one: it can shrink while nothing is held. A scan + * that finds nothing to collapse leaves the lock alone, so a + * range that is already collapsed walks on without relocking. + */ + if (!vma) { cond_resched(); mmap_read_lock(mm); - mmap_unlocked = false; - *lock_dropped = true; - result = hugepage_vma_revalidate(mm, addr, false, &vma, + result = hugepage_vma_revalidate(mm, addr, false, &found, cc, HPAGE_PMD_ORDER); if (result != SCAN_SUCCEED) { last_fail = result; - goto out_nolock; + goto out_locked; } - + vma = found; hend = min(hend, vma->vm_end & HPAGE_PMD_MASK); } - result = collapse_single_pmd(addr, vma, &mmap_unlocked, cc); + result = collapse_scan_pmd(vma, addr, cc); + /* Nothing to do here, and the lock is still ours */ + if (result != SCAN_SUCCEED && result != SCAN_PTE_MAPPED_HUGEPAGE) + goto tally; + + /* The collapse takes its own locks, so give this up */ + mmap_read_unlock(mm); + *lock_dropped = true; + vma = NULL; + result = collapse_run_pmd(mm, addr, result, cc); +tally: switch (result) { case SCAN_SUCCEED: case SCAN_PMD_MAPPED: @@ -3311,17 +3310,15 @@ int madvise_collapse(struct vm_area_stru default: last_fail = result; /* Other error, exit */ - goto out_maybelock; + goto out; } } -out_maybelock: +out: /* Caller expects us to hold mmap_lock on return */ - if (mmap_unlocked) { - *lock_dropped = true; + if (!vma) mmap_read_lock(mm); - } -out_nolock: +out_locked: mmap_assert_locked(mm); collapse_control_release(cc); kfree(cc); _ Patches currently in -mm which might be from kas@kernel.org are mm-huge_memory-do-not-touch-frozen-folios-in-deferred_split_isolate.patch mm-huge_memory-dequeue-the-deferred-split-after-the-split-freeze.patch mm-huge_memory-add-folio_reset_partially_mapped.patch mm-collapse-work-out-the-orders-a-vma-allows-once-per-vma.patch mm-collapse-declare-the-collapse-interface-in-collapseh.patch mm-collapse-implement-madv_collapse-in-madvisec.patch selftests-mm-raise-the-khugepaged-test-case-cap.patch selftests-mm-skip-collapse_compound_extreme-where-the-pmd-is-too-large.patch selftests-mm-scale-khugepageds-collapse-wait-with-the-pmd-size.patch selftests-mm-skip-khugepaged-page-cache-cases-without-a-pmd-folio.patch selftests-mm-make-the-swap-cases-swapout-reliable.patch selftests-mm-stop-khugepaged-during-the-madv_collapse-cases.patch selftests-mm-move-is_backed_by_folio-into-vm_util.patch selftests-mm-add-folio-order-check-for-address-ranges.patch selftests-mm-add-folio-order-detection-self-check.patch selftests-mm-add-khugepaged-completion-barrier-helper.patch selftests-mm-add-order-parameterized-khugepaged-collapse-cases.patch selftests-mm-parameterize-the-mixed-source-collapse-case-by-source-order.patch selftests-mm-cover-a-shared-source-collapse-write-race.patch selftests-mm-run-every-supported-collapse-order-by-default.patch selftests-mm-check-that-one-khugepaged-pass-collapses-one-window.patch selftests-mm-add-khugepaged-race-harness.patch selftests-mm-race-the-collapse-of-windows-with-holes.patch selftests-mm-add-memory-pressure-threads-to-the-khugepaged-race-harness.patch selftests-mm-zap-whole-pte-tables-in-the-khugepaged-race-harness.patch