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 2E77250276E for ; Mon, 28 Sep 2026 22:01:50 +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=1790632913; cv=none; b=J0uYE0MiCVzmYoP12mTxi4qSfl5WXhEC8IoS8Hl9u19pHFq3jw0dmFJ6UBh855LmCVOuDH6IaRZP5vf2L6s3gczW3xLyn4f5BZe4pjF1kdNn3JzpsQIPbXScWz2J+j+4KXMJFc0jn7172RbGAUXWoyvWW6dP02EmtJTalXUjDYo= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790632913; c=relaxed/simple; bh=twqBBwIRHj21qN/WsqUqLQojFMjFMKAtU7i60N72pWQ=; h=Date:To:From:Subject:Message-Id; b=nRj8WXgNYdDJ2bu0NVFDV49htLY/U1ghaHx7crcYiLmZAaoIbKcl3WW/QTxkMqEH3o/P7LrASgTMlDjHwU4uV8Vin7G7FnLHe+ozegOOOBMA6TPlaR94UhjYoLjGvoIpnHROMohdvcSOoPL4BnekdItcpXFWCA49T6qREXXIeLs= 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=Zzb/ZxRU; 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="Zzb/ZxRU" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 1A3D91F000FF; Mon, 28 Sep 2026 22:01:49 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux-foundation.org; s=korg; t=1790632909; bh=vpjXMwiilFref3IIpUIn/CEjJb86WKnyaOWoNtLwziY=; h=Date:To:From:Subject; b=Zzb/ZxRUBKVo95zW1TFV3rlHsnl/ku9eIe7KYnZYABQ3LDoMge4pkXSGMLUqn4pLY EAHwMrIDrB6R0YgHDNTGUvD5gkqulGIcJAiq60p5+6gdsCYwDHKe0mC6Ej9Ralggxz 8XYvmo3tPYxW7rckQy7kCwqMHVOwGD16UuLJ/rT0= Date: Mon, 28 Sep 2026 15:01:48 -0700 To: mm-commits@vger.kernel.org,kas@kernel.org,akpm@linux-foundation.org From: Andrew Morton Subject: + mm-collapse-open-code-collapse_single_pmd-in-its-two-callers.patch added to mm-unstable branch Message-Id: <20260928220149.1A3D91F000FF@smtp.kernel.org> Precedence: bulk X-Mailing-List: mm-commits@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: The patch titled Subject: mm/collapse: open-code collapse_single_pmd() in its two callers has been added to the -mm mm-unstable branch. Its filename is mm-collapse-open-code-collapse_single_pmd-in-its-two-callers.patch This patch will shortly appear at https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-collapse-open-code-collapse_single_pmd-in-its-two-callers.patch This patch will later appear in the mm-unstable branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm Before you just go and hit "reply", please: a) Consider who else should be cc'ed b) Prefer to cc a suitable mailing list as well c) Ideally: find the original patch on the mailing list and do a reply-to-all to that, adding suitable additional cc's *** Remember to use Documentation/process/submit-checklist.rst when testing your code *** The -mm tree is included into linux-next via various branches at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm and is updated there most days ------------------------------------------------------ From: "Kiryl Shutsemau (Meta)" Subject: mm/collapse: open-code collapse_single_pmd() in its two callers Date: Mon, 28 Sep 2026 11:06:24 +0100 A scan and a collapse want different things from mmap_lock. The scan reads one PTE table under the lock the caller holds, refuses most of the time, and the caller moves on to the next table without letting go. The collapse allocates, may sleep in writeback and takes the lock for write itself, so the lock it is handed is of no use to 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. Both callers already act on a drop, khugepaged by ending its walk and madvise_collapse() by looking its VMA up again. The code that has to know is not the code that does it. 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. The scan then has one rule, called locked and returning locked, and the run another, called unlocked. Nothing is left to report, so khugepaged's lock_dropped and madvise_collapse()'s mmap_unlocked both go. The engine never touches a lock it did not take, and how a caller locks its scan is the caller's business alone. 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. Preparation for moving madvise_collapse() out of khugepaged.c: what it needs from the engine is then two calls with one lock rule each. The lock is given up and taken again at the same points as before. No functional change. Link: https://lore.kernel.org/20260928100630.21870-11-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: David Hildenbrand Cc: Lorenzo Stoakes Cc: Liam R. Howlett Cc: Nico Pache Cc: Ryan Roberts Cc: Dev Jain Cc: Barry Song Cc: Lance Yang Cc: Usama Arif Cc: Vlastimil Babka Cc: Jann Horn --- 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 @@ -2856,28 +2856,6 @@ put: 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) @@ -2940,7 +2918,7 @@ 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))) @@ -2950,23 +2928,30 @@ 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: @@ -3232,7 +3217,6 @@ 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); @@ -3255,25 +3239,40 @@ 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: @@ -3295,17 +3294,15 @@ 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); 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-khugepaged-drop-redundant-mm_struct-pin-in-madvise_collapse.patch mm-khugepaged-count-collapses-where-khugepaged-makes-them.patch mm-khugepaged-rename-mthp_present_ptes-bitmap-to-eligible_ptes.patch mm-collapse-add-collapseh-for-the-collapse-interface.patch mm-collapse-state-what-a-collapse-may-do-in-the-policy.patch mm-collapse-drop-the-collapse_possible-wrapper.patch mm-collapse-name-the-per-table-scan-reset-for-what-it-resets.patch mm-collapse-call-collapse_file-from-collapse_single_pmd.patch mm-collapse-separate-scanning-a-pte-table-from-collapsing-it.patch mm-collapse-open-code-collapse_single_pmd-in-its-two-callers.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