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 D314D49B5CF for ; Thu, 10 Sep 2026 21:56:10 +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=1789077372; cv=none; b=uMBo1yP/VdtPCNmqXnS2PfTo0zAo/QY2ICjlyBf0vOo76RstrfXiRuqqltgJt8pE5VKiKsjfZb4AhFp1Uyyx49wnUOcvdcTLngfuHvV+BoLtT7OvP97reIi73A60MlprCefSZAs0dNMTbkByB2m/omoHzAy+Ca7EQ0IDl+H0+Z4= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789077372; c=relaxed/simple; bh=XZh32cA5wXnUiEy/V+JaS4vbuAAypXy99Bdx7+vFolw=; h=Date:To:From:Subject:Message-Id; b=RnS6xvdMX1C6ohXIEAu61Y+KjIkYTbwvnHYqpWE34GnEn+G6TKYzoLG1MkzLLb59Hcw/SlNCOs82Jm3uulKkLRbimW9IYfzSztZy+yLTPdcsf7KWjYjnuBbKfRjLo+DlCEtbujXN6+NHTuHe0KhqZ/NNdgk0sNXG9JhrmQeJKmc= 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=KIpswya8; 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="KIpswya8" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 8A9131F000FF; Thu, 10 Sep 2026 21:56:10 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux-foundation.org; s=korg; t=1789077370; bh=Y/iy9wCDpibTGqW4sAhDxfVqHYw28QQYrfZyie9/khU=; h=Date:To:From:Subject; b=KIpswya88mycfciFnyk3FNvgCWTTJg/1ezv/sXTgJfFWcxrpAc7fd/+HsgzFQeRTx 05ket3/6kDCOegjjgVQZPvFWKRJ1UwkZXDQ7B6zT4egZC3JyVpxyr4uS2iVhfIVA3S RY6E7qqEKNVbzUADfhpwSci0MH7QJxIg+j9s7CJE= Date: Thu, 10 Sep 2026 14:56:10 -0700 To: mm-commits@vger.kernel.org,ziy@nvidia.com,vbabka@kernel.org,ryan.roberts@arm.com,ljs@kernel.org,liam@infradead.org,lance.yang@linux.dev,jannh@google.com,dev.jain@arm.com,david@kernel.org,baolin.wang@linux.alibaba.com,baohua@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-new branch Message-Id: <20260910215610.8A9131F000FF@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-new 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-new branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm Note, mm-new is a provisional staging ground for work-in-progress patches, and acceptance into mm-new is a notification for others take notice and to finish up reviews. Please do not hesitate to respond to review feedback and post updated versions to replace or incrementally fixup patches in mm-new. The mm-new branch of mm.git is not included in linux-next If a few days of testing in mm-new is successful, the patch will me moved into mm.git's mm-unstable branch, which is included in linux-next 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: Thu, 10 Sep 2026 13:02:29 +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, on SCAN_SUCCEED, 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. Assisted-by: LLM Link: https://lore.kernel.org/20260910120238.2529819-10-kirill@shutemov.name Signed-off-by: Kiryl Shutsemau (Meta) Cc: Baolin Wang 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 Cc: Zi Yan Signed-off-by: Andrew Morton --- mm/khugepaged.c | 102 ++++++++++++++++++++++------------------------ 1 file changed, 49 insertions(+), 53 deletions(-) --- a/mm/khugepaged.c~mm-collapse-open-code-collapse_single_pmd-in-its-two-callers +++ a/mm/khugepaged.c @@ -2857,28 +2857,6 @@ 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) - 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, cc); -} - static void collapse_scan_mm_slot(unsigned int progress_max, enum scan_result *result, struct collapse_control *cc) __releases(&khugepaged_mm_lock) @@ -2941,7 +2919,7 @@ 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))) @@ -2951,23 +2929,29 @@ 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 collapse here, and the lock is still ours */ + if (*result != SCAN_SUCCEED) { + 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, cc); + if (*result == SCAN_SUCCEED) + khugepaged_pages_collapsed++; + goto breakouterloop_mmap_lock; } } breakouterloop: @@ -3236,7 +3220,6 @@ 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); @@ -3259,25 +3242,40 @@ 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 collapse here, and the lock is still ours */ + if (result != SCAN_SUCCEED) + 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, cc); +tally: switch (result) { case SCAN_SUCCEED: case SCAN_PMD_MAPPED: @@ -3299,17 +3297,15 @@ 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-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-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