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 ED5E14FD7B2 for ; Mon, 28 Sep 2026 22:01:29 +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=1790632891; cv=none; b=Lu4eTaL1IWE2HBwH9S3XvQoqZOqlN360ADIXLCE2KvWrllXgJRWzl2FDuKbI8vxESHJKItU7tDutQsiBBvj+3X6t8oHiwMibEDJmrA4vXRmQLYrJ0syIfHSnz/sirAYuZ5wG0fihieHuil9wRjHAS/I+UuLAhtWSCBKNUmReXxo= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790632891; c=relaxed/simple; bh=FsxLGP0pwHTrKghbxmBbq12PI6trDIDs3BrUHzichw8=; h=Date:To:From:Subject:Message-Id; b=kCSRQXKX+49vOFvRlhLhR098cU4PJt5l/ouDkh6aI/yQ0VYRTKBl/SwYF94fPPw+B8+Hu4ELr2W+km8vgq15tLSvMAXBc+cfnBuX1DxfCdCjqWBNrq8M4HE5ofo+EAGCzrOT4YCYpSwIKmTctLkb7pXvfcgdayhrCtU9xR/RyxQ= 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=qoTlLHAy; 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="qoTlLHAy" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 84F9E1F00893; Mon, 28 Sep 2026 22:01:29 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux-foundation.org; s=korg; t=1790632889; bh=jrggkU4bB7VdL1KxNt78LANI53VR/FUChni2gHAgPCs=; h=Date:To:From:Subject; b=qoTlLHAydOBwBLy7SKd2PjmgvHEryN6vz05QX7i96B6U4kW5DnQ70nFAzDRDK/gEO Kh8s0NOAuxuHJOSWcoeWcvJNd+W0F74+sxHh3BjQj4mDsPSaKHLgonSHpiFV2HoBcw 7cb7ysBwaEELt7OC0bb47Pg5QrvtnIG309ahzWTg= Date: Mon, 28 Sep 2026 15:01:29 -0700 To: mm-commits@vger.kernel.org,kas@kernel.org,akpm@linux-foundation.org From: Andrew Morton Subject: + mm-khugepaged-drop-redundant-mm_struct-pin-in-madvise_collapse.patch added to mm-unstable branch Message-Id: <20260928220129.84F9E1F00893@smtp.kernel.org> Precedence: bulk X-Mailing-List: mm-commits@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: The patch titled Subject: mm/khugepaged: drop redundant mm_struct pin in madvise_collapse() has been added to the -mm mm-unstable branch. Its filename is mm-khugepaged-drop-redundant-mm_struct-pin-in-madvise_collapse.patch This patch will shortly appear at https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-khugepaged-drop-redundant-mm_struct-pin-in-madvise_collapse.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/khugepaged: drop redundant mm_struct pin in madvise_collapse() Date: Mon, 28 Sep 2026 11:06:15 +0100 Patch series "mm/collapse: separate a collapse from its callers", v4. There is no line between the collapse engine and the callers that ask for a collapse. khugepaged.c holds both, and they reach into each other. - Sixteen tests through the collapse path read cc->is_khugepaged to work out what they are allowed to do, when every one of those decisions was made by the caller before it asked. - collapse_single_pmd() does both halves of a collapse behind one call and drops mmap_lock somewhere in the middle. Which of its paths dropped it is not something a caller can see, so it hands back a bool and the caller keeps track. - MADV_COLLAPSE's implementation -- the walk over the user's range, the per-PMD loop, the errno translation -- sits in khugepaged.c, which is the daemon's file. So: draw the line. State what a caller allows in a policy, split the call in two with the lock as the boundary, and move the syscall to madvise.c. What the engine offers is then three calls, with the lock state written down against each, and a policy the caller fills for itself: collapse_control_init(cc) once, before the first table collapse_policy_*(&cc->policy) what this caller allows collapse_scan_pmd(vma, addr, ...) per table, under mmap_lock collapse_run_pmd(mm, addr, ...) when a scan found work, no mmap_lock The engine stays in khugepaged.c for now; what changes is that it has an interface, and that neither half has to ask about the other. madvise.c gains the operation it should have had all along. This patch (of 13): madvise_collapse() holds an mmgrab() reference across its work. It is redundant. Every caller already holds mm_users: - madvise(2) works on current->mm, which lives as long as the task is in the syscall; - process_madvise(2) reaches a remote mm through mm_access(), which takes an mm_users reference and holds it until the syscall returns; - io_uring passes current->mm; - DAMON takes one with get_task_mm() and drops it after the call. Drop the mmgrab()/mmdrop() pair. Link: https://lore.kernel.org/20260928100630.21870-1-kirill@shutemov.name Link: https://lore.kernel.org/20260928100630.21870-2-kirill@shutemov.name Signed-off-by: Kiryl Shutsemau (Meta) Signed-off-by: Andrew Morton Acked-by: David Hildenbrand (Arm) Reviewed-by: Zi Yan Reviewed-by: Baolin Wang Assisted-by: LLM 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 | 2 -- 1 file changed, 2 deletions(-) --- a/mm/khugepaged.c~mm-khugepaged-drop-redundant-mm_struct-pin-in-madvise_collapse +++ a/mm/khugepaged.c @@ -3252,7 +3252,6 @@ int madvise_collapse(struct vm_area_stru cc->is_khugepaged = false; cc->progress = 0; - mmgrab(mm); lru_add_drain_all(); for (addr = hstart; addr < hend; addr += HPAGE_PMD_SIZE) { @@ -3308,7 +3307,6 @@ out_maybelock: } out_nolock: mmap_assert_locked(mm); - mmdrop(mm); kfree(cc); return thps == ((hend - hstart) >> HPAGE_PMD_SHIFT) ? 0 _ 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