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 A541C502568 for ; Mon, 28 Sep 2026 22:01:38 +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=1790632900; cv=none; b=iqNGkR0Q7X1Ufcj8OIpBQRGm35XqXAFTXm4tadHIeLhH/X4Kz9gnWzCyum1qUD/+/hs6nbI3IMlsnaJVKTxxWexuvemh0p8FOxUDuM3Sa5lQPcMgxwHuZwbVUArQ4zf6fMnfYJ9shfmLSQLXjRVGE7fY0VZMJSkO/Lvw9EPyCRo= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790632900; c=relaxed/simple; bh=gFlRBoN4QC3EZQ/cQJfxeG9/1TNHmCh97ntXI0RqHmk=; h=Date:To:From:Subject:Message-Id; b=LjONwUngbhS+8PnCQzoVocOlWLD6OyujJ2GhgTYD5ZUMkk1eCmR4LdMhqSmQ7lBDPVUVdqH8NQMC9jIY0nNNra/7VVRjUP6rCh+dwuHPPbBc40N/7QejZHHS7YZrqc+UikuqWJ8cs/3Imp1MftqWoEMP5iucqrUYHGiB5lHqCKU= 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=wb4A0rJD; 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="wb4A0rJD" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 52FD51F000FF; Mon, 28 Sep 2026 22:01:38 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux-foundation.org; s=korg; t=1790632898; bh=IR0oIijjFKX4IizNNTWc+HvyvJC3Ck5pa7gnFe2lpo0=; h=Date:To:From:Subject; b=wb4A0rJDbH+XbmKQ20+bByoX86nXFTHtWz7ZFN2IW70hcQgYVyIkkP6AMEAUyMqaI JvjFP2T9FMEIcxwudKd9sjvRNWSn5RQcEhdLOD1ovPbi/kBIToyKcxAhZzZB7ehCo2 1VwtkT3vPftZ/0yV6z88fxo46tx5Q+8d0CirSWRY= Date: Mon, 28 Sep 2026 15:01:37 -0700 To: mm-commits@vger.kernel.org,kas@kernel.org,akpm@linux-foundation.org From: Andrew Morton Subject: + mm-collapse-state-what-a-collapse-may-do-in-the-policy.patch added to mm-unstable branch Message-Id: <20260928220138.52FD51F000FF@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: state what a collapse may do in the policy has been added to the -mm mm-unstable branch. Its filename is mm-collapse-state-what-a-collapse-may-do-in-the-policy.patch This patch will shortly appear at https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-collapse-state-what-a-collapse-may-do-in-the-policy.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: state what a collapse may do in the policy Date: Mon, 28 Sep 2026 11:06:19 +0100 Tests scattered through the collapse path decide what a collapse is allowed to do by asking whether khugepaged started it. Between them they settle: - which VMAs are eligible, and how hard to try for a folio; - how many empty, swapped-out or shared PTEs a window may contain, and whether a sub-PMD window is held to a stricter rule than a PMD; - whether a range has to look used, and whether a MADV_FREE'd page is left alone; - whether the PMD is mapped as part of the request, and whether dirty pages are worth writing back and retrying. None of those is a fact about khugepaged. Each is something the caller decided before asking, and the collapse code should not have to look up who called to find out. Add struct collapse_policy for the caller to fill: khugepaged from its own settings, MADV_COLLAPSE from the fact that a user asked explicitly. Every test becomes a read of a field, and cc->is_khugepaged goes, having no reader left. The PTE limits come as two sets, one for a PMD-sized window and one for anything smaller, so that the helpers pick a set for the order and read it. khugepaged takes no swapped-out or shared PTE into a sub-PMD window, and empty PTEs only when the knob says all or nothing; the warning for a knob value in between moves to where khugepaged fills its policy. The fields only one side reads say which: anon_ or file_. David Hildenbrand asked for both. khugepaged fills the policy once per scan pass, MADV_COLLAPSE once per call. That is the one change in behaviour. The max_ptes_* limits and the defrag setting behind the allocation mask are sampled once per pass rather than on every table. A table scanned early in a pass and one scanned late are then treated alike. collapse_file() also drops a NULL check on the collapse_control. It has one call site, reached only from collapse_single_pmd(), which dereferences cc unconditionally, so the check was already dead. Link: https://lore.kernel.org/20260928100630.21870-6-kirill@shutemov.name Signed-off-by: Kiryl Shutsemau (Meta) Signed-off-by: Andrew Morton Acked-by: David Hildenbrand (Arm) Assisted-by: LLM Cc: Lorenzo Stoakes Cc: Zi Yan Cc: Baolin Wang 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/collapse.h | 41 ++++++++++++ mm/khugepaged.c | 147 ++++++++++++++++++++++++---------------------- 2 files changed, 118 insertions(+), 70 deletions(-) --- a/mm/collapse.h~mm-collapse-state-what-a-collapse-may-do-in-the-policy +++ a/mm/collapse.h @@ -45,8 +45,47 @@ enum scan_result { SCAN_PAGE_DIRTY_OR_WRITEBACK, }; +/* How many PTEs of a window may be missing, swapped out or shared */ +struct collapse_limits { + /* Counted over a PMD-sized window; HPAGE_PMD_NR means "no limit" */ + unsigned int max_ptes_none; + unsigned int max_ptes_swap; + unsigned int max_ptes_shared; +}; + +/* What a collapse is allowed to do, decided by the caller that asks for it */ +struct collapse_policy { + /* Limits for a PMD-sized window */ + struct collapse_limits pmd; + + /* + * Limits for a smaller window. Its max_ptes_none is either 0 or + * COLLAPSE_MAX_PTES_LIMIT, the latter meaning all but one PTE of the + * window whatever its order; any other value counts as 0. + */ + struct collapse_limits sub_pmd; + + /* Leave clean lazyfree folios to reclaim rather than collapse them */ + bool anon_skip_lazyfree; + + /* Refuse an anonymous range with no sign of use */ + bool anon_require_referenced; + + /* Map the PMD over a file collapse instead of leaving it to a fault */ + bool file_install_pmd; + + /* Write dirty pages back and retry once instead of refusing them */ + bool file_writeback_dirty; + + /* How hard to try for a destination folio */ + gfp_t gfp; + + /* Which VMAs are eligible, as thp_vma_allowable_orders() spells it */ + enum tva_type tva_type; +}; + struct collapse_control { - bool is_khugepaged; + struct collapse_policy policy; /* Num pages scanned per node */ u32 node_load[MAX_NUMNODES]; --- a/mm/khugepaged.c~mm-collapse-state-what-a-collapse-may-do-in-the-policy +++ a/mm/khugepaged.c @@ -314,30 +314,17 @@ static bool pte_none_or_zero(pte_t pte) static unsigned int collapse_max_ptes_none(struct collapse_control *cc, struct vm_area_struct *vma, unsigned int order) { - const unsigned int max_ptes_none = khugepaged_max_ptes_none; + unsigned int max_ptes_none; if (vma && userfaultfd_armed(vma)) return 0; - /* for MADV_COLLAPSE, allow any empty/shared zeropage PTEs */ - if (!cc->is_khugepaged) - return HPAGE_PMD_NR; - /* for PMD collapse, respect the user defined maximum */ if (is_pmd_order(order)) - return max_ptes_none; - /* - * for mTHP collapse with the sysctl value set to COLLAPSE_MAX_PTES_LIMIT, - * scale the maximum number of PTEs to the order of the collapse. - */ + return cc->policy.pmd.max_ptes_none; + + /* Below PMD order: all but one PTE of the window, or none */ + max_ptes_none = cc->policy.sub_pmd.max_ptes_none; if (max_ptes_none == COLLAPSE_MAX_PTES_LIMIT) return (1 << order) - 1; - /* - * For mTHP collapse of values other than 0 or COLLAPSE_MAX_PTES_LIMIT, - * emit a warning and return 0. - */ - if (max_ptes_none) - pr_warn_once("mTHP collapse does not support max_ptes_none" - " values other than 0 or %u, defaulting to 0.\n", - COLLAPSE_MAX_PTES_LIMIT); return 0; } @@ -353,20 +340,9 @@ static unsigned int collapse_max_ptes_no static unsigned int collapse_max_ptes_shared(struct collapse_control *cc, unsigned int order) { - /* - * For MADV_COLLAPSE, do not restrict the number of PTEs that map shared - * anonymous pages. - */ - if (!cc->is_khugepaged) - return HPAGE_PMD_NR; - /* - * for mTHP collapse do not allow collapsing anonymous memory pages that - * are shared between processes. - */ - if (!is_pmd_order(order)) - return 0; - /* for PMD collapse, respect the user defined maximum */ - return khugepaged_max_ptes_shared; + if (is_pmd_order(order)) + return cc->policy.pmd.max_ptes_shared; + return cc->policy.sub_pmd.max_ptes_shared; } /** @@ -381,17 +357,9 @@ static unsigned int collapse_max_ptes_sh static unsigned int collapse_max_ptes_swap(struct collapse_control *cc, unsigned int order) { - /* - * For MADV_COLLAPSE, do not restrict the number PTEs entries or - * pagecache entries that are non-present. - */ - if (!cc->is_khugepaged) - return HPAGE_PMD_NR; - /* for mTHP collapse do not allow any non-present PTEs or pagecache entries */ - if (!is_pmd_order(order)) - return 0; - /* for PMD collapse, respect the user defined maximum */ - return khugepaged_max_ptes_swap; + if (is_pmd_order(order)) + return cc->policy.pmd.max_ptes_swap; + return cc->policy.sub_pmd.max_ptes_swap; } int hugepage_madvise(struct vm_area_struct *vma, @@ -678,7 +646,7 @@ static enum scan_result __collapse_huge_ * If the vma has the VM_DROPPABLE flag, the collapse will * preserve the lazyfree property without needing to skip. */ - if (cc->is_khugepaged && !(vma->vm_flags & VM_DROPPABLE) && + if (cc->policy.anon_skip_lazyfree && !(vma->vm_flags & VM_DROPPABLE) && folio_test_lazyfree(folio) && !pte_dirty(pteval)) { result = SCAN_PAGE_LAZYFREE; goto out; @@ -767,12 +735,12 @@ static enum scan_result __collapse_huge_ if (folio_test_large(folio)) list_add_tail(&folio->lru, compound_pagelist); next: - if (cc->is_khugepaged && + if (cc->policy.anon_require_referenced && folio_pte_referenced(folio, vma, addr, pteval)) referenced++; } - if (unlikely(cc->is_khugepaged && !referenced)) { + if (unlikely(cc->policy.anon_require_referenced && !referenced)) { result = SCAN_LACK_REFERENCED_PAGE; } else { result = SCAN_SUCCEED; @@ -938,9 +906,7 @@ static void khugepaged_alloc_sleep(void) remove_wait_queue(&khugepaged_wait, &wait); } -static struct collapse_control khugepaged_collapse_control = { - .is_khugepaged = true, -}; +static struct collapse_control khugepaged_collapse_control; static bool collapse_scan_abort(int nid, struct collapse_control *cc) { @@ -976,6 +942,52 @@ static inline gfp_t alloc_hugepage_khuge return khugepaged_defrag() ? GFP_TRANSHUGE : GFP_TRANSHUGE_LIGHT; } +/* khugepaged collapses on its own initiative, so it obeys its own settings */ +static void collapse_policy_khugepaged(struct collapse_policy *p) +{ + p->pmd.max_ptes_none = READ_ONCE(khugepaged_max_ptes_none); + p->pmd.max_ptes_swap = READ_ONCE(khugepaged_max_ptes_swap); + p->pmd.max_ptes_shared = READ_ONCE(khugepaged_max_ptes_shared); + + /* + * A sub-PMD window takes no swapped-out and no shared PTE: reading + * pages back or breaking CoW is not worth it for an mTHP. Empty PTEs + * it takes all or nothing, since anything in between would let one + * collapse feed the next. + */ + p->sub_pmd.max_ptes_none = p->pmd.max_ptes_none; + if (p->sub_pmd.max_ptes_none && + p->sub_pmd.max_ptes_none != COLLAPSE_MAX_PTES_LIMIT) + pr_warn_once("mTHP collapse does not support max_ptes_none values other than 0 or %u, defaulting to 0.\n", + COLLAPSE_MAX_PTES_LIMIT); + p->sub_pmd.max_ptes_swap = 0; + p->sub_pmd.max_ptes_shared = 0; + + p->anon_skip_lazyfree = true; + p->anon_require_referenced = true; + p->file_install_pmd = false; + p->file_writeback_dirty = false; + p->gfp = alloc_hugepage_khugepaged_gfpmask(); + p->tva_type = TVA_KHUGEPAGED; +} + +/* MADV_COLLAPSE was asked for explicitly, so it is not held to those */ +static void collapse_policy_madvise(struct collapse_policy *p) +{ + p->pmd.max_ptes_none = HPAGE_PMD_NR; + p->pmd.max_ptes_swap = HPAGE_PMD_NR; + p->pmd.max_ptes_shared = HPAGE_PMD_NR; + /* Never read: MADV_COLLAPSE collapses to PMD order only */ + p->sub_pmd = p->pmd; + + p->anon_skip_lazyfree = false; + p->anon_require_referenced = false; + p->file_install_pmd = true; + p->file_writeback_dirty = true; + p->gfp = GFP_TRANSHUGE; + p->tva_type = TVA_FORCED_COLLAPSE; +} + #ifdef CONFIG_NUMA static int collapse_find_target_node(struct collapse_control *cc) { @@ -1013,8 +1025,7 @@ static enum scan_result hugepage_vma_rev struct collapse_control *cc, unsigned int order) { struct vm_area_struct *vma; - enum tva_type type = cc->is_khugepaged ? TVA_KHUGEPAGED : - TVA_FORCED_COLLAPSE; + enum tva_type type = cc->policy.tva_type; if (unlikely(collapse_test_exit_or_disable(mm))) return SCAN_ANY_PROCESS; @@ -1197,8 +1208,7 @@ out: static enum scan_result alloc_charge_folio(struct folio **foliop, struct mm_struct *mm, struct collapse_control *cc, unsigned int order) { - gfp_t gfp = (cc->is_khugepaged ? alloc_hugepage_khugepaged_gfpmask() : - GFP_TRANSHUGE); + gfp_t gfp = cc->policy.gfp; int node = collapse_find_target_node(cc); struct folio *folio; @@ -1581,7 +1591,7 @@ static enum scan_result collapse_scan_pm const unsigned int max_ptes_shared = collapse_max_ptes_shared(cc, HPAGE_PMD_ORDER); const unsigned int max_ptes_swap = collapse_max_ptes_swap(cc, HPAGE_PMD_ORDER); unsigned int max_ptes_none = collapse_max_ptes_none(cc, vma, HPAGE_PMD_ORDER); - enum tva_type tva_flags = cc->is_khugepaged ? TVA_KHUGEPAGED : TVA_FORCED_COLLAPSE; + enum tva_type tva_flags = cc->policy.tva_type; pmd_t *pmd; pte_t *pte, *_pte, pteval; int i; @@ -1681,7 +1691,7 @@ static enum scan_result collapse_scan_pm * If the vma has the VM_DROPPABLE flag, the collapse will * preserve the lazyfree property without needing to skip. */ - if (cc->is_khugepaged && !(vma->vm_flags & VM_DROPPABLE) && + if (cc->policy.anon_skip_lazyfree && !(vma->vm_flags & VM_DROPPABLE) && folio_test_lazyfree(folio) && !pte_dirty(pteval)) { result = SCAN_PAGE_LAZYFREE; failed_pfn = folio_pfn(folio); @@ -1747,13 +1757,13 @@ static enum scan_result collapse_scan_pm goto out_unmap; } - if (cc->is_khugepaged && + if (cc->policy.anon_require_referenced && folio_pte_referenced(folio, vma, addr, pteval)) referenced++; } - if (cc->is_khugepaged && - (!referenced || - (unmapped && referenced < HPAGE_PMD_NR / 2))) { + if (cc->policy.anon_require_referenced && + (!referenced || + (unmapped && referenced < HPAGE_PMD_NR / 2))) { result = SCAN_LACK_REFERENCED_PAGE; } else { result = SCAN_SUCCEED; @@ -2605,11 +2615,11 @@ immap_locked: xas_unlock_irq(&xas); /* - * Remove pte page tables, so we can re-fault the page as huge. - * If MADV_COLLAPSE, adjust result to call try_collapse_pte_mapped_thp(). + * Remove pte page tables, so we can re-fault the page as huge. A + * caller that wants the PMD mapped now is told to go and do that. */ retract_page_tables(mapping, start); - if (cc && !cc->is_khugepaged) + if (cc->policy.file_install_pmd) result = SCAN_PTE_MAPPED_HUGEPAGE; folio_unlock(new_folio); @@ -2796,11 +2806,8 @@ static enum scan_result collapse_single_ retry: result = collapse_scan_file(mm, addr, file, pgoff, cc); - /* - * For MADV_COLLAPSE, when encountering dirty pages, try to writeback, - * then retry the collapse one time. - */ - if (!cc->is_khugepaged && result == SCAN_PAGE_DIRTY_OR_WRITEBACK && + /* Dirty pages are worth a writeback and one more try, if asked for */ + if (cc->policy.file_writeback_dirty && result == SCAN_PAGE_DIRTY_OR_WRITEBACK && !triggered_wb && mapping_can_writeback(file->f_mapping)) { const loff_t lstart = (loff_t)pgoff << PAGE_SHIFT; const loff_t lend = lstart + HPAGE_PMD_SIZE - 1; @@ -2817,7 +2824,7 @@ retry: result = SCAN_ANY_PROCESS; else result = try_collapse_pte_mapped_thp(mm, addr, - !cc->is_khugepaged); + cc->policy.file_install_pmd); if (result == SCAN_PMD_MAPPED) result = SCAN_SUCCEED; mmap_read_unlock(mm); @@ -2966,6 +2973,8 @@ static void khugepaged_do_scan(struct co lru_add_drain_all(); + collapse_policy_khugepaged(&cc->policy); + cc->progress = 0; while (true) { cond_resched(); @@ -3193,7 +3202,7 @@ int madvise_collapse(struct vm_area_stru cc = kmalloc_obj(*cc); if (!cc) return -ENOMEM; - cc->is_khugepaged = false; + collapse_policy_madvise(&cc->policy); cc->progress = 0; lru_add_drain_all(); _ 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