+ mm-collapse-implement-madv_collapse-in-madvisec.patch added to mm-new branch

[Andrew Morton <akpm@linux-foundation.org>]

The patch titled
     Subject: mm/collapse: implement MADV_COLLAPSE in madvise.c
has been added to the -mm mm-new branch.  Its filename is
     mm-collapse-implement-madv_collapse-in-madvisec.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-collapse-implement-madv_collapse-in-madvisec.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

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*** Remember to use Documentation/process/submit-checklist.rst when testing your code ***

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------------------------------------------------------
From: "Kiryl Shutsemau (Meta)" <kas@kernel.org>
Subject: mm/collapse: implement MADV_COLLAPSE in madvise.c
Date: Thu, 10 Sep 2026 13:02:32 +0100

MADV_COLLAPSE is a madvise operation, but its implementation sat in
khugepaged.c.  The daemon's file therefore also held a syscall's worth of
code that has nothing to do with the daemon: the walk over the user's
range, the per-PMD loop, and the errno translation.

Move it to madvise.c, among the operations it belongs with, along with the
errno map and the policy it states for itself.  It takes a struct
madvise_behavior like every one of those operations, which is where the
range, the VMA and the lock-dropped flag it used to be handed separately
already live.

It stays a caller of the interface khugepaged uses, so nothing about the
collapse changes.

The !CONFIG_TRANSPARENT_HUGEPAGE stub moves in with it.

Assisted-by: LLM
Link: https://lore.kernel.org/20260910120238.2529819-13-kirill@shutemov.name
Signed-off-by: Kiryl Shutsemau (Meta) <kas@kernel.org>
Cc: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: Barry Song <baohua@kernel.org>
Cc: David Hildenbrand <david@kernel.org>
Cc: Dev Jain <dev.jain@arm.com>
Cc: Jann Horn <jannh@google.com>
Cc: Lance Yang <lance.yang@linux.dev>
Cc: Liam R. Howlett <liam@infradead.org>
Cc: Lorenzo Stoakes <ljs@kernel.org>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Vlastimil Babka <vbabka@kernel.org>
Cc: Zi Yan <ziy@nvidia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 include/linux/huge_mm.h |    9 --
 mm/khugepaged.c         |  157 -----------------------------------
 mm/madvise.c            |  169 +++++++++++++++++++++++++++++++++++++-
 3 files changed, 169 insertions(+), 166 deletions(-)

--- a/include/linux/huge_mm.h~mm-collapse-implement-madv_collapse-in-madvisec
+++ a/include/linux/huge_mm.h
@@ -510,8 +510,6 @@ change_huge_pud(struct mmu_gather *tlb,
 
 int hugepage_madvise(struct vm_area_struct *vma, vm_flags_t *vm_flags,
 		     int advice);
-int madvise_collapse(struct vm_area_struct *vma, unsigned long start,
-		     unsigned long end, bool *lock_dropped);
 void vma_adjust_trans_huge(struct vm_area_struct *vma, unsigned long start,
 			   unsigned long end, struct vm_area_struct *next);
 spinlock_t *__pmd_trans_huge_lock(pmd_t *pmd, struct vm_area_struct *vma);
@@ -714,13 +712,6 @@ static inline int hugepage_madvise(struc
 {
 	return -EINVAL;
 }
-
-static inline int madvise_collapse(struct vm_area_struct *vma,
-				   unsigned long start,
-				   unsigned long end, bool *lock_dropped)
-{
-	return -EINVAL;
-}
 
 static inline void vma_adjust_trans_huge(struct vm_area_struct *vma,
 					 unsigned long start,
--- a/mm/khugepaged.c~mm-collapse-implement-madv_collapse-in-madvisec
+++ a/mm/khugepaged.c
@@ -969,21 +969,6 @@ static void collapse_policy_khugepaged(s
 	p->tva_type = TVA_KHUGEPAGED;
 }
 
-/* MADV_COLLAPSE was asked for explicitly, so it is not held to those */
-static void collapse_policy_forced(struct collapse_policy *p)
-{
-	p->max_ptes_none = HPAGE_PMD_NR;
-	p->max_ptes_swap = HPAGE_PMD_NR;
-	p->max_ptes_shared = HPAGE_PMD_NR;
-	p->strict_sub_pmd = false;
-	p->skip_lazyfree = false;
-	p->require_referenced = false;
-	p->install_pmd = true;
-	p->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)
 {
@@ -2802,8 +2787,8 @@ enum scan_result collapse_scan_pmd(struc
 	return result;
 }
 
-enum scan_result collapse_run_pmd(struct mm_struct *mm,
-		unsigned long addr, struct collapse_control *cc)
+enum scan_result collapse_run_pmd(struct mm_struct *mm, unsigned long addr,
+		struct collapse_control *cc)
 {
 	struct file *file = cc->scan_file;
 	bool triggered_wb = false;
@@ -3179,141 +3164,3 @@ bool current_is_khugepaged(void)
 {
 	return kthread_func(current) == khugepaged;
 }
-
-static int madvise_collapse_errno(enum scan_result r)
-{
-	/*
-	 * MADV_COLLAPSE breaks from existing madvise(2) conventions to provide
-	 * actionable feedback to caller, so they may take an appropriate
-	 * fallback measure depending on the nature of the failure.
-	 */
-	switch (r) {
-	case SCAN_ALLOC_HUGE_PAGE_FAIL:
-		return -ENOMEM;
-	case SCAN_CGROUP_CHARGE_FAIL:
-	case SCAN_EXCEED_NONE_PTE:
-		return -EBUSY;
-	/* Resource temporary unavailable - trying again might succeed */
-	case SCAN_PAGE_COUNT:
-	case SCAN_PAGE_LOCK:
-	case SCAN_PAGE_LRU:
-	case SCAN_DEL_PAGE_LRU:
-	case SCAN_PAGE_FILLED:
-	case SCAN_PAGE_HAS_PRIVATE:
-	case SCAN_PAGE_DIRTY_OR_WRITEBACK:
-		return -EAGAIN;
-	/*
-	 * Other: Trying again likely not to succeed / error intrinsic to
-	 * specified memory range. khugepaged likely won't be able to collapse
-	 * either.
-	 */
-	default:
-		return -EINVAL;
-	}
-}
-
-int madvise_collapse(struct vm_area_struct *vma, unsigned long start,
-		     unsigned long end, bool *lock_dropped)
-{
-	struct collapse_control *cc;
-	struct mm_struct *mm = vma->vm_mm;
-	unsigned long hstart, hend, addr, orders;
-	enum scan_result last_fail = SCAN_FAIL;
-	int thps = 0;
-
-	BUG_ON(vma->vm_start > start);
-	BUG_ON(vma->vm_end < end);
-
-	orders = collapse_possible_orders(vma, vma->vm_flags,
-					  TVA_FORCED_COLLAPSE);
-	if (!orders)
-		return -EINVAL;
-
-	hstart = ALIGN(start, HPAGE_PMD_SIZE);
-	hend = ALIGN_DOWN(end, HPAGE_PMD_SIZE);
-
-	if (hstart >= hend)
-		return 0;
-
-	cc = kmalloc_obj(*cc);
-	if (!cc)
-		return -ENOMEM;
-	collapse_control_init(cc);
-	collapse_policy_forced(&cc->policy);
-
-	lru_add_drain_all();
-
-	for (addr = hstart; addr < hend; addr += HPAGE_PMD_SIZE) {
-		struct vm_area_struct *found;
-		enum scan_result result;
-
-		/*
-		 * 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);
-			result = collapse_vma_revalidate(mm, addr, false, &found,
-							 cc, HPAGE_PMD_ORDER);
-			if (result != SCAN_SUCCEED) {
-				last_fail = result;
-				goto out_locked;
-			}
-			vma = found;
-			hend = min(hend, vma->vm_end & HPAGE_PMD_MASK);
-			orders = collapse_possible_orders(vma, vma->vm_flags,
-							  cc->policy.tva_type);
-		}
-
-		result = collapse_scan_pmd(vma, addr, cc, orders);
-		/* 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:
-			++thps;
-			break;
-		/* Whitelisted set of results where continuing OK */
-		case SCAN_NO_PTE_TABLE:
-		case SCAN_PTE_NON_PRESENT:
-		case SCAN_PTE_UFFD:
-		case SCAN_LACK_REFERENCED_PAGE:
-		case SCAN_PAGE_NULL:
-		case SCAN_PAGE_COUNT:
-		case SCAN_PAGE_LOCK:
-		case SCAN_PAGE_COMPOUND:
-		case SCAN_PAGE_LRU:
-		case SCAN_DEL_PAGE_LRU:
-			last_fail = result;
-			break;
-		default:
-			last_fail = result;
-			/* Other error, exit */
-			goto out;
-		}
-	}
-
-out:
-	/* Caller expects us to hold mmap_lock on return */
-	if (!vma)
-		mmap_read_lock(mm);
-out_locked:
-	mmap_assert_locked(mm);
-	collapse_control_release(cc);
-	kfree(cc);
-
-	return thps == ((hend - hstart) >> HPAGE_PMD_SHIFT) ? 0
-			: madvise_collapse_errno(last_fail);
-}
--- a/mm/madvise.c~mm-collapse-implement-madv_collapse-in-madvisec
+++ a/mm/madvise.c
@@ -38,6 +38,7 @@
 
 #include "internal.h"
 #include "swap.h"
+#include "collapse.h"
 
 #define __MADV_SET_ANON_VMA_NAME (-1)
 
@@ -906,6 +907,171 @@ bool madvise_dontneed_free_valid_vma(str
 	return true;
 }
 
+#ifdef CONFIG_TRANSPARENT_HUGEPAGE
+
+/* MADV_COLLAPSE was asked for explicitly, so it is not held to those */
+static void collapse_policy_forced(struct collapse_policy *p)
+{
+	p->max_ptes_none = HPAGE_PMD_NR;
+	p->max_ptes_swap = HPAGE_PMD_NR;
+	p->max_ptes_shared = HPAGE_PMD_NR;
+	p->strict_sub_pmd = false;
+	p->skip_lazyfree = false;
+	p->require_referenced = false;
+	p->install_pmd = true;
+	p->writeback_dirty = true;
+	p->gfp = GFP_TRANSHUGE;
+	p->tva_type = TVA_FORCED_COLLAPSE;
+}
+
+static int madvise_collapse_errno(enum scan_result r)
+{
+	/*
+	 * MADV_COLLAPSE breaks from existing madvise(2) conventions to provide
+	 * actionable feedback to caller, so they may take an appropriate
+	 * fallback measure depending on the nature of the failure.
+	 */
+	switch (r) {
+	case SCAN_ALLOC_HUGE_PAGE_FAIL:
+		return -ENOMEM;
+	case SCAN_CGROUP_CHARGE_FAIL:
+	case SCAN_EXCEED_NONE_PTE:
+		return -EBUSY;
+	/* Resource temporary unavailable - trying again might succeed */
+	case SCAN_PAGE_COUNT:
+	case SCAN_PAGE_LOCK:
+	case SCAN_PAGE_LRU:
+	case SCAN_DEL_PAGE_LRU:
+	case SCAN_PAGE_FILLED:
+	case SCAN_PAGE_HAS_PRIVATE:
+	case SCAN_PAGE_DIRTY_OR_WRITEBACK:
+		return -EAGAIN;
+	/*
+	 * Other: Trying again likely not to succeed / error intrinsic to
+	 * specified memory range. khugepaged likely won't be able to collapse
+	 * either.
+	 */
+	default:
+		return -EINVAL;
+	}
+}
+
+static int madvise_collapse(struct madvise_behavior *madv_behavior)
+{
+	struct madvise_behavior_range *range = &madv_behavior->range;
+	struct vm_area_struct *vma = madv_behavior->vma;
+	struct mm_struct *mm = madv_behavior->mm;
+	struct collapse_control *cc;
+	unsigned long hstart, hend, addr, orders;
+	enum scan_result last_fail = SCAN_FAIL;
+	int thps = 0;
+
+	BUG_ON(vma->vm_start > range->start);
+	BUG_ON(vma->vm_end < range->end);
+
+	orders = collapse_possible_orders(vma, vma->vm_flags,
+					  TVA_FORCED_COLLAPSE);
+	if (!orders)
+		return -EINVAL;
+
+	hstart = ALIGN(range->start, HPAGE_PMD_SIZE);
+	hend = ALIGN_DOWN(range->end, HPAGE_PMD_SIZE);
+
+	if (hstart >= hend)
+		return 0;
+
+	cc = kmalloc_obj(*cc);
+	if (!cc)
+		return -ENOMEM;
+	collapse_control_init(cc);
+	collapse_policy_forced(&cc->policy);
+
+	lru_add_drain_all();
+
+	for (addr = hstart; addr < hend; addr += HPAGE_PMD_SIZE) {
+		struct vm_area_struct *found;
+		enum scan_result result;
+
+		/*
+		 * 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);
+			result = collapse_vma_revalidate(mm, addr, false, &found,
+							 cc, HPAGE_PMD_ORDER);
+			if (result != SCAN_SUCCEED) {
+				last_fail = result;
+				goto out_locked;
+			}
+			vma = found;
+			hend = min(hend, vma->vm_end & HPAGE_PMD_MASK);
+			orders = collapse_possible_orders(vma, vma->vm_flags,
+							  cc->policy.tva_type);
+		}
+
+		result = collapse_scan_pmd(vma, addr, cc, orders);
+		/* 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);
+		mark_mmap_lock_dropped(madv_behavior);
+		vma = NULL;
+
+		result = collapse_run_pmd(mm, addr, cc);
+tally:
+		switch (result) {
+		case SCAN_SUCCEED:
+		case SCAN_PMD_MAPPED:
+			++thps;
+			break;
+		/* Whitelisted set of results where continuing OK */
+		case SCAN_NO_PTE_TABLE:
+		case SCAN_PTE_NON_PRESENT:
+		case SCAN_PTE_UFFD:
+		case SCAN_LACK_REFERENCED_PAGE:
+		case SCAN_PAGE_NULL:
+		case SCAN_PAGE_COUNT:
+		case SCAN_PAGE_LOCK:
+		case SCAN_PAGE_COMPOUND:
+		case SCAN_PAGE_LRU:
+		case SCAN_DEL_PAGE_LRU:
+			last_fail = result;
+			break;
+		default:
+			last_fail = result;
+			/* Other error, exit */
+			goto out;
+		}
+	}
+
+out:
+	/* Caller expects us to hold mmap_lock on return */
+	if (!vma)
+		mmap_read_lock(mm);
+out_locked:
+	mmap_assert_locked(mm);
+	collapse_control_release(cc);
+	kfree(cc);
+
+	return thps == ((hend - hstart) >> HPAGE_PMD_SHIFT) ? 0
+			: madvise_collapse_errno(last_fail);
+}
+
+#else	/* CONFIG_TRANSPARENT_HUGEPAGE */
+
+static int madvise_collapse(struct madvise_behavior *madv_behavior)
+{
+	return -EINVAL;
+}
+
+#endif	/* CONFIG_TRANSPARENT_HUGEPAGE */
+
 static long madvise_dontneed_free(struct madvise_behavior *madv_behavior)
 {
 	struct mm_struct *mm = madv_behavior->mm;
@@ -1373,8 +1539,7 @@ static int madvise_vma_behavior(struct m
 	case MADV_DONTNEED_LOCKED:
 		return madvise_dontneed_free(madv_behavior);
 	case MADV_COLLAPSE:
-		return madvise_collapse(vma, range->start, range->end,
-			&madv_behavior->lock_dropped);
+		return madvise_collapse(madv_behavior);
 	case MADV_GUARD_INSTALL:
 		return madvise_guard_install(madv_behavior);
 	case MADV_GUARD_REMOVE:
_

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