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Message-Id: <20260118123442.f55db3e141388836df0c7785@linux-foundation.org>
Date: Sun, 18 Jan 2026 12:34:42 -0800
From: Andrew Morton <akpm@...ux-foundation.org>
To: Shivank Garg <shivankg@....com>
Cc: David Hildenbrand <david@...nel.org>, Lorenzo Stoakes
<lorenzo.stoakes@...cle.com>, Zi Yan <ziy@...dia.com>, Baolin Wang
<baolin.wang@...ux.alibaba.com>, "Liam R . Howlett"
<Liam.Howlett@...cle.com>, Nico Pache <npache@...hat.com>, Ryan Roberts
<ryan.roberts@....com>, Dev Jain <dev.jain@....com>, Barry Song
<baohua@...nel.org>, Lance Yang <lance.yang@...ux.dev>,
<linux-mm@...ck.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH V3 0/5] mm/khugepaged: cleanups and scan limit fix
On Sun, 18 Jan 2026 19:22:51 +0000 Shivank Garg <shivankg@....com> wrote:
> This series contains several cleanups for mm/khugepaged.c to improve code
> readability and type safety, and one functional fix to ensure
> khugepaged_scan_mm_slot() correctly accounts for small VMAs towards
> scan limit.
>
That's a lot of changes to a well-reviewed 24 day old patchset.
>
> v3:
> - Fold mm-khugepaged-count-small-vmas-towards-scan-limit-fix: add comment (Lance)
> - Remove extern and use two tabs indent (David)
Are you sure? The v2->v3 diff is large. A lot of (unchangelogged)
alterations from `int' to `enum scan_result'.
It all looks pretty simple/straightforward to me but again, can
reviewers please check this over fairly soonly, thanks.
--- a/include/linux/khugepaged.h~b
+++ a/include/linux/khugepaged.h
@@ -17,8 +17,8 @@ extern void khugepaged_enter_vma(struct
vm_flags_t vm_flags);
extern void khugepaged_min_free_kbytes_update(void);
extern bool current_is_khugepaged(void);
-extern void collapse_pte_mapped_thp(struct mm_struct *mm, unsigned long addr,
- bool install_pmd);
+void collapse_pte_mapped_thp(struct mm_struct *mm, unsigned long addr,
+ bool install_pmd);
static inline void khugepaged_fork(struct mm_struct *mm, struct mm_struct *oldmm)
{
@@ -43,7 +43,7 @@ static inline void khugepaged_enter_vma(
{
}
static inline void collapse_pte_mapped_thp(struct mm_struct *mm,
- unsigned long addr, bool install_pmd)
+ unsigned long addr, bool install_pmd)
{
}
--- a/mm/khugepaged.c~b
+++ a/mm/khugepaged.c
@@ -537,17 +537,16 @@ static void release_pte_pages(pte_t *pte
}
}
-static int __collapse_huge_page_isolate(struct vm_area_struct *vma,
- unsigned long start_addr,
- pte_t *pte,
- struct collapse_control *cc,
- struct list_head *compound_pagelist)
+static enum scan_result __collapse_huge_page_isolate(struct vm_area_struct *vma,
+ unsigned long start_addr, pte_t *pte, struct collapse_control *cc,
+ struct list_head *compound_pagelist)
{
struct page *page = NULL;
struct folio *folio = NULL;
unsigned long addr = start_addr;
pte_t *_pte;
- int none_or_zero = 0, shared = 0, result = SCAN_FAIL, referenced = 0;
+ int none_or_zero = 0, shared = 0, referenced = 0;
+ enum scan_result result = SCAN_FAIL;
for (_pte = pte; _pte < pte + HPAGE_PMD_NR;
_pte++, addr += PAGE_SIZE) {
@@ -780,13 +779,13 @@ static void __collapse_huge_page_copy_fa
* @ptl: lock on raw pages' PTEs
* @compound_pagelist: list that stores compound pages
*/
-static int __collapse_huge_page_copy(pte_t *pte, struct folio *folio,
+static enum scan_result __collapse_huge_page_copy(pte_t *pte, struct folio *folio,
pmd_t *pmd, pmd_t orig_pmd, struct vm_area_struct *vma,
unsigned long address, spinlock_t *ptl,
struct list_head *compound_pagelist)
{
unsigned int i;
- int result = SCAN_SUCCEED;
+ enum scan_result result = SCAN_SUCCEED;
/*
* Copying pages' contents is subject to memory poison at any iteration.
@@ -898,10 +897,8 @@ static int hpage_collapse_find_target_no
* Returns enum scan_result value.
*/
-static int hugepage_vma_revalidate(struct mm_struct *mm, unsigned long address,
- bool expect_anon,
- struct vm_area_struct **vmap,
- struct collapse_control *cc)
+static enum scan_result hugepage_vma_revalidate(struct mm_struct *mm, unsigned long address,
+ bool expect_anon, struct vm_area_struct **vmap, struct collapse_control *cc)
{
struct vm_area_struct *vma;
enum tva_type type = cc->is_khugepaged ? TVA_KHUGEPAGED :
@@ -930,7 +927,7 @@ static int hugepage_vma_revalidate(struc
return SCAN_SUCCEED;
}
-static inline int check_pmd_state(pmd_t *pmd)
+static inline enum scan_result check_pmd_state(pmd_t *pmd)
{
pmd_t pmde = pmdp_get_lockless(pmd);
@@ -953,9 +950,8 @@ static inline int check_pmd_state(pmd_t
return SCAN_SUCCEED;
}
-static int find_pmd_or_thp_or_none(struct mm_struct *mm,
- unsigned long address,
- pmd_t **pmd)
+static enum scan_result find_pmd_or_thp_or_none(struct mm_struct *mm,
+ unsigned long address, pmd_t **pmd)
{
*pmd = mm_find_pmd(mm, address);
if (!*pmd)
@@ -964,12 +960,11 @@ static int find_pmd_or_thp_or_none(struc
return check_pmd_state(*pmd);
}
-static int check_pmd_still_valid(struct mm_struct *mm,
- unsigned long address,
- pmd_t *pmd)
+static enum scan_result check_pmd_still_valid(struct mm_struct *mm,
+ unsigned long address, pmd_t *pmd)
{
pmd_t *new_pmd;
- int result = find_pmd_or_thp_or_none(mm, address, &new_pmd);
+ enum scan_result result = find_pmd_or_thp_or_none(mm, address, &new_pmd);
if (result != SCAN_SUCCEED)
return result;
@@ -985,15 +980,14 @@ static int check_pmd_still_valid(struct
* Called and returns without pte mapped or spinlocks held.
* Returns result: if not SCAN_SUCCEED, mmap_lock has been released.
*/
-static int __collapse_huge_page_swapin(struct mm_struct *mm,
- struct vm_area_struct *vma,
- unsigned long start_addr, pmd_t *pmd,
- int referenced)
+static enum scan_result __collapse_huge_page_swapin(struct mm_struct *mm,
+ struct vm_area_struct *vma, unsigned long start_addr, pmd_t *pmd,
+ int referenced)
{
int swapped_in = 0;
vm_fault_t ret = 0;
unsigned long addr, end = start_addr + (HPAGE_PMD_NR * PAGE_SIZE);
- int result;
+ enum scan_result result;
pte_t *pte = NULL;
spinlock_t *ptl;
@@ -1062,8 +1056,8 @@ out:
return result;
}
-static int alloc_charge_folio(struct folio **foliop, struct mm_struct *mm,
- struct collapse_control *cc)
+static enum scan_result alloc_charge_folio(struct folio **foliop, struct mm_struct *mm,
+ struct collapse_control *cc)
{
gfp_t gfp = (cc->is_khugepaged ? alloc_hugepage_khugepaged_gfpmask() :
GFP_TRANSHUGE);
@@ -1090,9 +1084,8 @@ static int alloc_charge_folio(struct fol
return SCAN_SUCCEED;
}
-static int collapse_huge_page(struct mm_struct *mm, unsigned long address,
- int referenced, int unmapped,
- struct collapse_control *cc)
+static enum scan_result collapse_huge_page(struct mm_struct *mm, unsigned long address,
+ int referenced, int unmapped, struct collapse_control *cc)
{
LIST_HEAD(compound_pagelist);
pmd_t *pmd, _pmd;
@@ -1100,7 +1093,7 @@ static int collapse_huge_page(struct mm_
pgtable_t pgtable;
struct folio *folio;
spinlock_t *pmd_ptl, *pte_ptl;
- int result = SCAN_FAIL;
+ enum scan_result result = SCAN_FAIL;
struct vm_area_struct *vma;
struct mmu_notifier_range range;
@@ -1246,15 +1239,14 @@ out_nolock:
return result;
}
-static int hpage_collapse_scan_pmd(struct mm_struct *mm,
- struct vm_area_struct *vma,
- unsigned long start_addr, bool *mmap_locked,
- struct collapse_control *cc)
+static enum scan_result hpage_collapse_scan_pmd(struct mm_struct *mm,
+ struct vm_area_struct *vma, unsigned long start_addr, bool *mmap_locked,
+ struct collapse_control *cc)
{
pmd_t *pmd;
pte_t *pte, *_pte;
- int result = SCAN_FAIL, referenced = 0;
- int none_or_zero = 0, shared = 0;
+ int none_or_zero = 0, shared = 0, referenced = 0;
+ enum scan_result result = SCAN_FAIL;
struct page *page = NULL;
struct folio *folio = NULL;
unsigned long addr;
@@ -1441,8 +1433,8 @@ static void collect_mm_slot(struct mm_sl
}
/* folio must be locked, and mmap_lock must be held */
-static int set_huge_pmd(struct vm_area_struct *vma, unsigned long addr,
- pmd_t *pmdp, struct folio *folio, struct page *page)
+static enum scan_result set_huge_pmd(struct vm_area_struct *vma, unsigned long addr,
+ pmd_t *pmdp, struct folio *folio, struct page *page)
{
struct mm_struct *mm = vma->vm_mm;
struct vm_fault vmf = {
@@ -1477,10 +1469,11 @@ static int set_huge_pmd(struct vm_area_s
return SCAN_SUCCEED;
}
-static int try_collapse_pte_mapped_thp(struct mm_struct *mm, unsigned long addr,
- bool install_pmd)
+static enum scan_result try_collapse_pte_mapped_thp(struct mm_struct *mm, unsigned long addr,
+ bool install_pmd)
{
- int nr_mapped_ptes = 0, result = SCAN_FAIL;
+ enum scan_result result = SCAN_FAIL;
+ int nr_mapped_ptes = 0;
unsigned int nr_batch_ptes;
struct mmu_notifier_range range;
bool notified = false;
@@ -1712,7 +1705,7 @@ drop_folio:
* as pmd-mapped. Possibly install a huge PMD mapping the THP.
*/
void collapse_pte_mapped_thp(struct mm_struct *mm, unsigned long addr,
- bool install_pmd)
+ bool install_pmd)
{
try_collapse_pte_mapped_thp(mm, addr, install_pmd);
}
@@ -1862,9 +1855,8 @@ drop_pml:
* + unlock old pages
* + unlock and free huge page;
*/
-static int collapse_file(struct mm_struct *mm, unsigned long addr,
- struct file *file, pgoff_t start,
- struct collapse_control *cc)
+static enum scan_result collapse_file(struct mm_struct *mm, unsigned long addr,
+ struct file *file, pgoff_t start, struct collapse_control *cc)
{
struct address_space *mapping = file->f_mapping;
struct page *dst;
@@ -1872,7 +1864,8 @@ static int collapse_file(struct mm_struc
pgoff_t index = 0, end = start + HPAGE_PMD_NR;
LIST_HEAD(pagelist);
XA_STATE_ORDER(xas, &mapping->i_pages, start, HPAGE_PMD_ORDER);
- int nr_none = 0, result = SCAN_SUCCEED;
+ enum scan_result result = SCAN_SUCCEED;
+ int nr_none = 0;
bool is_shmem = shmem_file(file);
VM_BUG_ON(!IS_ENABLED(CONFIG_READ_ONLY_THP_FOR_FS) && !is_shmem);
@@ -2293,16 +2286,15 @@ out:
return result;
}
-static int hpage_collapse_scan_file(struct mm_struct *mm, unsigned long addr,
- struct file *file, pgoff_t start,
- struct collapse_control *cc)
+static enum scan_result hpage_collapse_scan_file(struct mm_struct *mm, unsigned long addr,
+ struct file *file, pgoff_t start, struct collapse_control *cc)
{
struct folio *folio = NULL;
struct address_space *mapping = file->f_mapping;
XA_STATE(xas, &mapping->i_pages, start);
int present, swap;
int node = NUMA_NO_NODE;
- int result = SCAN_SUCCEED;
+ enum scan_result result = SCAN_SUCCEED;
present = 0;
swap = 0;
@@ -2400,7 +2392,7 @@ static int hpage_collapse_scan_file(stru
return result;
}
-static unsigned int khugepaged_scan_mm_slot(unsigned int pages, int *result,
+static unsigned int khugepaged_scan_mm_slot(unsigned int pages, enum scan_result *result,
struct collapse_control *cc)
__releases(&khugepaged_mm_lock)
__acquires(&khugepaged_mm_lock)
@@ -2562,7 +2554,7 @@ static void khugepaged_do_scan(struct co
unsigned int progress = 0, pass_through_head = 0;
unsigned int pages = READ_ONCE(khugepaged_pages_to_scan);
bool wait = true;
- int result = SCAN_SUCCEED;
+ enum scan_result result = SCAN_SUCCEED;
lru_add_drain_all();
@@ -2775,7 +2767,8 @@ int madvise_collapse(struct vm_area_stru
struct collapse_control *cc;
struct mm_struct *mm = vma->vm_mm;
unsigned long hstart, hend, addr;
- int thps = 0, last_fail = SCAN_FAIL;
+ enum scan_result last_fail = SCAN_FAIL;
+ int thps = 0;
bool mmap_locked = true;
BUG_ON(vma->vm_start > start);
@@ -2796,7 +2789,7 @@ int madvise_collapse(struct vm_area_stru
hend = end & HPAGE_PMD_MASK;
for (addr = hstart; addr < hend; addr += HPAGE_PMD_SIZE) {
- int result = SCAN_FAIL;
+ enum scan_result result = SCAN_FAIL;
bool triggered_wb = false;
retry:
_
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