linux-stable/mm/khugepaged.c
Yang Shi a4aeaa06d4 mm: khugepaged: skip huge page collapse for special files
The read-only THP for filesystems will collapse THP for files opened
readonly and mapped with VM_EXEC.  The intended usecase is to avoid TLB
misses for large text segments.  But it doesn't restrict the file types
so a THP could be collapsed for a non-regular file, for example, block
device, if it is opened readonly and mapped with EXEC permission.  This
may cause bugs, like [1] and [2].

This is definitely not the intended usecase, so just collapse THP for
regular files in order to close the attack surface.

[shy828301@gmail.com: fix vm_file check [3]]

Link: https://lore.kernel.org/lkml/CACkBjsYwLYLRmX8GpsDpMthagWOjWWrNxqY6ZLNQVr6yx+f5vA@mail.gmail.com/ [1]
Link: https://lore.kernel.org/linux-mm/000000000000c6a82505ce284e4c@google.com/ [2]
Link: https://lkml.kernel.org/r/CAHbLzkqTW9U3VvTu1Ki5v_cLRC9gHW+znBukg_ycergE0JWj-A@mail.gmail.com [3]
Link: https://lkml.kernel.org/r/20211027195221.3825-1-shy828301@gmail.com
Fixes: 99cb0dbd47 ("mm,thp: add read-only THP support for (non-shmem) FS")
Signed-off-by: Hugh Dickins <hughd@google.com>
Signed-off-by: Yang Shi <shy828301@gmail.com>
Reported-by: Hao Sun <sunhao.th@gmail.com>
Reported-by: syzbot+aae069be1de40fb11825@syzkaller.appspotmail.com
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Song Liu <songliubraving@fb.com>
Cc: Andrea Righi <andrea.righi@canonical.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2021-10-28 17:18:55 -07:00

2375 lines
59 KiB
C

// SPDX-License-Identifier: GPL-2.0
#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
#include <linux/mm.h>
#include <linux/sched.h>
#include <linux/sched/mm.h>
#include <linux/sched/coredump.h>
#include <linux/mmu_notifier.h>
#include <linux/rmap.h>
#include <linux/swap.h>
#include <linux/mm_inline.h>
#include <linux/kthread.h>
#include <linux/khugepaged.h>
#include <linux/freezer.h>
#include <linux/mman.h>
#include <linux/hashtable.h>
#include <linux/userfaultfd_k.h>
#include <linux/page_idle.h>
#include <linux/swapops.h>
#include <linux/shmem_fs.h>
#include <asm/tlb.h>
#include <asm/pgalloc.h>
#include "internal.h"
enum scan_result {
SCAN_FAIL,
SCAN_SUCCEED,
SCAN_PMD_NULL,
SCAN_EXCEED_NONE_PTE,
SCAN_EXCEED_SWAP_PTE,
SCAN_EXCEED_SHARED_PTE,
SCAN_PTE_NON_PRESENT,
SCAN_PTE_UFFD_WP,
SCAN_PAGE_RO,
SCAN_LACK_REFERENCED_PAGE,
SCAN_PAGE_NULL,
SCAN_SCAN_ABORT,
SCAN_PAGE_COUNT,
SCAN_PAGE_LRU,
SCAN_PAGE_LOCK,
SCAN_PAGE_ANON,
SCAN_PAGE_COMPOUND,
SCAN_ANY_PROCESS,
SCAN_VMA_NULL,
SCAN_VMA_CHECK,
SCAN_ADDRESS_RANGE,
SCAN_SWAP_CACHE_PAGE,
SCAN_DEL_PAGE_LRU,
SCAN_ALLOC_HUGE_PAGE_FAIL,
SCAN_CGROUP_CHARGE_FAIL,
SCAN_TRUNCATED,
SCAN_PAGE_HAS_PRIVATE,
};
#define CREATE_TRACE_POINTS
#include <trace/events/huge_memory.h>
static struct task_struct *khugepaged_thread __read_mostly;
static DEFINE_MUTEX(khugepaged_mutex);
/* default scan 8*512 pte (or vmas) every 30 second */
static unsigned int khugepaged_pages_to_scan __read_mostly;
static unsigned int khugepaged_pages_collapsed;
static unsigned int khugepaged_full_scans;
static unsigned int khugepaged_scan_sleep_millisecs __read_mostly = 10000;
/* during fragmentation poll the hugepage allocator once every minute */
static unsigned int khugepaged_alloc_sleep_millisecs __read_mostly = 60000;
static unsigned long khugepaged_sleep_expire;
static DEFINE_SPINLOCK(khugepaged_mm_lock);
static DECLARE_WAIT_QUEUE_HEAD(khugepaged_wait);
/*
* default collapse hugepages if there is at least one pte mapped like
* it would have happened if the vma was large enough during page
* fault.
*/
static unsigned int khugepaged_max_ptes_none __read_mostly;
static unsigned int khugepaged_max_ptes_swap __read_mostly;
static unsigned int khugepaged_max_ptes_shared __read_mostly;
#define MM_SLOTS_HASH_BITS 10
static __read_mostly DEFINE_HASHTABLE(mm_slots_hash, MM_SLOTS_HASH_BITS);
static struct kmem_cache *mm_slot_cache __read_mostly;
#define MAX_PTE_MAPPED_THP 8
/**
* struct mm_slot - hash lookup from mm to mm_slot
* @hash: hash collision list
* @mm_node: khugepaged scan list headed in khugepaged_scan.mm_head
* @mm: the mm that this information is valid for
* @nr_pte_mapped_thp: number of pte mapped THP
* @pte_mapped_thp: address array corresponding pte mapped THP
*/
struct mm_slot {
struct hlist_node hash;
struct list_head mm_node;
struct mm_struct *mm;
/* pte-mapped THP in this mm */
int nr_pte_mapped_thp;
unsigned long pte_mapped_thp[MAX_PTE_MAPPED_THP];
};
/**
* struct khugepaged_scan - cursor for scanning
* @mm_head: the head of the mm list to scan
* @mm_slot: the current mm_slot we are scanning
* @address: the next address inside that to be scanned
*
* There is only the one khugepaged_scan instance of this cursor structure.
*/
struct khugepaged_scan {
struct list_head mm_head;
struct mm_slot *mm_slot;
unsigned long address;
};
static struct khugepaged_scan khugepaged_scan = {
.mm_head = LIST_HEAD_INIT(khugepaged_scan.mm_head),
};
#ifdef CONFIG_SYSFS
static ssize_t scan_sleep_millisecs_show(struct kobject *kobj,
struct kobj_attribute *attr,
char *buf)
{
return sysfs_emit(buf, "%u\n", khugepaged_scan_sleep_millisecs);
}
static ssize_t scan_sleep_millisecs_store(struct kobject *kobj,
struct kobj_attribute *attr,
const char *buf, size_t count)
{
unsigned int msecs;
int err;
err = kstrtouint(buf, 10, &msecs);
if (err)
return -EINVAL;
khugepaged_scan_sleep_millisecs = msecs;
khugepaged_sleep_expire = 0;
wake_up_interruptible(&khugepaged_wait);
return count;
}
static struct kobj_attribute scan_sleep_millisecs_attr =
__ATTR(scan_sleep_millisecs, 0644, scan_sleep_millisecs_show,
scan_sleep_millisecs_store);
static ssize_t alloc_sleep_millisecs_show(struct kobject *kobj,
struct kobj_attribute *attr,
char *buf)
{
return sysfs_emit(buf, "%u\n", khugepaged_alloc_sleep_millisecs);
}
static ssize_t alloc_sleep_millisecs_store(struct kobject *kobj,
struct kobj_attribute *attr,
const char *buf, size_t count)
{
unsigned int msecs;
int err;
err = kstrtouint(buf, 10, &msecs);
if (err)
return -EINVAL;
khugepaged_alloc_sleep_millisecs = msecs;
khugepaged_sleep_expire = 0;
wake_up_interruptible(&khugepaged_wait);
return count;
}
static struct kobj_attribute alloc_sleep_millisecs_attr =
__ATTR(alloc_sleep_millisecs, 0644, alloc_sleep_millisecs_show,
alloc_sleep_millisecs_store);
static ssize_t pages_to_scan_show(struct kobject *kobj,
struct kobj_attribute *attr,
char *buf)
{
return sysfs_emit(buf, "%u\n", khugepaged_pages_to_scan);
}
static ssize_t pages_to_scan_store(struct kobject *kobj,
struct kobj_attribute *attr,
const char *buf, size_t count)
{
unsigned int pages;
int err;
err = kstrtouint(buf, 10, &pages);
if (err || !pages)
return -EINVAL;
khugepaged_pages_to_scan = pages;
return count;
}
static struct kobj_attribute pages_to_scan_attr =
__ATTR(pages_to_scan, 0644, pages_to_scan_show,
pages_to_scan_store);
static ssize_t pages_collapsed_show(struct kobject *kobj,
struct kobj_attribute *attr,
char *buf)
{
return sysfs_emit(buf, "%u\n", khugepaged_pages_collapsed);
}
static struct kobj_attribute pages_collapsed_attr =
__ATTR_RO(pages_collapsed);
static ssize_t full_scans_show(struct kobject *kobj,
struct kobj_attribute *attr,
char *buf)
{
return sysfs_emit(buf, "%u\n", khugepaged_full_scans);
}
static struct kobj_attribute full_scans_attr =
__ATTR_RO(full_scans);
static ssize_t khugepaged_defrag_show(struct kobject *kobj,
struct kobj_attribute *attr, char *buf)
{
return single_hugepage_flag_show(kobj, attr, buf,
TRANSPARENT_HUGEPAGE_DEFRAG_KHUGEPAGED_FLAG);
}
static ssize_t khugepaged_defrag_store(struct kobject *kobj,
struct kobj_attribute *attr,
const char *buf, size_t count)
{
return single_hugepage_flag_store(kobj, attr, buf, count,
TRANSPARENT_HUGEPAGE_DEFRAG_KHUGEPAGED_FLAG);
}
static struct kobj_attribute khugepaged_defrag_attr =
__ATTR(defrag, 0644, khugepaged_defrag_show,
khugepaged_defrag_store);
/*
* max_ptes_none controls if khugepaged should collapse hugepages over
* any unmapped ptes in turn potentially increasing the memory
* footprint of the vmas. When max_ptes_none is 0 khugepaged will not
* reduce the available free memory in the system as it
* runs. Increasing max_ptes_none will instead potentially reduce the
* free memory in the system during the khugepaged scan.
*/
static ssize_t khugepaged_max_ptes_none_show(struct kobject *kobj,
struct kobj_attribute *attr,
char *buf)
{
return sysfs_emit(buf, "%u\n", khugepaged_max_ptes_none);
}
static ssize_t khugepaged_max_ptes_none_store(struct kobject *kobj,
struct kobj_attribute *attr,
const char *buf, size_t count)
{
int err;
unsigned long max_ptes_none;
err = kstrtoul(buf, 10, &max_ptes_none);
if (err || max_ptes_none > HPAGE_PMD_NR-1)
return -EINVAL;
khugepaged_max_ptes_none = max_ptes_none;
return count;
}
static struct kobj_attribute khugepaged_max_ptes_none_attr =
__ATTR(max_ptes_none, 0644, khugepaged_max_ptes_none_show,
khugepaged_max_ptes_none_store);
static ssize_t khugepaged_max_ptes_swap_show(struct kobject *kobj,
struct kobj_attribute *attr,
char *buf)
{
return sysfs_emit(buf, "%u\n", khugepaged_max_ptes_swap);
}
static ssize_t khugepaged_max_ptes_swap_store(struct kobject *kobj,
struct kobj_attribute *attr,
const char *buf, size_t count)
{
int err;
unsigned long max_ptes_swap;
err = kstrtoul(buf, 10, &max_ptes_swap);
if (err || max_ptes_swap > HPAGE_PMD_NR-1)
return -EINVAL;
khugepaged_max_ptes_swap = max_ptes_swap;
return count;
}
static struct kobj_attribute khugepaged_max_ptes_swap_attr =
__ATTR(max_ptes_swap, 0644, khugepaged_max_ptes_swap_show,
khugepaged_max_ptes_swap_store);
static ssize_t khugepaged_max_ptes_shared_show(struct kobject *kobj,
struct kobj_attribute *attr,
char *buf)
{
return sysfs_emit(buf, "%u\n", khugepaged_max_ptes_shared);
}
static ssize_t khugepaged_max_ptes_shared_store(struct kobject *kobj,
struct kobj_attribute *attr,
const char *buf, size_t count)
{
int err;
unsigned long max_ptes_shared;
err = kstrtoul(buf, 10, &max_ptes_shared);
if (err || max_ptes_shared > HPAGE_PMD_NR-1)
return -EINVAL;
khugepaged_max_ptes_shared = max_ptes_shared;
return count;
}
static struct kobj_attribute khugepaged_max_ptes_shared_attr =
__ATTR(max_ptes_shared, 0644, khugepaged_max_ptes_shared_show,
khugepaged_max_ptes_shared_store);
static struct attribute *khugepaged_attr[] = {
&khugepaged_defrag_attr.attr,
&khugepaged_max_ptes_none_attr.attr,
&khugepaged_max_ptes_swap_attr.attr,
&khugepaged_max_ptes_shared_attr.attr,
&pages_to_scan_attr.attr,
&pages_collapsed_attr.attr,
&full_scans_attr.attr,
&scan_sleep_millisecs_attr.attr,
&alloc_sleep_millisecs_attr.attr,
NULL,
};
struct attribute_group khugepaged_attr_group = {
.attrs = khugepaged_attr,
.name = "khugepaged",
};
#endif /* CONFIG_SYSFS */
int hugepage_madvise(struct vm_area_struct *vma,
unsigned long *vm_flags, int advice)
{
switch (advice) {
case MADV_HUGEPAGE:
#ifdef CONFIG_S390
/*
* qemu blindly sets MADV_HUGEPAGE on all allocations, but s390
* can't handle this properly after s390_enable_sie, so we simply
* ignore the madvise to prevent qemu from causing a SIGSEGV.
*/
if (mm_has_pgste(vma->vm_mm))
return 0;
#endif
*vm_flags &= ~VM_NOHUGEPAGE;
*vm_flags |= VM_HUGEPAGE;
/*
* If the vma become good for khugepaged to scan,
* register it here without waiting a page fault that
* may not happen any time soon.
*/
if (!(*vm_flags & VM_NO_KHUGEPAGED) &&
khugepaged_enter_vma_merge(vma, *vm_flags))
return -ENOMEM;
break;
case MADV_NOHUGEPAGE:
*vm_flags &= ~VM_HUGEPAGE;
*vm_flags |= VM_NOHUGEPAGE;
/*
* Setting VM_NOHUGEPAGE will prevent khugepaged from scanning
* this vma even if we leave the mm registered in khugepaged if
* it got registered before VM_NOHUGEPAGE was set.
*/
break;
}
return 0;
}
int __init khugepaged_init(void)
{
mm_slot_cache = kmem_cache_create("khugepaged_mm_slot",
sizeof(struct mm_slot),
__alignof__(struct mm_slot), 0, NULL);
if (!mm_slot_cache)
return -ENOMEM;
khugepaged_pages_to_scan = HPAGE_PMD_NR * 8;
khugepaged_max_ptes_none = HPAGE_PMD_NR - 1;
khugepaged_max_ptes_swap = HPAGE_PMD_NR / 8;
khugepaged_max_ptes_shared = HPAGE_PMD_NR / 2;
return 0;
}
void __init khugepaged_destroy(void)
{
kmem_cache_destroy(mm_slot_cache);
}
static inline struct mm_slot *alloc_mm_slot(void)
{
if (!mm_slot_cache) /* initialization failed */
return NULL;
return kmem_cache_zalloc(mm_slot_cache, GFP_KERNEL);
}
static inline void free_mm_slot(struct mm_slot *mm_slot)
{
kmem_cache_free(mm_slot_cache, mm_slot);
}
static struct mm_slot *get_mm_slot(struct mm_struct *mm)
{
struct mm_slot *mm_slot;
hash_for_each_possible(mm_slots_hash, mm_slot, hash, (unsigned long)mm)
if (mm == mm_slot->mm)
return mm_slot;
return NULL;
}
static void insert_to_mm_slots_hash(struct mm_struct *mm,
struct mm_slot *mm_slot)
{
mm_slot->mm = mm;
hash_add(mm_slots_hash, &mm_slot->hash, (long)mm);
}
static inline int khugepaged_test_exit(struct mm_struct *mm)
{
return atomic_read(&mm->mm_users) == 0;
}
static bool hugepage_vma_check(struct vm_area_struct *vma,
unsigned long vm_flags)
{
if (!transhuge_vma_enabled(vma, vm_flags))
return false;
if (vma->vm_file && !IS_ALIGNED((vma->vm_start >> PAGE_SHIFT) -
vma->vm_pgoff, HPAGE_PMD_NR))
return false;
/* Enabled via shmem mount options or sysfs settings. */
if (shmem_file(vma->vm_file))
return shmem_huge_enabled(vma);
/* THP settings require madvise. */
if (!(vm_flags & VM_HUGEPAGE) && !khugepaged_always())
return false;
/* Only regular file is valid */
if (IS_ENABLED(CONFIG_READ_ONLY_THP_FOR_FS) && vma->vm_file &&
(vm_flags & VM_EXEC)) {
struct inode *inode = vma->vm_file->f_inode;
return !inode_is_open_for_write(inode) &&
S_ISREG(inode->i_mode);
}
if (!vma->anon_vma || vma->vm_ops)
return false;
if (vma_is_temporary_stack(vma))
return false;
return !(vm_flags & VM_NO_KHUGEPAGED);
}
int __khugepaged_enter(struct mm_struct *mm)
{
struct mm_slot *mm_slot;
int wakeup;
mm_slot = alloc_mm_slot();
if (!mm_slot)
return -ENOMEM;
/* __khugepaged_exit() must not run from under us */
VM_BUG_ON_MM(khugepaged_test_exit(mm), mm);
if (unlikely(test_and_set_bit(MMF_VM_HUGEPAGE, &mm->flags))) {
free_mm_slot(mm_slot);
return 0;
}
spin_lock(&khugepaged_mm_lock);
insert_to_mm_slots_hash(mm, mm_slot);
/*
* Insert just behind the scanning cursor, to let the area settle
* down a little.
*/
wakeup = list_empty(&khugepaged_scan.mm_head);
list_add_tail(&mm_slot->mm_node, &khugepaged_scan.mm_head);
spin_unlock(&khugepaged_mm_lock);
mmgrab(mm);
if (wakeup)
wake_up_interruptible(&khugepaged_wait);
return 0;
}
int khugepaged_enter_vma_merge(struct vm_area_struct *vma,
unsigned long vm_flags)
{
unsigned long hstart, hend;
/*
* khugepaged only supports read-only files for non-shmem files.
* khugepaged does not yet work on special mappings. And
* file-private shmem THP is not supported.
*/
if (!hugepage_vma_check(vma, vm_flags))
return 0;
hstart = (vma->vm_start + ~HPAGE_PMD_MASK) & HPAGE_PMD_MASK;
hend = vma->vm_end & HPAGE_PMD_MASK;
if (hstart < hend)
return khugepaged_enter(vma, vm_flags);
return 0;
}
void __khugepaged_exit(struct mm_struct *mm)
{
struct mm_slot *mm_slot;
int free = 0;
spin_lock(&khugepaged_mm_lock);
mm_slot = get_mm_slot(mm);
if (mm_slot && khugepaged_scan.mm_slot != mm_slot) {
hash_del(&mm_slot->hash);
list_del(&mm_slot->mm_node);
free = 1;
}
spin_unlock(&khugepaged_mm_lock);
if (free) {
clear_bit(MMF_VM_HUGEPAGE, &mm->flags);
free_mm_slot(mm_slot);
mmdrop(mm);
} else if (mm_slot) {
/*
* This is required to serialize against
* khugepaged_test_exit() (which is guaranteed to run
* under mmap sem read mode). Stop here (after we
* return all pagetables will be destroyed) until
* khugepaged has finished working on the pagetables
* under the mmap_lock.
*/
mmap_write_lock(mm);
mmap_write_unlock(mm);
}
}
static void release_pte_page(struct page *page)
{
mod_node_page_state(page_pgdat(page),
NR_ISOLATED_ANON + page_is_file_lru(page),
-compound_nr(page));
unlock_page(page);
putback_lru_page(page);
}
static void release_pte_pages(pte_t *pte, pte_t *_pte,
struct list_head *compound_pagelist)
{
struct page *page, *tmp;
while (--_pte >= pte) {
pte_t pteval = *_pte;
page = pte_page(pteval);
if (!pte_none(pteval) && !is_zero_pfn(pte_pfn(pteval)) &&
!PageCompound(page))
release_pte_page(page);
}
list_for_each_entry_safe(page, tmp, compound_pagelist, lru) {
list_del(&page->lru);
release_pte_page(page);
}
}
static bool is_refcount_suitable(struct page *page)
{
int expected_refcount;
expected_refcount = total_mapcount(page);
if (PageSwapCache(page))
expected_refcount += compound_nr(page);
return page_count(page) == expected_refcount;
}
static int __collapse_huge_page_isolate(struct vm_area_struct *vma,
unsigned long address,
pte_t *pte,
struct list_head *compound_pagelist)
{
struct page *page = NULL;
pte_t *_pte;
int none_or_zero = 0, shared = 0, result = 0, referenced = 0;
bool writable = false;
for (_pte = pte; _pte < pte+HPAGE_PMD_NR;
_pte++, address += PAGE_SIZE) {
pte_t pteval = *_pte;
if (pte_none(pteval) || (pte_present(pteval) &&
is_zero_pfn(pte_pfn(pteval)))) {
if (!userfaultfd_armed(vma) &&
++none_or_zero <= khugepaged_max_ptes_none) {
continue;
} else {
result = SCAN_EXCEED_NONE_PTE;
goto out;
}
}
if (!pte_present(pteval)) {
result = SCAN_PTE_NON_PRESENT;
goto out;
}
page = vm_normal_page(vma, address, pteval);
if (unlikely(!page)) {
result = SCAN_PAGE_NULL;
goto out;
}
VM_BUG_ON_PAGE(!PageAnon(page), page);
if (page_mapcount(page) > 1 &&
++shared > khugepaged_max_ptes_shared) {
result = SCAN_EXCEED_SHARED_PTE;
goto out;
}
if (PageCompound(page)) {
struct page *p;
page = compound_head(page);
/*
* Check if we have dealt with the compound page
* already
*/
list_for_each_entry(p, compound_pagelist, lru) {
if (page == p)
goto next;
}
}
/*
* We can do it before isolate_lru_page because the
* page can't be freed from under us. NOTE: PG_lock
* is needed to serialize against split_huge_page
* when invoked from the VM.
*/
if (!trylock_page(page)) {
result = SCAN_PAGE_LOCK;
goto out;
}
/*
* Check if the page has any GUP (or other external) pins.
*
* The page table that maps the page has been already unlinked
* from the page table tree and this process cannot get
* an additional pin on the page.
*
* New pins can come later if the page is shared across fork,
* but not from this process. The other process cannot write to
* the page, only trigger CoW.
*/
if (!is_refcount_suitable(page)) {
unlock_page(page);
result = SCAN_PAGE_COUNT;
goto out;
}
if (!pte_write(pteval) && PageSwapCache(page) &&
!reuse_swap_page(page, NULL)) {
/*
* Page is in the swap cache and cannot be re-used.
* It cannot be collapsed into a THP.
*/
unlock_page(page);
result = SCAN_SWAP_CACHE_PAGE;
goto out;
}
/*
* Isolate the page to avoid collapsing an hugepage
* currently in use by the VM.
*/
if (isolate_lru_page(page)) {
unlock_page(page);
result = SCAN_DEL_PAGE_LRU;
goto out;
}
mod_node_page_state(page_pgdat(page),
NR_ISOLATED_ANON + page_is_file_lru(page),
compound_nr(page));
VM_BUG_ON_PAGE(!PageLocked(page), page);
VM_BUG_ON_PAGE(PageLRU(page), page);
if (PageCompound(page))
list_add_tail(&page->lru, compound_pagelist);
next:
/* There should be enough young pte to collapse the page */
if (pte_young(pteval) ||
page_is_young(page) || PageReferenced(page) ||
mmu_notifier_test_young(vma->vm_mm, address))
referenced++;
if (pte_write(pteval))
writable = true;
}
if (unlikely(!writable)) {
result = SCAN_PAGE_RO;
} else if (unlikely(!referenced)) {
result = SCAN_LACK_REFERENCED_PAGE;
} else {
result = SCAN_SUCCEED;
trace_mm_collapse_huge_page_isolate(page, none_or_zero,
referenced, writable, result);
return 1;
}
out:
release_pte_pages(pte, _pte, compound_pagelist);
trace_mm_collapse_huge_page_isolate(page, none_or_zero,
referenced, writable, result);
return 0;
}
static void __collapse_huge_page_copy(pte_t *pte, struct page *page,
struct vm_area_struct *vma,
unsigned long address,
spinlock_t *ptl,
struct list_head *compound_pagelist)
{
struct page *src_page, *tmp;
pte_t *_pte;
for (_pte = pte; _pte < pte + HPAGE_PMD_NR;
_pte++, page++, address += PAGE_SIZE) {
pte_t pteval = *_pte;
if (pte_none(pteval) || is_zero_pfn(pte_pfn(pteval))) {
clear_user_highpage(page, address);
add_mm_counter(vma->vm_mm, MM_ANONPAGES, 1);
if (is_zero_pfn(pte_pfn(pteval))) {
/*
* ptl mostly unnecessary.
*/
spin_lock(ptl);
/*
* paravirt calls inside pte_clear here are
* superfluous.
*/
pte_clear(vma->vm_mm, address, _pte);
spin_unlock(ptl);
}
} else {
src_page = pte_page(pteval);
copy_user_highpage(page, src_page, address, vma);
if (!PageCompound(src_page))
release_pte_page(src_page);
/*
* ptl mostly unnecessary, but preempt has to
* be disabled to update the per-cpu stats
* inside page_remove_rmap().
*/
spin_lock(ptl);
/*
* paravirt calls inside pte_clear here are
* superfluous.
*/
pte_clear(vma->vm_mm, address, _pte);
page_remove_rmap(src_page, false);
spin_unlock(ptl);
free_page_and_swap_cache(src_page);
}
}
list_for_each_entry_safe(src_page, tmp, compound_pagelist, lru) {
list_del(&src_page->lru);
release_pte_page(src_page);
}
}
static void khugepaged_alloc_sleep(void)
{
DEFINE_WAIT(wait);
add_wait_queue(&khugepaged_wait, &wait);
freezable_schedule_timeout_interruptible(
msecs_to_jiffies(khugepaged_alloc_sleep_millisecs));
remove_wait_queue(&khugepaged_wait, &wait);
}
static int khugepaged_node_load[MAX_NUMNODES];
static bool khugepaged_scan_abort(int nid)
{
int i;
/*
* If node_reclaim_mode is disabled, then no extra effort is made to
* allocate memory locally.
*/
if (!node_reclaim_enabled())
return false;
/* If there is a count for this node already, it must be acceptable */
if (khugepaged_node_load[nid])
return false;
for (i = 0; i < MAX_NUMNODES; i++) {
if (!khugepaged_node_load[i])
continue;
if (node_distance(nid, i) > node_reclaim_distance)
return true;
}
return false;
}
/* Defrag for khugepaged will enter direct reclaim/compaction if necessary */
static inline gfp_t alloc_hugepage_khugepaged_gfpmask(void)
{
return khugepaged_defrag() ? GFP_TRANSHUGE : GFP_TRANSHUGE_LIGHT;
}
#ifdef CONFIG_NUMA
static int khugepaged_find_target_node(void)
{
static int last_khugepaged_target_node = NUMA_NO_NODE;
int nid, target_node = 0, max_value = 0;
/* find first node with max normal pages hit */
for (nid = 0; nid < MAX_NUMNODES; nid++)
if (khugepaged_node_load[nid] > max_value) {
max_value = khugepaged_node_load[nid];
target_node = nid;
}
/* do some balance if several nodes have the same hit record */
if (target_node <= last_khugepaged_target_node)
for (nid = last_khugepaged_target_node + 1; nid < MAX_NUMNODES;
nid++)
if (max_value == khugepaged_node_load[nid]) {
target_node = nid;
break;
}
last_khugepaged_target_node = target_node;
return target_node;
}
static bool khugepaged_prealloc_page(struct page **hpage, bool *wait)
{
if (IS_ERR(*hpage)) {
if (!*wait)
return false;
*wait = false;
*hpage = NULL;
khugepaged_alloc_sleep();
} else if (*hpage) {
put_page(*hpage);
*hpage = NULL;
}
return true;
}
static struct page *
khugepaged_alloc_page(struct page **hpage, gfp_t gfp, int node)
{
VM_BUG_ON_PAGE(*hpage, *hpage);
*hpage = __alloc_pages_node(node, gfp, HPAGE_PMD_ORDER);
if (unlikely(!*hpage)) {
count_vm_event(THP_COLLAPSE_ALLOC_FAILED);
*hpage = ERR_PTR(-ENOMEM);
return NULL;
}
prep_transhuge_page(*hpage);
count_vm_event(THP_COLLAPSE_ALLOC);
return *hpage;
}
#else
static int khugepaged_find_target_node(void)
{
return 0;
}
static inline struct page *alloc_khugepaged_hugepage(void)
{
struct page *page;
page = alloc_pages(alloc_hugepage_khugepaged_gfpmask(),
HPAGE_PMD_ORDER);
if (page)
prep_transhuge_page(page);
return page;
}
static struct page *khugepaged_alloc_hugepage(bool *wait)
{
struct page *hpage;
do {
hpage = alloc_khugepaged_hugepage();
if (!hpage) {
count_vm_event(THP_COLLAPSE_ALLOC_FAILED);
if (!*wait)
return NULL;
*wait = false;
khugepaged_alloc_sleep();
} else
count_vm_event(THP_COLLAPSE_ALLOC);
} while (unlikely(!hpage) && likely(khugepaged_enabled()));
return hpage;
}
static bool khugepaged_prealloc_page(struct page **hpage, bool *wait)
{
/*
* If the hpage allocated earlier was briefly exposed in page cache
* before collapse_file() failed, it is possible that racing lookups
* have not yet completed, and would then be unpleasantly surprised by
* finding the hpage reused for the same mapping at a different offset.
* Just release the previous allocation if there is any danger of that.
*/
if (*hpage && page_count(*hpage) > 1) {
put_page(*hpage);
*hpage = NULL;
}
if (!*hpage)
*hpage = khugepaged_alloc_hugepage(wait);
if (unlikely(!*hpage))
return false;
return true;
}
static struct page *
khugepaged_alloc_page(struct page **hpage, gfp_t gfp, int node)
{
VM_BUG_ON(!*hpage);
return *hpage;
}
#endif
/*
* If mmap_lock temporarily dropped, revalidate vma
* before taking mmap_lock.
* Return 0 if succeeds, otherwise return none-zero
* value (scan code).
*/
static int hugepage_vma_revalidate(struct mm_struct *mm, unsigned long address,
struct vm_area_struct **vmap)
{
struct vm_area_struct *vma;
unsigned long hstart, hend;
if (unlikely(khugepaged_test_exit(mm)))
return SCAN_ANY_PROCESS;
*vmap = vma = find_vma(mm, address);
if (!vma)
return SCAN_VMA_NULL;
hstart = (vma->vm_start + ~HPAGE_PMD_MASK) & HPAGE_PMD_MASK;
hend = vma->vm_end & HPAGE_PMD_MASK;
if (address < hstart || address + HPAGE_PMD_SIZE > hend)
return SCAN_ADDRESS_RANGE;
if (!hugepage_vma_check(vma, vma->vm_flags))
return SCAN_VMA_CHECK;
/* Anon VMA expected */
if (!vma->anon_vma || vma->vm_ops)
return SCAN_VMA_CHECK;
return 0;
}
/*
* Bring missing pages in from swap, to complete THP collapse.
* Only done if khugepaged_scan_pmd believes it is worthwhile.
*
* Called and returns without pte mapped or spinlocks held,
* but with mmap_lock held to protect against vma changes.
*/
static bool __collapse_huge_page_swapin(struct mm_struct *mm,
struct vm_area_struct *vma,
unsigned long haddr, pmd_t *pmd,
int referenced)
{
int swapped_in = 0;
vm_fault_t ret = 0;
unsigned long address, end = haddr + (HPAGE_PMD_NR * PAGE_SIZE);
for (address = haddr; address < end; address += PAGE_SIZE) {
struct vm_fault vmf = {
.vma = vma,
.address = address,
.pgoff = linear_page_index(vma, haddr),
.flags = FAULT_FLAG_ALLOW_RETRY,
.pmd = pmd,
};
vmf.pte = pte_offset_map(pmd, address);
vmf.orig_pte = *vmf.pte;
if (!is_swap_pte(vmf.orig_pte)) {
pte_unmap(vmf.pte);
continue;
}
swapped_in++;
ret = do_swap_page(&vmf);
/* do_swap_page returns VM_FAULT_RETRY with released mmap_lock */
if (ret & VM_FAULT_RETRY) {
mmap_read_lock(mm);
if (hugepage_vma_revalidate(mm, haddr, &vma)) {
/* vma is no longer available, don't continue to swapin */
trace_mm_collapse_huge_page_swapin(mm, swapped_in, referenced, 0);
return false;
}
/* check if the pmd is still valid */
if (mm_find_pmd(mm, haddr) != pmd) {
trace_mm_collapse_huge_page_swapin(mm, swapped_in, referenced, 0);
return false;
}
}
if (ret & VM_FAULT_ERROR) {
trace_mm_collapse_huge_page_swapin(mm, swapped_in, referenced, 0);
return false;
}
}
/* Drain LRU add pagevec to remove extra pin on the swapped in pages */
if (swapped_in)
lru_add_drain();
trace_mm_collapse_huge_page_swapin(mm, swapped_in, referenced, 1);
return true;
}
static void collapse_huge_page(struct mm_struct *mm,
unsigned long address,
struct page **hpage,
int node, int referenced, int unmapped)
{
LIST_HEAD(compound_pagelist);
pmd_t *pmd, _pmd;
pte_t *pte;
pgtable_t pgtable;
struct page *new_page;
spinlock_t *pmd_ptl, *pte_ptl;
int isolated = 0, result = 0;
struct vm_area_struct *vma;
struct mmu_notifier_range range;
gfp_t gfp;
VM_BUG_ON(address & ~HPAGE_PMD_MASK);
/* Only allocate from the target node */
gfp = alloc_hugepage_khugepaged_gfpmask() | __GFP_THISNODE;
/*
* Before allocating the hugepage, release the mmap_lock read lock.
* The allocation can take potentially a long time if it involves
* sync compaction, and we do not need to hold the mmap_lock during
* that. We will recheck the vma after taking it again in write mode.
*/
mmap_read_unlock(mm);
new_page = khugepaged_alloc_page(hpage, gfp, node);
if (!new_page) {
result = SCAN_ALLOC_HUGE_PAGE_FAIL;
goto out_nolock;
}
if (unlikely(mem_cgroup_charge(new_page, mm, gfp))) {
result = SCAN_CGROUP_CHARGE_FAIL;
goto out_nolock;
}
count_memcg_page_event(new_page, THP_COLLAPSE_ALLOC);
mmap_read_lock(mm);
result = hugepage_vma_revalidate(mm, address, &vma);
if (result) {
mmap_read_unlock(mm);
goto out_nolock;
}
pmd = mm_find_pmd(mm, address);
if (!pmd) {
result = SCAN_PMD_NULL;
mmap_read_unlock(mm);
goto out_nolock;
}
/*
* __collapse_huge_page_swapin always returns with mmap_lock locked.
* If it fails, we release mmap_lock and jump out_nolock.
* Continuing to collapse causes inconsistency.
*/
if (unmapped && !__collapse_huge_page_swapin(mm, vma, address,
pmd, referenced)) {
mmap_read_unlock(mm);
goto out_nolock;
}
mmap_read_unlock(mm);
/*
* Prevent all access to pagetables with the exception of
* gup_fast later handled by the ptep_clear_flush and the VM
* handled by the anon_vma lock + PG_lock.
*/
mmap_write_lock(mm);
result = hugepage_vma_revalidate(mm, address, &vma);
if (result)
goto out_up_write;
/* check if the pmd is still valid */
if (mm_find_pmd(mm, address) != pmd)
goto out_up_write;
anon_vma_lock_write(vma->anon_vma);
mmu_notifier_range_init(&range, MMU_NOTIFY_CLEAR, 0, NULL, mm,
address, address + HPAGE_PMD_SIZE);
mmu_notifier_invalidate_range_start(&range);
pte = pte_offset_map(pmd, address);
pte_ptl = pte_lockptr(mm, pmd);
pmd_ptl = pmd_lock(mm, pmd); /* probably unnecessary */
/*
* After this gup_fast can't run anymore. This also removes
* any huge TLB entry from the CPU so we won't allow
* huge and small TLB entries for the same virtual address
* to avoid the risk of CPU bugs in that area.
*/
_pmd = pmdp_collapse_flush(vma, address, pmd);
spin_unlock(pmd_ptl);
mmu_notifier_invalidate_range_end(&range);
spin_lock(pte_ptl);
isolated = __collapse_huge_page_isolate(vma, address, pte,
&compound_pagelist);
spin_unlock(pte_ptl);
if (unlikely(!isolated)) {
pte_unmap(pte);
spin_lock(pmd_ptl);
BUG_ON(!pmd_none(*pmd));
/*
* We can only use set_pmd_at when establishing
* hugepmds and never for establishing regular pmds that
* points to regular pagetables. Use pmd_populate for that
*/
pmd_populate(mm, pmd, pmd_pgtable(_pmd));
spin_unlock(pmd_ptl);
anon_vma_unlock_write(vma->anon_vma);
result = SCAN_FAIL;
goto out_up_write;
}
/*
* All pages are isolated and locked so anon_vma rmap
* can't run anymore.
*/
anon_vma_unlock_write(vma->anon_vma);
__collapse_huge_page_copy(pte, new_page, vma, address, pte_ptl,
&compound_pagelist);
pte_unmap(pte);
/*
* spin_lock() below is not the equivalent of smp_wmb(), but
* the smp_wmb() inside __SetPageUptodate() can be reused to
* avoid the copy_huge_page writes to become visible after
* the set_pmd_at() write.
*/
__SetPageUptodate(new_page);
pgtable = pmd_pgtable(_pmd);
_pmd = mk_huge_pmd(new_page, vma->vm_page_prot);
_pmd = maybe_pmd_mkwrite(pmd_mkdirty(_pmd), vma);
spin_lock(pmd_ptl);
BUG_ON(!pmd_none(*pmd));
page_add_new_anon_rmap(new_page, vma, address, true);
lru_cache_add_inactive_or_unevictable(new_page, vma);
pgtable_trans_huge_deposit(mm, pmd, pgtable);
set_pmd_at(mm, address, pmd, _pmd);
update_mmu_cache_pmd(vma, address, pmd);
spin_unlock(pmd_ptl);
*hpage = NULL;
khugepaged_pages_collapsed++;
result = SCAN_SUCCEED;
out_up_write:
mmap_write_unlock(mm);
out_nolock:
if (!IS_ERR_OR_NULL(*hpage))
mem_cgroup_uncharge(*hpage);
trace_mm_collapse_huge_page(mm, isolated, result);
return;
}
static int khugepaged_scan_pmd(struct mm_struct *mm,
struct vm_area_struct *vma,
unsigned long address,
struct page **hpage)
{
pmd_t *pmd;
pte_t *pte, *_pte;
int ret = 0, result = 0, referenced = 0;
int none_or_zero = 0, shared = 0;
struct page *page = NULL;
unsigned long _address;
spinlock_t *ptl;
int node = NUMA_NO_NODE, unmapped = 0;
bool writable = false;
VM_BUG_ON(address & ~HPAGE_PMD_MASK);
pmd = mm_find_pmd(mm, address);
if (!pmd) {
result = SCAN_PMD_NULL;
goto out;
}
memset(khugepaged_node_load, 0, sizeof(khugepaged_node_load));
pte = pte_offset_map_lock(mm, pmd, address, &ptl);
for (_address = address, _pte = pte; _pte < pte+HPAGE_PMD_NR;
_pte++, _address += PAGE_SIZE) {
pte_t pteval = *_pte;
if (is_swap_pte(pteval)) {
if (++unmapped <= khugepaged_max_ptes_swap) {
/*
* Always be strict with uffd-wp
* enabled swap entries. Please see
* comment below for pte_uffd_wp().
*/
if (pte_swp_uffd_wp(pteval)) {
result = SCAN_PTE_UFFD_WP;
goto out_unmap;
}
continue;
} else {
result = SCAN_EXCEED_SWAP_PTE;
goto out_unmap;
}
}
if (pte_none(pteval) || is_zero_pfn(pte_pfn(pteval))) {
if (!userfaultfd_armed(vma) &&
++none_or_zero <= khugepaged_max_ptes_none) {
continue;
} else {
result = SCAN_EXCEED_NONE_PTE;
goto out_unmap;
}
}
if (pte_uffd_wp(pteval)) {
/*
* Don't collapse the page if any of the small
* PTEs are armed with uffd write protection.
* Here we can also mark the new huge pmd as
* write protected if any of the small ones is
* marked but that could bring unknown
* userfault messages that falls outside of
* the registered range. So, just be simple.
*/
result = SCAN_PTE_UFFD_WP;
goto out_unmap;
}
if (pte_write(pteval))
writable = true;
page = vm_normal_page(vma, _address, pteval);
if (unlikely(!page)) {
result = SCAN_PAGE_NULL;
goto out_unmap;
}
if (page_mapcount(page) > 1 &&
++shared > khugepaged_max_ptes_shared) {
result = SCAN_EXCEED_SHARED_PTE;
goto out_unmap;
}
page = compound_head(page);
/*
* Record which node the original page is from and save this
* information to khugepaged_node_load[].
* Khupaged will allocate hugepage from the node has the max
* hit record.
*/
node = page_to_nid(page);
if (khugepaged_scan_abort(node)) {
result = SCAN_SCAN_ABORT;
goto out_unmap;
}
khugepaged_node_load[node]++;
if (!PageLRU(page)) {
result = SCAN_PAGE_LRU;
goto out_unmap;
}
if (PageLocked(page)) {
result = SCAN_PAGE_LOCK;
goto out_unmap;
}
if (!PageAnon(page)) {
result = SCAN_PAGE_ANON;
goto out_unmap;
}
/*
* Check if the page has any GUP (or other external) pins.
*
* Here the check is racy it may see totmal_mapcount > refcount
* in some cases.
* For example, one process with one forked child process.
* The parent has the PMD split due to MADV_DONTNEED, then
* the child is trying unmap the whole PMD, but khugepaged
* may be scanning the parent between the child has
* PageDoubleMap flag cleared and dec the mapcount. So
* khugepaged may see total_mapcount > refcount.
*
* But such case is ephemeral we could always retry collapse
* later. However it may report false positive if the page
* has excessive GUP pins (i.e. 512). Anyway the same check
* will be done again later the risk seems low.
*/
if (!is_refcount_suitable(page)) {
result = SCAN_PAGE_COUNT;
goto out_unmap;
}
if (pte_young(pteval) ||
page_is_young(page) || PageReferenced(page) ||
mmu_notifier_test_young(vma->vm_mm, address))
referenced++;
}
if (!writable) {
result = SCAN_PAGE_RO;
} else if (!referenced || (unmapped && referenced < HPAGE_PMD_NR/2)) {
result = SCAN_LACK_REFERENCED_PAGE;
} else {
result = SCAN_SUCCEED;
ret = 1;
}
out_unmap:
pte_unmap_unlock(pte, ptl);
if (ret) {
node = khugepaged_find_target_node();
/* collapse_huge_page will return with the mmap_lock released */
collapse_huge_page(mm, address, hpage, node,
referenced, unmapped);
}
out:
trace_mm_khugepaged_scan_pmd(mm, page, writable, referenced,
none_or_zero, result, unmapped);
return ret;
}
static void collect_mm_slot(struct mm_slot *mm_slot)
{
struct mm_struct *mm = mm_slot->mm;
lockdep_assert_held(&khugepaged_mm_lock);
if (khugepaged_test_exit(mm)) {
/* free mm_slot */
hash_del(&mm_slot->hash);
list_del(&mm_slot->mm_node);
/*
* Not strictly needed because the mm exited already.
*
* clear_bit(MMF_VM_HUGEPAGE, &mm->flags);
*/
/* khugepaged_mm_lock actually not necessary for the below */
free_mm_slot(mm_slot);
mmdrop(mm);
}
}
#ifdef CONFIG_SHMEM
/*
* Notify khugepaged that given addr of the mm is pte-mapped THP. Then
* khugepaged should try to collapse the page table.
*/
static int khugepaged_add_pte_mapped_thp(struct mm_struct *mm,
unsigned long addr)
{
struct mm_slot *mm_slot;
VM_BUG_ON(addr & ~HPAGE_PMD_MASK);
spin_lock(&khugepaged_mm_lock);
mm_slot = get_mm_slot(mm);
if (likely(mm_slot && mm_slot->nr_pte_mapped_thp < MAX_PTE_MAPPED_THP))
mm_slot->pte_mapped_thp[mm_slot->nr_pte_mapped_thp++] = addr;
spin_unlock(&khugepaged_mm_lock);
return 0;
}
/**
* collapse_pte_mapped_thp - Try to collapse a pte-mapped THP for mm at
* address haddr.
*
* @mm: process address space where collapse happens
* @addr: THP collapse address
*
* This function checks whether all the PTEs in the PMD are pointing to the
* right THP. If so, retract the page table so the THP can refault in with
* as pmd-mapped.
*/
void collapse_pte_mapped_thp(struct mm_struct *mm, unsigned long addr)
{
unsigned long haddr = addr & HPAGE_PMD_MASK;
struct vm_area_struct *vma = find_vma(mm, haddr);
struct page *hpage;
pte_t *start_pte, *pte;
pmd_t *pmd, _pmd;
spinlock_t *ptl;
int count = 0;
int i;
if (!vma || !vma->vm_file ||
!range_in_vma(vma, haddr, haddr + HPAGE_PMD_SIZE))
return;
/*
* This vm_flags may not have VM_HUGEPAGE if the page was not
* collapsed by this mm. But we can still collapse if the page is
* the valid THP. Add extra VM_HUGEPAGE so hugepage_vma_check()
* will not fail the vma for missing VM_HUGEPAGE
*/
if (!hugepage_vma_check(vma, vma->vm_flags | VM_HUGEPAGE))
return;
hpage = find_lock_page(vma->vm_file->f_mapping,
linear_page_index(vma, haddr));
if (!hpage)
return;
if (!PageHead(hpage))
goto drop_hpage;
pmd = mm_find_pmd(mm, haddr);
if (!pmd)
goto drop_hpage;
start_pte = pte_offset_map_lock(mm, pmd, haddr, &ptl);
/* step 1: check all mapped PTEs are to the right huge page */
for (i = 0, addr = haddr, pte = start_pte;
i < HPAGE_PMD_NR; i++, addr += PAGE_SIZE, pte++) {
struct page *page;
/* empty pte, skip */
if (pte_none(*pte))
continue;
/* page swapped out, abort */
if (!pte_present(*pte))
goto abort;
page = vm_normal_page(vma, addr, *pte);
/*
* Note that uprobe, debugger, or MAP_PRIVATE may change the
* page table, but the new page will not be a subpage of hpage.
*/
if (hpage + i != page)
goto abort;
count++;
}
/* step 2: adjust rmap */
for (i = 0, addr = haddr, pte = start_pte;
i < HPAGE_PMD_NR; i++, addr += PAGE_SIZE, pte++) {
struct page *page;
if (pte_none(*pte))
continue;
page = vm_normal_page(vma, addr, *pte);
page_remove_rmap(page, false);
}
pte_unmap_unlock(start_pte, ptl);
/* step 3: set proper refcount and mm_counters. */
if (count) {
page_ref_sub(hpage, count);
add_mm_counter(vma->vm_mm, mm_counter_file(hpage), -count);
}
/* step 4: collapse pmd */
ptl = pmd_lock(vma->vm_mm, pmd);
_pmd = pmdp_collapse_flush(vma, haddr, pmd);
spin_unlock(ptl);
mm_dec_nr_ptes(mm);
pte_free(mm, pmd_pgtable(_pmd));
drop_hpage:
unlock_page(hpage);
put_page(hpage);
return;
abort:
pte_unmap_unlock(start_pte, ptl);
goto drop_hpage;
}
static void khugepaged_collapse_pte_mapped_thps(struct mm_slot *mm_slot)
{
struct mm_struct *mm = mm_slot->mm;
int i;
if (likely(mm_slot->nr_pte_mapped_thp == 0))
return;
if (!mmap_write_trylock(mm))
return;
if (unlikely(khugepaged_test_exit(mm)))
goto out;
for (i = 0; i < mm_slot->nr_pte_mapped_thp; i++)
collapse_pte_mapped_thp(mm, mm_slot->pte_mapped_thp[i]);
out:
mm_slot->nr_pte_mapped_thp = 0;
mmap_write_unlock(mm);
}
static void retract_page_tables(struct address_space *mapping, pgoff_t pgoff)
{
struct vm_area_struct *vma;
struct mm_struct *mm;
unsigned long addr;
pmd_t *pmd, _pmd;
i_mmap_lock_write(mapping);
vma_interval_tree_foreach(vma, &mapping->i_mmap, pgoff, pgoff) {
/*
* Check vma->anon_vma to exclude MAP_PRIVATE mappings that
* got written to. These VMAs are likely not worth investing
* mmap_write_lock(mm) as PMD-mapping is likely to be split
* later.
*
* Not that vma->anon_vma check is racy: it can be set up after
* the check but before we took mmap_lock by the fault path.
* But page lock would prevent establishing any new ptes of the
* page, so we are safe.
*
* An alternative would be drop the check, but check that page
* table is clear before calling pmdp_collapse_flush() under
* ptl. It has higher chance to recover THP for the VMA, but
* has higher cost too.
*/
if (vma->anon_vma)
continue;
addr = vma->vm_start + ((pgoff - vma->vm_pgoff) << PAGE_SHIFT);
if (addr & ~HPAGE_PMD_MASK)
continue;
if (vma->vm_end < addr + HPAGE_PMD_SIZE)
continue;
mm = vma->vm_mm;
pmd = mm_find_pmd(mm, addr);
if (!pmd)
continue;
/*
* We need exclusive mmap_lock to retract page table.
*
* We use trylock due to lock inversion: we need to acquire
* mmap_lock while holding page lock. Fault path does it in
* reverse order. Trylock is a way to avoid deadlock.
*/
if (mmap_write_trylock(mm)) {
if (!khugepaged_test_exit(mm)) {
spinlock_t *ptl = pmd_lock(mm, pmd);
/* assume page table is clear */
_pmd = pmdp_collapse_flush(vma, addr, pmd);
spin_unlock(ptl);
mm_dec_nr_ptes(mm);
pte_free(mm, pmd_pgtable(_pmd));
}
mmap_write_unlock(mm);
} else {
/* Try again later */
khugepaged_add_pte_mapped_thp(mm, addr);
}
}
i_mmap_unlock_write(mapping);
}
/**
* collapse_file - collapse filemap/tmpfs/shmem pages into huge one.
*
* @mm: process address space where collapse happens
* @file: file that collapse on
* @start: collapse start address
* @hpage: new allocated huge page for collapse
* @node: appointed node the new huge page allocate from
*
* Basic scheme is simple, details are more complex:
* - allocate and lock a new huge page;
* - scan page cache replacing old pages with the new one
* + swap/gup in pages if necessary;
* + fill in gaps;
* + keep old pages around in case rollback is required;
* - if replacing succeeds:
* + copy data over;
* + free old pages;
* + unlock huge page;
* - if replacing failed;
* + put all pages back and unfreeze them;
* + restore gaps in the page cache;
* + unlock and free huge page;
*/
static void collapse_file(struct mm_struct *mm,
struct file *file, pgoff_t start,
struct page **hpage, int node)
{
struct address_space *mapping = file->f_mapping;
gfp_t gfp;
struct page *new_page;
pgoff_t index, 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;
bool is_shmem = shmem_file(file);
int nr;
VM_BUG_ON(!IS_ENABLED(CONFIG_READ_ONLY_THP_FOR_FS) && !is_shmem);
VM_BUG_ON(start & (HPAGE_PMD_NR - 1));
/* Only allocate from the target node */
gfp = alloc_hugepage_khugepaged_gfpmask() | __GFP_THISNODE;
new_page = khugepaged_alloc_page(hpage, gfp, node);
if (!new_page) {
result = SCAN_ALLOC_HUGE_PAGE_FAIL;
goto out;
}
if (unlikely(mem_cgroup_charge(new_page, mm, gfp))) {
result = SCAN_CGROUP_CHARGE_FAIL;
goto out;
}
count_memcg_page_event(new_page, THP_COLLAPSE_ALLOC);
/* This will be less messy when we use multi-index entries */
do {
xas_lock_irq(&xas);
xas_create_range(&xas);
if (!xas_error(&xas))
break;
xas_unlock_irq(&xas);
if (!xas_nomem(&xas, GFP_KERNEL)) {
result = SCAN_FAIL;
goto out;
}
} while (1);
__SetPageLocked(new_page);
if (is_shmem)
__SetPageSwapBacked(new_page);
new_page->index = start;
new_page->mapping = mapping;
/*
* At this point the new_page is locked and not up-to-date.
* It's safe to insert it into the page cache, because nobody would
* be able to map it or use it in another way until we unlock it.
*/
xas_set(&xas, start);
for (index = start; index < end; index++) {
struct page *page = xas_next(&xas);
VM_BUG_ON(index != xas.xa_index);
if (is_shmem) {
if (!page) {
/*
* Stop if extent has been truncated or
* hole-punched, and is now completely
* empty.
*/
if (index == start) {
if (!xas_next_entry(&xas, end - 1)) {
result = SCAN_TRUNCATED;
goto xa_locked;
}
xas_set(&xas, index);
}
if (!shmem_charge(mapping->host, 1)) {
result = SCAN_FAIL;
goto xa_locked;
}
xas_store(&xas, new_page);
nr_none++;
continue;
}
if (xa_is_value(page) || !PageUptodate(page)) {
xas_unlock_irq(&xas);
/* swap in or instantiate fallocated page */
if (shmem_getpage(mapping->host, index, &page,
SGP_NOALLOC)) {
result = SCAN_FAIL;
goto xa_unlocked;
}
} else if (trylock_page(page)) {
get_page(page);
xas_unlock_irq(&xas);
} else {
result = SCAN_PAGE_LOCK;
goto xa_locked;
}
} else { /* !is_shmem */
if (!page || xa_is_value(page)) {
xas_unlock_irq(&xas);
page_cache_sync_readahead(mapping, &file->f_ra,
file, index,
end - index);
/* drain pagevecs to help isolate_lru_page() */
lru_add_drain();
page = find_lock_page(mapping, index);
if (unlikely(page == NULL)) {
result = SCAN_FAIL;
goto xa_unlocked;
}
} else if (PageDirty(page)) {
/*
* khugepaged only works on read-only fd,
* so this page is dirty because it hasn't
* been flushed since first write. There
* won't be new dirty pages.
*
* Trigger async flush here and hope the
* writeback is done when khugepaged
* revisits this page.
*
* This is a one-off situation. We are not
* forcing writeback in loop.
*/
xas_unlock_irq(&xas);
filemap_flush(mapping);
result = SCAN_FAIL;
goto xa_unlocked;
} else if (PageWriteback(page)) {
xas_unlock_irq(&xas);
result = SCAN_FAIL;
goto xa_unlocked;
} else if (trylock_page(page)) {
get_page(page);
xas_unlock_irq(&xas);
} else {
result = SCAN_PAGE_LOCK;
goto xa_locked;
}
}
/*
* The page must be locked, so we can drop the i_pages lock
* without racing with truncate.
*/
VM_BUG_ON_PAGE(!PageLocked(page), page);
/* make sure the page is up to date */
if (unlikely(!PageUptodate(page))) {
result = SCAN_FAIL;
goto out_unlock;
}
/*
* If file was truncated then extended, or hole-punched, before
* we locked the first page, then a THP might be there already.
*/
if (PageTransCompound(page)) {
result = SCAN_PAGE_COMPOUND;
goto out_unlock;
}
if (page_mapping(page) != mapping) {
result = SCAN_TRUNCATED;
goto out_unlock;
}
if (!is_shmem && (PageDirty(page) ||
PageWriteback(page))) {
/*
* khugepaged only works on read-only fd, so this
* page is dirty because it hasn't been flushed
* since first write.
*/
result = SCAN_FAIL;
goto out_unlock;
}
if (isolate_lru_page(page)) {
result = SCAN_DEL_PAGE_LRU;
goto out_unlock;
}
if (page_has_private(page) &&
!try_to_release_page(page, GFP_KERNEL)) {
result = SCAN_PAGE_HAS_PRIVATE;
putback_lru_page(page);
goto out_unlock;
}
if (page_mapped(page))
unmap_mapping_pages(mapping, index, 1, false);
xas_lock_irq(&xas);
xas_set(&xas, index);
VM_BUG_ON_PAGE(page != xas_load(&xas), page);
VM_BUG_ON_PAGE(page_mapped(page), page);
/*
* The page is expected to have page_count() == 3:
* - we hold a pin on it;
* - one reference from page cache;
* - one from isolate_lru_page;
*/
if (!page_ref_freeze(page, 3)) {
result = SCAN_PAGE_COUNT;
xas_unlock_irq(&xas);
putback_lru_page(page);
goto out_unlock;
}
/*
* Add the page to the list to be able to undo the collapse if
* something go wrong.
*/
list_add_tail(&page->lru, &pagelist);
/* Finally, replace with the new page. */
xas_store(&xas, new_page);
continue;
out_unlock:
unlock_page(page);
put_page(page);
goto xa_unlocked;
}
nr = thp_nr_pages(new_page);
if (is_shmem)
__mod_lruvec_page_state(new_page, NR_SHMEM_THPS, nr);
else {
__mod_lruvec_page_state(new_page, NR_FILE_THPS, nr);
filemap_nr_thps_inc(mapping);
/*
* Paired with smp_mb() in do_dentry_open() to ensure
* i_writecount is up to date and the update to nr_thps is
* visible. Ensures the page cache will be truncated if the
* file is opened writable.
*/
smp_mb();
if (inode_is_open_for_write(mapping->host)) {
result = SCAN_FAIL;
__mod_lruvec_page_state(new_page, NR_FILE_THPS, -nr);
filemap_nr_thps_dec(mapping);
goto xa_locked;
}
}
if (nr_none) {
__mod_lruvec_page_state(new_page, NR_FILE_PAGES, nr_none);
if (is_shmem)
__mod_lruvec_page_state(new_page, NR_SHMEM, nr_none);
}
xa_locked:
xas_unlock_irq(&xas);
xa_unlocked:
if (result == SCAN_SUCCEED) {
struct page *page, *tmp;
/*
* Replacing old pages with new one has succeeded, now we
* need to copy the content and free the old pages.
*/
index = start;
list_for_each_entry_safe(page, tmp, &pagelist, lru) {
while (index < page->index) {
clear_highpage(new_page + (index % HPAGE_PMD_NR));
index++;
}
copy_highpage(new_page + (page->index % HPAGE_PMD_NR),
page);
list_del(&page->lru);
page->mapping = NULL;
page_ref_unfreeze(page, 1);
ClearPageActive(page);
ClearPageUnevictable(page);
unlock_page(page);
put_page(page);
index++;
}
while (index < end) {
clear_highpage(new_page + (index % HPAGE_PMD_NR));
index++;
}
SetPageUptodate(new_page);
page_ref_add(new_page, HPAGE_PMD_NR - 1);
if (is_shmem)
set_page_dirty(new_page);
lru_cache_add(new_page);
/*
* Remove pte page tables, so we can re-fault the page as huge.
*/
retract_page_tables(mapping, start);
*hpage = NULL;
khugepaged_pages_collapsed++;
} else {
struct page *page;
/* Something went wrong: roll back page cache changes */
xas_lock_irq(&xas);
mapping->nrpages -= nr_none;
if (is_shmem)
shmem_uncharge(mapping->host, nr_none);
xas_set(&xas, start);
xas_for_each(&xas, page, end - 1) {
page = list_first_entry_or_null(&pagelist,
struct page, lru);
if (!page || xas.xa_index < page->index) {
if (!nr_none)
break;
nr_none--;
/* Put holes back where they were */
xas_store(&xas, NULL);
continue;
}
VM_BUG_ON_PAGE(page->index != xas.xa_index, page);
/* Unfreeze the page. */
list_del(&page->lru);
page_ref_unfreeze(page, 2);
xas_store(&xas, page);
xas_pause(&xas);
xas_unlock_irq(&xas);
unlock_page(page);
putback_lru_page(page);
xas_lock_irq(&xas);
}
VM_BUG_ON(nr_none);
xas_unlock_irq(&xas);
new_page->mapping = NULL;
}
unlock_page(new_page);
out:
VM_BUG_ON(!list_empty(&pagelist));
if (!IS_ERR_OR_NULL(*hpage))
mem_cgroup_uncharge(*hpage);
/* TODO: tracepoints */
}
static void khugepaged_scan_file(struct mm_struct *mm,
struct file *file, pgoff_t start, struct page **hpage)
{
struct page *page = 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;
present = 0;
swap = 0;
memset(khugepaged_node_load, 0, sizeof(khugepaged_node_load));
rcu_read_lock();
xas_for_each(&xas, page, start + HPAGE_PMD_NR - 1) {
if (xas_retry(&xas, page))
continue;
if (xa_is_value(page)) {
if (++swap > khugepaged_max_ptes_swap) {
result = SCAN_EXCEED_SWAP_PTE;
break;
}
continue;
}
if (PageTransCompound(page)) {
result = SCAN_PAGE_COMPOUND;
break;
}
node = page_to_nid(page);
if (khugepaged_scan_abort(node)) {
result = SCAN_SCAN_ABORT;
break;
}
khugepaged_node_load[node]++;
if (!PageLRU(page)) {
result = SCAN_PAGE_LRU;
break;
}
if (page_count(page) !=
1 + page_mapcount(page) + page_has_private(page)) {
result = SCAN_PAGE_COUNT;
break;
}
/*
* We probably should check if the page is referenced here, but
* nobody would transfer pte_young() to PageReferenced() for us.
* And rmap walk here is just too costly...
*/
present++;
if (need_resched()) {
xas_pause(&xas);
cond_resched_rcu();
}
}
rcu_read_unlock();
if (result == SCAN_SUCCEED) {
if (present < HPAGE_PMD_NR - khugepaged_max_ptes_none) {
result = SCAN_EXCEED_NONE_PTE;
} else {
node = khugepaged_find_target_node();
collapse_file(mm, file, start, hpage, node);
}
}
/* TODO: tracepoints */
}
#else
static void khugepaged_scan_file(struct mm_struct *mm,
struct file *file, pgoff_t start, struct page **hpage)
{
BUILD_BUG();
}
static void khugepaged_collapse_pte_mapped_thps(struct mm_slot *mm_slot)
{
}
#endif
static unsigned int khugepaged_scan_mm_slot(unsigned int pages,
struct page **hpage)
__releases(&khugepaged_mm_lock)
__acquires(&khugepaged_mm_lock)
{
struct mm_slot *mm_slot;
struct mm_struct *mm;
struct vm_area_struct *vma;
int progress = 0;
VM_BUG_ON(!pages);
lockdep_assert_held(&khugepaged_mm_lock);
if (khugepaged_scan.mm_slot)
mm_slot = khugepaged_scan.mm_slot;
else {
mm_slot = list_entry(khugepaged_scan.mm_head.next,
struct mm_slot, mm_node);
khugepaged_scan.address = 0;
khugepaged_scan.mm_slot = mm_slot;
}
spin_unlock(&khugepaged_mm_lock);
khugepaged_collapse_pte_mapped_thps(mm_slot);
mm = mm_slot->mm;
/*
* Don't wait for semaphore (to avoid long wait times). Just move to
* the next mm on the list.
*/
vma = NULL;
if (unlikely(!mmap_read_trylock(mm)))
goto breakouterloop_mmap_lock;
if (likely(!khugepaged_test_exit(mm)))
vma = find_vma(mm, khugepaged_scan.address);
progress++;
for (; vma; vma = vma->vm_next) {
unsigned long hstart, hend;
cond_resched();
if (unlikely(khugepaged_test_exit(mm))) {
progress++;
break;
}
if (!hugepage_vma_check(vma, vma->vm_flags)) {
skip:
progress++;
continue;
}
hstart = (vma->vm_start + ~HPAGE_PMD_MASK) & HPAGE_PMD_MASK;
hend = vma->vm_end & HPAGE_PMD_MASK;
if (hstart >= hend)
goto skip;
if (khugepaged_scan.address > hend)
goto skip;
if (khugepaged_scan.address < hstart)
khugepaged_scan.address = hstart;
VM_BUG_ON(khugepaged_scan.address & ~HPAGE_PMD_MASK);
if (shmem_file(vma->vm_file) && !shmem_huge_enabled(vma))
goto skip;
while (khugepaged_scan.address < hend) {
int ret;
cond_resched();
if (unlikely(khugepaged_test_exit(mm)))
goto breakouterloop;
VM_BUG_ON(khugepaged_scan.address < hstart ||
khugepaged_scan.address + HPAGE_PMD_SIZE >
hend);
if (IS_ENABLED(CONFIG_SHMEM) && vma->vm_file) {
struct file *file = get_file(vma->vm_file);
pgoff_t pgoff = linear_page_index(vma,
khugepaged_scan.address);
mmap_read_unlock(mm);
ret = 1;
khugepaged_scan_file(mm, file, pgoff, hpage);
fput(file);
} else {
ret = khugepaged_scan_pmd(mm, vma,
khugepaged_scan.address,
hpage);
}
/* move to next address */
khugepaged_scan.address += HPAGE_PMD_SIZE;
progress += HPAGE_PMD_NR;
if (ret)
/* we released mmap_lock so break loop */
goto breakouterloop_mmap_lock;
if (progress >= pages)
goto breakouterloop;
}
}
breakouterloop:
mmap_read_unlock(mm); /* exit_mmap will destroy ptes after this */
breakouterloop_mmap_lock:
spin_lock(&khugepaged_mm_lock);
VM_BUG_ON(khugepaged_scan.mm_slot != mm_slot);
/*
* Release the current mm_slot if this mm is about to die, or
* if we scanned all vmas of this mm.
*/
if (khugepaged_test_exit(mm) || !vma) {
/*
* Make sure that if mm_users is reaching zero while
* khugepaged runs here, khugepaged_exit will find
* mm_slot not pointing to the exiting mm.
*/
if (mm_slot->mm_node.next != &khugepaged_scan.mm_head) {
khugepaged_scan.mm_slot = list_entry(
mm_slot->mm_node.next,
struct mm_slot, mm_node);
khugepaged_scan.address = 0;
} else {
khugepaged_scan.mm_slot = NULL;
khugepaged_full_scans++;
}
collect_mm_slot(mm_slot);
}
return progress;
}
static int khugepaged_has_work(void)
{
return !list_empty(&khugepaged_scan.mm_head) &&
khugepaged_enabled();
}
static int khugepaged_wait_event(void)
{
return !list_empty(&khugepaged_scan.mm_head) ||
kthread_should_stop();
}
static void khugepaged_do_scan(void)
{
struct page *hpage = NULL;
unsigned int progress = 0, pass_through_head = 0;
unsigned int pages = READ_ONCE(khugepaged_pages_to_scan);
bool wait = true;
lru_add_drain_all();
while (progress < pages) {
if (!khugepaged_prealloc_page(&hpage, &wait))
break;
cond_resched();
if (unlikely(kthread_should_stop() || try_to_freeze()))
break;
spin_lock(&khugepaged_mm_lock);
if (!khugepaged_scan.mm_slot)
pass_through_head++;
if (khugepaged_has_work() &&
pass_through_head < 2)
progress += khugepaged_scan_mm_slot(pages - progress,
&hpage);
else
progress = pages;
spin_unlock(&khugepaged_mm_lock);
}
if (!IS_ERR_OR_NULL(hpage))
put_page(hpage);
}
static bool khugepaged_should_wakeup(void)
{
return kthread_should_stop() ||
time_after_eq(jiffies, khugepaged_sleep_expire);
}
static void khugepaged_wait_work(void)
{
if (khugepaged_has_work()) {
const unsigned long scan_sleep_jiffies =
msecs_to_jiffies(khugepaged_scan_sleep_millisecs);
if (!scan_sleep_jiffies)
return;
khugepaged_sleep_expire = jiffies + scan_sleep_jiffies;
wait_event_freezable_timeout(khugepaged_wait,
khugepaged_should_wakeup(),
scan_sleep_jiffies);
return;
}
if (khugepaged_enabled())
wait_event_freezable(khugepaged_wait, khugepaged_wait_event());
}
static int khugepaged(void *none)
{
struct mm_slot *mm_slot;
set_freezable();
set_user_nice(current, MAX_NICE);
while (!kthread_should_stop()) {
khugepaged_do_scan();
khugepaged_wait_work();
}
spin_lock(&khugepaged_mm_lock);
mm_slot = khugepaged_scan.mm_slot;
khugepaged_scan.mm_slot = NULL;
if (mm_slot)
collect_mm_slot(mm_slot);
spin_unlock(&khugepaged_mm_lock);
return 0;
}
static void set_recommended_min_free_kbytes(void)
{
struct zone *zone;
int nr_zones = 0;
unsigned long recommended_min;
for_each_populated_zone(zone) {
/*
* We don't need to worry about fragmentation of
* ZONE_MOVABLE since it only has movable pages.
*/
if (zone_idx(zone) > gfp_zone(GFP_USER))
continue;
nr_zones++;
}
/* Ensure 2 pageblocks are free to assist fragmentation avoidance */
recommended_min = pageblock_nr_pages * nr_zones * 2;
/*
* Make sure that on average at least two pageblocks are almost free
* of another type, one for a migratetype to fall back to and a
* second to avoid subsequent fallbacks of other types There are 3
* MIGRATE_TYPES we care about.
*/
recommended_min += pageblock_nr_pages * nr_zones *
MIGRATE_PCPTYPES * MIGRATE_PCPTYPES;
/* don't ever allow to reserve more than 5% of the lowmem */
recommended_min = min(recommended_min,
(unsigned long) nr_free_buffer_pages() / 20);
recommended_min <<= (PAGE_SHIFT-10);
if (recommended_min > min_free_kbytes) {
if (user_min_free_kbytes >= 0)
pr_info("raising min_free_kbytes from %d to %lu to help transparent hugepage allocations\n",
min_free_kbytes, recommended_min);
min_free_kbytes = recommended_min;
}
setup_per_zone_wmarks();
}
int start_stop_khugepaged(void)
{
int err = 0;
mutex_lock(&khugepaged_mutex);
if (khugepaged_enabled()) {
if (!khugepaged_thread)
khugepaged_thread = kthread_run(khugepaged, NULL,
"khugepaged");
if (IS_ERR(khugepaged_thread)) {
pr_err("khugepaged: kthread_run(khugepaged) failed\n");
err = PTR_ERR(khugepaged_thread);
khugepaged_thread = NULL;
goto fail;
}
if (!list_empty(&khugepaged_scan.mm_head))
wake_up_interruptible(&khugepaged_wait);
set_recommended_min_free_kbytes();
} else if (khugepaged_thread) {
kthread_stop(khugepaged_thread);
khugepaged_thread = NULL;
}
fail:
mutex_unlock(&khugepaged_mutex);
return err;
}
void khugepaged_min_free_kbytes_update(void)
{
mutex_lock(&khugepaged_mutex);
if (khugepaged_enabled() && khugepaged_thread)
set_recommended_min_free_kbytes();
mutex_unlock(&khugepaged_mutex);
}