linux/mm/khugepaged.c
Kirill A. Shutemov 9445689f3b khugepaged: allow to collapse a page shared across fork
The page can be included into collapse as long as it doesn't have extra
pins (from GUP or otherwise).

Logic to check the refcount is moved to a separate function.  For pages in
swap cache, add compound_nr(page) to the expected refcount, in order to
handle the compound page case.  This is in preparation for the following
patch.

VM_BUG_ON_PAGE() was removed from __collapse_huge_page_copy() as the
invariant it checks is no longer valid: the source can be mapped multiple
times now.

[yang.shi@linux.alibaba.com: remove error message when checking external pins]
  Link: http://lkml.kernel.org/r/1589317383-9595-1-git-send-email-yang.shi@linux.alibaba.com
[cai@lca.pw: fix set-but-not-used warning]
  Link: http://lkml.kernel.org/r/20200521145644.GA6367@ovpn-112-192.phx2.redhat.com
Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Signed-off-by: Yang Shi <yang.shi@linux.alibaba.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Tested-by: Zi Yan <ziy@nvidia.com>
Reviewed-by: William Kucharski <william.kucharski@oracle.com>
Reviewed-by: Zi Yan <ziy@nvidia.com>
Reviewed-by: John Hubbard <jhubbard@nvidia.com>
Acked-by: Yang Shi <yang.shi@linux.alibaba.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Ralph Campbell <rcampbell@nvidia.com>
Link: http://lkml.kernel.org/r/20200416160026.16538-6-kirill.shutemov@linux.intel.com
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-06-03 20:09:46 -07:00

2263 lines
56 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_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_EXCEED_SWAP_PTE,
SCAN_TRUNCATED,
SCAN_PAGE_HAS_PRIVATE,
};
#define CREATE_TRACE_POINTS
#include <trace/events/huge_memory.h>
/* 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;
#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
*/
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 sprintf(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 long msecs;
int err;
err = kstrtoul(buf, 10, &msecs);
if (err || msecs > UINT_MAX)
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 sprintf(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 long msecs;
int err;
err = kstrtoul(buf, 10, &msecs);
if (err || msecs > UINT_MAX)
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 sprintf(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)
{
int err;
unsigned long pages;
err = kstrtoul(buf, 10, &pages);
if (err || !pages || pages > UINT_MAX)
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 sprintf(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 sprintf(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 sprintf(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 sprintf(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 struct attribute *khugepaged_attr[] = {
&khugepaged_defrag_attr.attr,
&khugepaged_max_ptes_none_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,
&khugepaged_max_ptes_swap_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;
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 ((!(vm_flags & VM_HUGEPAGE) && !khugepaged_always()) ||
(vm_flags & VM_NOHUGEPAGE) ||
test_bit(MMF_DISABLE_THP, &vma->vm_mm->flags))
return false;
if (shmem_file(vma->vm_file) ||
(IS_ENABLED(CONFIG_READ_ONLY_THP_FOR_FS) &&
vma->vm_file &&
(vm_flags & VM_DENYWRITE))) {
return IS_ALIGNED((vma->vm_start >> PAGE_SHIFT) - vma->vm_pgoff,
HPAGE_PMD_NR);
}
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_sem.
*/
down_write(&mm->mmap_sem);
up_write(&mm->mmap_sem);
}
}
static void release_pte_page(struct page *page)
{
dec_node_page_state(page, NR_ISOLATED_ANON + page_is_file_lru(page));
unlock_page(page);
putback_lru_page(page);
}
static void release_pte_pages(pte_t *pte, pte_t *_pte)
{
while (--_pte >= pte) {
pte_t pteval = *_pte;
if (!pte_none(pteval) && !is_zero_pfn(pte_pfn(pteval)))
release_pte_page(pte_page(pteval));
}
}
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 page *page = NULL;
pte_t *_pte;
int none_or_zero = 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;
}
/* TODO: teach khugepaged to collapse THP mapped with pte */
if (PageCompound(page)) {
result = SCAN_PAGE_COMPOUND;
goto out;
}
VM_BUG_ON_PAGE(!PageAnon(page), page);
/*
* 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 additinal 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)) {
writable = true;
} else {
if (PageSwapCache(page) &&
!reuse_swap_page(page, NULL)) {
unlock_page(page);
result = SCAN_SWAP_CACHE_PAGE;
goto out;
}
/*
* Page is not in the swap cache. It can be collapsed
* into a THP.
*/
}
/*
* 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;
}
inc_node_page_state(page,
NR_ISOLATED_ANON + page_is_file_lru(page));
VM_BUG_ON_PAGE(!PageLocked(page), page);
VM_BUG_ON_PAGE(PageLRU(page), page);
/* 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 (likely(writable)) {
if (likely(referenced)) {
result = SCAN_SUCCEED;
trace_mm_collapse_huge_page_isolate(page, none_or_zero,
referenced, writable, result);
return 1;
}
} else {
result = SCAN_PAGE_RO;
}
out:
release_pte_pages(pte, _pte);
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)
{
pte_t *_pte;
for (_pte = pte; _pte < pte + HPAGE_PMD_NR;
_pte++, page++, address += PAGE_SIZE) {
pte_t pteval = *_pte;
struct page *src_page;
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);
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);
}
}
}
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_mode)
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 (!*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_sem temporarily dropped, revalidate vma
* before taking mmap_sem.
* 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;
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_sem held to protect against vma changes.
*/
static bool __collapse_huge_page_swapin(struct mm_struct *mm,
struct vm_area_struct *vma,
unsigned long address, pmd_t *pmd,
int referenced)
{
int swapped_in = 0;
vm_fault_t ret = 0;
struct vm_fault vmf = {
.vma = vma,
.address = address,
.flags = FAULT_FLAG_ALLOW_RETRY,
.pmd = pmd,
.pgoff = linear_page_index(vma, address),
};
vmf.pte = pte_offset_map(pmd, address);
for (; vmf.address < address + HPAGE_PMD_NR*PAGE_SIZE;
vmf.pte++, vmf.address += PAGE_SIZE) {
vmf.orig_pte = *vmf.pte;
if (!is_swap_pte(vmf.orig_pte))
continue;
swapped_in++;
ret = do_swap_page(&vmf);
/* do_swap_page returns VM_FAULT_RETRY with released mmap_sem */
if (ret & VM_FAULT_RETRY) {
down_read(&mm->mmap_sem);
if (hugepage_vma_revalidate(mm, address, &vmf.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, address) != 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;
}
/* pte is unmapped now, we need to map it */
vmf.pte = pte_offset_map(pmd, vmf.address);
}
vmf.pte--;
pte_unmap(vmf.pte);
/* 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)
{
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 mem_cgroup *memcg;
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_sem read lock.
* The allocation can take potentially a long time if it involves
* sync compaction, and we do not need to hold the mmap_sem during
* that. We will recheck the vma after taking it again in write mode.
*/
up_read(&mm->mmap_sem);
new_page = khugepaged_alloc_page(hpage, gfp, node);
if (!new_page) {
result = SCAN_ALLOC_HUGE_PAGE_FAIL;
goto out_nolock;
}
if (unlikely(mem_cgroup_try_charge(new_page, mm, gfp, &memcg, true))) {
result = SCAN_CGROUP_CHARGE_FAIL;
goto out_nolock;
}
down_read(&mm->mmap_sem);
result = hugepage_vma_revalidate(mm, address, &vma);
if (result) {
mem_cgroup_cancel_charge(new_page, memcg, true);
up_read(&mm->mmap_sem);
goto out_nolock;
}
pmd = mm_find_pmd(mm, address);
if (!pmd) {
result = SCAN_PMD_NULL;
mem_cgroup_cancel_charge(new_page, memcg, true);
up_read(&mm->mmap_sem);
goto out_nolock;
}
/*
* __collapse_huge_page_swapin always returns with mmap_sem locked.
* If it fails, we release mmap_sem and jump out_nolock.
* Continuing to collapse causes inconsistency.
*/
if (unmapped && !__collapse_huge_page_swapin(mm, vma, address,
pmd, referenced)) {
mem_cgroup_cancel_charge(new_page, memcg, true);
up_read(&mm->mmap_sem);
goto out_nolock;
}
up_read(&mm->mmap_sem);
/*
* 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.
*/
down_write(&mm->mmap_sem);
result = SCAN_ANY_PROCESS;
if (!mmget_still_valid(mm))
goto out;
result = hugepage_vma_revalidate(mm, address, &vma);
if (result)
goto out;
/* check if the pmd is still valid */
if (mm_find_pmd(mm, address) != pmd)
goto out;
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);
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;
}
/*
* 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);
pte_unmap(pte);
__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() below is not the equivalent of smp_wmb(), so
* this is needed to avoid the copy_huge_page writes to become
* visible after the set_pmd_at() write.
*/
smp_wmb();
spin_lock(pmd_ptl);
BUG_ON(!pmd_none(*pmd));
page_add_new_anon_rmap(new_page, vma, address, true);
mem_cgroup_commit_charge(new_page, memcg, false, true);
count_memcg_events(memcg, THP_COLLAPSE_ALLOC, 1);
lru_cache_add_active_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:
up_write(&mm->mmap_sem);
out_nolock:
trace_mm_collapse_huge_page(mm, isolated, result);
return;
out:
mem_cgroup_cancel_charge(new_page, memcg, true);
goto out_up_write;
}
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, none_or_zero = 0, result = 0, referenced = 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_present(pteval)) {
result = SCAN_PTE_NON_PRESENT;
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 uknown
* 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;
}
/* TODO: teach khugepaged to collapse THP mapped with pte */
if (PageCompound(page)) {
result = SCAN_PAGE_COMPOUND;
goto out_unmap;
}
/*
* 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_sem 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;
}
/**
* Try to collapse a pte-mapped THP for mm at address haddr.
*
* 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 = NULL;
pte_t *start_pte, *pte;
pmd_t *pmd, _pmd;
spinlock_t *ptl;
int count = 0;
int i;
if (!vma || !vma->vm_file ||
vma->vm_start > haddr || vma->vm_end < 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;
pmd = mm_find_pmd(mm, haddr);
if (!pmd)
return;
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);
if (!page || !PageCompound(page))
goto abort;
if (!hpage) {
hpage = compound_head(page);
/*
* The mapping of the THP should not change.
*
* Note that uprobe, debugger, or MAP_PRIVATE may
* change the page table, but the new page will
* not pass PageCompound() check.
*/
if (WARN_ON(hpage->mapping != vma->vm_file->f_mapping))
goto abort;
}
/*
* Confirm the page maps to the correct subpage.
*
* Note that uprobe, debugger, or MAP_PRIVATE may change
* the page table, but the new page will not pass
* PageCompound() check.
*/
if (WARN_ON(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 (hpage) {
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, addr, pmd);
spin_unlock(ptl);
mm_dec_nr_ptes(mm);
pte_free(mm, pmd_pgtable(_pmd));
return;
abort:
pte_unmap_unlock(start_pte, ptl);
}
static int 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 0;
if (!down_write_trylock(&mm->mmap_sem))
return -EBUSY;
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;
up_write(&mm->mmap_sem);
return 0;
}
static void retract_page_tables(struct address_space *mapping, pgoff_t pgoff)
{
struct vm_area_struct *vma;
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
* down_write(mmap_sem) 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_sem 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;
pmd = mm_find_pmd(vma->vm_mm, addr);
if (!pmd)
continue;
/*
* We need exclusive mmap_sem to retract page table.
*
* We use trylock due to lock inversion: we need to acquire
* mmap_sem while holding page lock. Fault path does it in
* reverse order. Trylock is a way to avoid deadlock.
*/
if (down_write_trylock(&vma->vm_mm->mmap_sem)) {
spinlock_t *ptl = pmd_lock(vma->vm_mm, pmd);
/* assume page table is clear */
_pmd = pmdp_collapse_flush(vma, addr, pmd);
spin_unlock(ptl);
up_write(&vma->vm_mm->mmap_sem);
mm_dec_nr_ptes(vma->vm_mm);
pte_free(vma->vm_mm, pmd_pgtable(_pmd));
} else {
/* Try again later */
khugepaged_add_pte_mapped_thp(vma->vm_mm, addr);
}
}
i_mmap_unlock_write(mapping);
}
/**
* collapse_file - collapse filemap/tmpfs/shmem pages into huge one.
*
* 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;
struct mem_cgroup *memcg;
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);
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_try_charge(new_page, mm, gfp, &memcg, true))) {
result = SCAN_CGROUP_CHARGE_FAIL;
goto out;
}
/* 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)) {
mem_cgroup_cancel_charge(new_page, memcg, true);
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_NOHUGE)) {
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,
PAGE_SIZE);
/* 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 (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)) {
/*
* 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;
}
if (is_shmem)
__inc_node_page_state(new_page, NR_SHMEM_THPS);
else {
__inc_node_page_state(new_page, NR_FILE_THPS);
filemap_nr_thps_inc(mapping);
}
if (nr_none) {
struct zone *zone = page_zone(new_page);
__mod_node_page_state(zone->zone_pgdat, NR_FILE_PAGES, nr_none);
if (is_shmem)
__mod_node_page_state(zone->zone_pgdat,
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);
mem_cgroup_commit_charge(new_page, memcg, false, true);
if (is_shmem) {
set_page_dirty(new_page);
lru_cache_add_anon(new_page);
} else {
lru_cache_add_file(new_page);
}
count_memcg_events(memcg, THP_COLLAPSE_ALLOC, 1);
/*
* 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);
mem_cgroup_cancel_charge(new_page, memcg, true);
new_page->mapping = NULL;
}
unlock_page(new_page);
out:
VM_BUG_ON(!list_empty(&pagelist));
/* 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 int khugepaged_collapse_pte_mapped_thps(struct mm_slot *mm_slot)
{
return 0;
}
#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(!down_read_trylock(&mm->mmap_sem)))
goto breakouterloop_mmap_sem;
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);
up_read(&mm->mmap_sem);
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_sem so break loop */
goto breakouterloop_mmap_sem;
if (progress >= pages)
goto breakouterloop;
}
}
breakouterloop:
up_read(&mm->mmap_sem); /* exit_mmap will destroy ptes after this */
breakouterloop_mmap_sem:
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 = khugepaged_pages_to_scan;
bool wait = true;
barrier(); /* write khugepaged_pages_to_scan to local stack */
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)
{
static struct task_struct *khugepaged_thread __read_mostly;
static DEFINE_MUTEX(khugepaged_mutex);
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;
}