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linux/mm/khugepaged.c
Xin Hao 1661867027 mm: khugepaged: avoid pointless allocation for "struct mm_slot" 
In __khugepaged_enter(), if "mm->flags" with MMF_VM_HUGEPAGE bit is set,
the "mm_slot" will be released and return, so we can call mm_slot_alloc()
after test_and_set_bit().

Link: https://lkml.kernel.org/r/20230531095817.11012-1-xhao@linux.alibaba.com
Signed-off-by: Xin Hao <xhao@linux.alibaba.com>
Reviewed-by: Andrew Morton <akpm@linux-foudation.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
2023-06-09 16:25:51 -07:00

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// 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/page_table_check.h>
#include <linux/swapops.h>
#include <linux/shmem_fs.h>
#include <asm/tlb.h>
#include <asm/pgalloc.h>
#include "internal.h"
#include "mm_slot.h"
enum scan_result {
SCAN_FAIL,
SCAN_SUCCEED,
SCAN_PMD_NULL,
SCAN_PMD_NONE,
SCAN_PMD_MAPPED,
SCAN_EXCEED_NONE_PTE,
SCAN_EXCEED_SWAP_PTE,
SCAN_EXCEED_SHARED_PTE,
SCAN_PTE_NON_PRESENT,
SCAN_PTE_UFFD_WP,
SCAN_PTE_MAPPED_HUGEPAGE,
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_DEL_PAGE_LRU,
SCAN_ALLOC_HUGE_PAGE_FAIL,
SCAN_CGROUP_CHARGE_FAIL,
SCAN_TRUNCATED,
SCAN_PAGE_HAS_PRIVATE,
SCAN_STORE_FAILED,
SCAN_COPY_MC,
SCAN_PAGE_FILLED,
};
#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.
*
* Note that these are only respected if collapse was initiated by khugepaged.
*/
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 collapse_control {
bool is_khugepaged;
/* Num pages scanned per node */
u32 node_load[MAX_NUMNODES];
/* nodemask for allocation fallback */
nodemask_t alloc_nmask;
};
/**
* struct khugepaged_mm_slot - khugepaged information per mm that is being scanned
* @slot: hash lookup from mm to mm_slot
* @nr_pte_mapped_thp: number of pte mapped THP
* @pte_mapped_thp: address array corresponding pte mapped THP
*/
struct khugepaged_mm_slot {
struct mm_slot slot;
/* 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 khugepaged_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_RW(scan_sleep_millisecs);
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_RW(alloc_sleep_millisecs);
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_RW(pages_to_scan);
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 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 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_RW(defrag);
/*
* 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 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 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_RW(max_ptes_none);
static ssize_t 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 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_RW(max_ptes_swap);
static ssize_t 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 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_RW(max_ptes_shared);
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.
*/
khugepaged_enter_vma(vma, *vm_flags);
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 khugepaged_mm_slot),
__alignof__(struct khugepaged_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 int hpage_collapse_test_exit(struct mm_struct *mm)
{
return atomic_read(&mm->mm_users) == 0;
}
void __khugepaged_enter(struct mm_struct *mm)
{
struct khugepaged_mm_slot *mm_slot;
struct mm_slot *slot;
int wakeup;
/* __khugepaged_exit() must not run from under us */
VM_BUG_ON_MM(hpage_collapse_test_exit(mm), mm);
if (unlikely(test_and_set_bit(MMF_VM_HUGEPAGE, &mm->flags)))
return;
mm_slot = mm_slot_alloc(mm_slot_cache);
if (!mm_slot)
return;
slot = &mm_slot->slot;
spin_lock(&khugepaged_mm_lock);
mm_slot_insert(mm_slots_hash, 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(&slot->mm_node, &khugepaged_scan.mm_head);
spin_unlock(&khugepaged_mm_lock);
mmgrab(mm);
if (wakeup)
wake_up_interruptible(&khugepaged_wait);
}
void khugepaged_enter_vma(struct vm_area_struct *vma,
unsigned long vm_flags)
{
if (!test_bit(MMF_VM_HUGEPAGE, &vma->vm_mm->flags) &&
hugepage_flags_enabled()) {
if (hugepage_vma_check(vma, vm_flags, false, false, true))
__khugepaged_enter(vma->vm_mm);
}
}
void __khugepaged_exit(struct mm_struct *mm)
{
struct khugepaged_mm_slot *mm_slot;
struct mm_slot *slot;
int free = 0;
spin_lock(&khugepaged_mm_lock);
slot = mm_slot_lookup(mm_slots_hash, mm);
mm_slot = mm_slot_entry(slot, struct khugepaged_mm_slot, slot);
if (mm_slot && khugepaged_scan.mm_slot != mm_slot) {
hash_del(&slot->hash);
list_del(&slot->mm_node);
free = 1;
}
spin_unlock(&khugepaged_mm_lock);
if (free) {
clear_bit(MMF_VM_HUGEPAGE, &mm->flags);
mm_slot_free(mm_slot_cache, mm_slot);
mmdrop(mm);
} else if (mm_slot) {
/*
* This is required to serialize against
* hpage_collapse_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_folio(struct folio *folio)
{
node_stat_mod_folio(folio,
NR_ISOLATED_ANON + folio_is_file_lru(folio),
-folio_nr_pages(folio));
folio_unlock(folio);
folio_putback_lru(folio);
}
static void release_pte_page(struct page *page)
{
release_pte_folio(page_folio(page));
}
static void release_pte_pages(pte_t *pte, pte_t *_pte,
struct list_head *compound_pagelist)
{
struct folio *folio, *tmp;
while (--_pte >= pte) {
pte_t pteval = *_pte;
unsigned long pfn;
if (pte_none(pteval))
continue;
pfn = pte_pfn(pteval);
if (is_zero_pfn(pfn))
continue;
folio = pfn_folio(pfn);
if (folio_test_large(folio))
continue;
release_pte_folio(folio);
}
list_for_each_entry_safe(folio, tmp, compound_pagelist, lru) {
list_del(&folio->lru);
release_pte_folio(folio);
}
}
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 collapse_control *cc,
struct list_head *compound_pagelist)
{
struct page *page = NULL;
pte_t *_pte;
int none_or_zero = 0, shared = 0, result = SCAN_FAIL, 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)))) {
++none_or_zero;
if (!userfaultfd_armed(vma) &&
(!cc->is_khugepaged ||
none_or_zero <= khugepaged_max_ptes_none)) {
continue;
} else {
result = SCAN_EXCEED_NONE_PTE;
count_vm_event(THP_SCAN_EXCEED_NONE_PTE);
goto out;
}
}
if (!pte_present(pteval)) {
result = SCAN_PTE_NON_PRESENT;
goto out;
}
if (pte_uffd_wp(pteval)) {
result = SCAN_PTE_UFFD_WP;
goto out;
}
page = vm_normal_page(vma, address, pteval);
if (unlikely(!page) || unlikely(is_zone_device_page(page))) {
result = SCAN_PAGE_NULL;
goto out;
}
VM_BUG_ON_PAGE(!PageAnon(page), page);
if (page_mapcount(page) > 1) {
++shared;
if (cc->is_khugepaged &&
shared > khugepaged_max_ptes_shared) {
result = SCAN_EXCEED_SHARED_PTE;
count_vm_event(THP_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;
}
/*
* 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:
/*
* If collapse was initiated by khugepaged, check that there is
* enough young pte to justify collapsing the page
*/
if (cc->is_khugepaged &&
(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(cc->is_khugepaged && !referenced)) {
result = SCAN_LACK_REFERENCED_PAGE;
} else {
result = SCAN_SUCCEED;
trace_mm_collapse_huge_page_isolate(page, none_or_zero,
referenced, writable, result);
return result;
}
out:
release_pte_pages(pte, _pte, compound_pagelist);
trace_mm_collapse_huge_page_isolate(page, none_or_zero,
referenced, writable, result);
return result;
}
static void __collapse_huge_page_copy_succeeded(pte_t *pte,
struct vm_area_struct *vma,
unsigned long address,
spinlock_t *ptl,
struct list_head *compound_pagelist)
{
struct page *src_page;
struct page *tmp;
pte_t *_pte;
pte_t pteval;
for (_pte = pte; _pte < pte + HPAGE_PMD_NR;
_pte++, address += PAGE_SIZE) {
pteval = *_pte;
if (pte_none(pteval) || is_zero_pfn(pte_pfn(pteval))) {
add_mm_counter(vma->vm_mm, MM_ANONPAGES, 1);
if (is_zero_pfn(pte_pfn(pteval))) {
/*
* ptl mostly unnecessary.
*/
spin_lock(ptl);
ptep_clear(vma->vm_mm, address, _pte);
spin_unlock(ptl);
}
} else {
src_page = pte_page(pteval);
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);
ptep_clear(vma->vm_mm, address, _pte);
page_remove_rmap(src_page, vma, 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);
mod_node_page_state(page_pgdat(src_page),
NR_ISOLATED_ANON + page_is_file_lru(src_page),
-compound_nr(src_page));
unlock_page(src_page);
free_swap_cache(src_page);
putback_lru_page(src_page);
}
}
static void __collapse_huge_page_copy_failed(pte_t *pte,
pmd_t *pmd,
pmd_t orig_pmd,
struct vm_area_struct *vma,
struct list_head *compound_pagelist)
{
spinlock_t *pmd_ptl;
/*
* Re-establish the PMD to point to the original page table
* entry. Restoring PMD needs to be done prior to releasing
* pages. Since pages are still isolated and locked here,
* acquiring anon_vma_lock_write is unnecessary.
*/
pmd_ptl = pmd_lock(vma->vm_mm, pmd);
pmd_populate(vma->vm_mm, pmd, pmd_pgtable(orig_pmd));
spin_unlock(pmd_ptl);
/*
* Release both raw and compound pages isolated
* in __collapse_huge_page_isolate.
*/
release_pte_pages(pte, pte + HPAGE_PMD_NR, compound_pagelist);
}
/*
* __collapse_huge_page_copy - attempts to copy memory contents from raw
* pages to a hugepage. Cleans up the raw pages if copying succeeds;
* otherwise restores the original page table and releases isolated raw pages.
* Returns SCAN_SUCCEED if copying succeeds, otherwise returns SCAN_COPY_MC.
*
* @pte: starting of the PTEs to copy from
* @page: the new hugepage to copy contents to
* @pmd: pointer to the new hugepage's PMD
* @orig_pmd: the original raw pages' PMD
* @vma: the original raw pages' virtual memory area
* @address: starting address to copy
* @ptl: lock on raw pages' PTEs
* @compound_pagelist: list that stores compound pages
*/
static int __collapse_huge_page_copy(pte_t *pte,
struct page *page,
pmd_t *pmd,
pmd_t orig_pmd,
struct vm_area_struct *vma,
unsigned long address,
spinlock_t *ptl,
struct list_head *compound_pagelist)
{
struct page *src_page;
pte_t *_pte;
pte_t pteval;
unsigned long _address;
int result = SCAN_SUCCEED;
/*
* Copying pages' contents is subject to memory poison at any iteration.
*/
for (_pte = pte, _address = address; _pte < pte + HPAGE_PMD_NR;
_pte++, page++, _address += PAGE_SIZE) {
pteval = *_pte;
if (pte_none(pteval) || is_zero_pfn(pte_pfn(pteval))) {
clear_user_highpage(page, _address);
continue;
}
src_page = pte_page(pteval);
if (copy_mc_user_highpage(page, src_page, _address, vma) > 0) {
result = SCAN_COPY_MC;
break;
}
}
if (likely(result == SCAN_SUCCEED))
__collapse_huge_page_copy_succeeded(pte, vma, address, ptl,
compound_pagelist);
else
__collapse_huge_page_copy_failed(pte, pmd, orig_pmd, vma,
compound_pagelist);
return result;
}
static void khugepaged_alloc_sleep(void)
{
DEFINE_WAIT(wait);
add_wait_queue(&khugepaged_wait, &wait);
__set_current_state(TASK_INTERRUPTIBLE|TASK_FREEZABLE);
schedule_timeout(msecs_to_jiffies(khugepaged_alloc_sleep_millisecs));
remove_wait_queue(&khugepaged_wait, &wait);
}
struct collapse_control khugepaged_collapse_control = {
.is_khugepaged = true,
};
static bool hpage_collapse_scan_abort(int nid, struct collapse_control *cc)
{
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 (cc->node_load[nid])
return false;
for (i = 0; i < MAX_NUMNODES; i++) {
if (!cc->node_load[i])
continue;
if (node_distance(nid, i) > node_reclaim_distance)
return true;
}
return false;
}
#define khugepaged_defrag() \
(transparent_hugepage_flags & \
(1<<TRANSPARENT_HUGEPAGE_DEFRAG_KHUGEPAGED_FLAG))
/* 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 hpage_collapse_find_target_node(struct collapse_control *cc)
{
int nid, target_node = 0, max_value = 0;
/* find first node with max normal pages hit */
for (nid = 0; nid < MAX_NUMNODES; nid++)
if (cc->node_load[nid] > max_value) {
max_value = cc->node_load[nid];
target_node = nid;
}
for_each_online_node(nid) {
if (max_value == cc->node_load[nid])
node_set(nid, cc->alloc_nmask);
}
return target_node;
}
#else
static int hpage_collapse_find_target_node(struct collapse_control *cc)
{
return 0;
}
#endif
static bool hpage_collapse_alloc_page(struct page **hpage, gfp_t gfp, int node,
nodemask_t *nmask)
{
*hpage = __alloc_pages(gfp, HPAGE_PMD_ORDER, node, nmask);
if (unlikely(!*hpage)) {
count_vm_event(THP_COLLAPSE_ALLOC_FAILED);
return false;
}
prep_transhuge_page(*hpage);
count_vm_event(THP_COLLAPSE_ALLOC);
return true;
}
/*
* If mmap_lock temporarily dropped, revalidate vma
* before taking mmap_lock.
* Returns enum scan_result value.
*/
static int hugepage_vma_revalidate(struct mm_struct *mm, unsigned long address,
bool expect_anon,
struct vm_area_struct **vmap,
struct collapse_control *cc)
{
struct vm_area_struct *vma;
if (unlikely(hpage_collapse_test_exit(mm)))
return SCAN_ANY_PROCESS;
*vmap = vma = find_vma(mm, address);
if (!vma)
return SCAN_VMA_NULL;
if (!transhuge_vma_suitable(vma, address))
return SCAN_ADDRESS_RANGE;
if (!hugepage_vma_check(vma, vma->vm_flags, false, false,
cc->is_khugepaged))
return SCAN_VMA_CHECK;
/*
* Anon VMA expected, the address may be unmapped then
* remapped to file after khugepaged reaquired the mmap_lock.
*
* hugepage_vma_check may return true for qualified file
* vmas.
*/
if (expect_anon && (!(*vmap)->anon_vma || !vma_is_anonymous(*vmap)))
return SCAN_PAGE_ANON;
return SCAN_SUCCEED;
}
/*
* See pmd_trans_unstable() for how the result may change out from
* underneath us, even if we hold mmap_lock in read.
*/
static int find_pmd_or_thp_or_none(struct mm_struct *mm,
unsigned long address,
pmd_t **pmd)
{
pmd_t pmde;
*pmd = mm_find_pmd(mm, address);
if (!*pmd)
return SCAN_PMD_NULL;
pmde = pmdp_get_lockless(*pmd);
#ifdef CONFIG_TRANSPARENT_HUGEPAGE
/* See comments in pmd_none_or_trans_huge_or_clear_bad() */
barrier();
#endif
if (pmd_none(pmde))
return SCAN_PMD_NONE;
if (!pmd_present(pmde))
return SCAN_PMD_NULL;
if (pmd_trans_huge(pmde))
return SCAN_PMD_MAPPED;
if (pmd_devmap(pmde))
return SCAN_PMD_NULL;
if (pmd_bad(pmde))
return SCAN_PMD_NULL;
return SCAN_SUCCEED;
}
static int check_pmd_still_valid(struct mm_struct *mm,
unsigned long address,
pmd_t *pmd)
{
pmd_t *new_pmd;
int result = find_pmd_or_thp_or_none(mm, address, &new_pmd);
if (result != SCAN_SUCCEED)
return result;
if (new_pmd != pmd)
return SCAN_FAIL;
return SCAN_SUCCEED;
}
/*
* Bring missing pages in from swap, to complete THP collapse.
* Only done if hpage_collapse_scan_pmd believes it is worthwhile.
*
* Called and returns without pte mapped or spinlocks held.
* Note that if false is returned, mmap_lock will be released.
*/
static int __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;
}
ret = do_swap_page(&vmf);
/*
* do_swap_page returns VM_FAULT_RETRY with released mmap_lock.
* Note we treat VM_FAULT_RETRY as VM_FAULT_ERROR here because
* we do not retry here and swap entry will remain in pagetable
* resulting in later failure.
*/
if (ret & VM_FAULT_RETRY) {
trace_mm_collapse_huge_page_swapin(mm, swapped_in, referenced, 0);
/* Likely, but not guaranteed, that page lock failed */
return SCAN_PAGE_LOCK;
}
if (ret & VM_FAULT_ERROR) {
mmap_read_unlock(mm);
trace_mm_collapse_huge_page_swapin(mm, swapped_in, referenced, 0);
return SCAN_FAIL;
}
swapped_in++;
}
/* 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 SCAN_SUCCEED;
}
static int alloc_charge_hpage(struct page **hpage, struct mm_struct *mm,
struct collapse_control *cc)
{
gfp_t gfp = (cc->is_khugepaged ? alloc_hugepage_khugepaged_gfpmask() :
GFP_TRANSHUGE);
int node = hpage_collapse_find_target_node(cc);
struct folio *folio;
if (!hpage_collapse_alloc_page(hpage, gfp, node, &cc->alloc_nmask))
return SCAN_ALLOC_HUGE_PAGE_FAIL;
folio = page_folio(*hpage);
if (unlikely(mem_cgroup_charge(folio, mm, gfp))) {
folio_put(folio);
*hpage = NULL;
return SCAN_CGROUP_CHARGE_FAIL;
}
count_memcg_page_event(*hpage, THP_COLLAPSE_ALLOC);
return SCAN_SUCCEED;
}
static int collapse_huge_page(struct mm_struct *mm, unsigned long address,
int referenced, int unmapped,
struct collapse_control *cc)
{
LIST_HEAD(compound_pagelist);
pmd_t *pmd, _pmd;
pte_t *pte;
pgtable_t pgtable;
struct page *hpage;
spinlock_t *pmd_ptl, *pte_ptl;
int result = SCAN_FAIL;
struct vm_area_struct *vma;
struct mmu_notifier_range range;
VM_BUG_ON(address & ~HPAGE_PMD_MASK);
/*
* 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);
result = alloc_charge_hpage(&hpage, mm, cc);
if (result != SCAN_SUCCEED)
goto out_nolock;
mmap_read_lock(mm);
result = hugepage_vma_revalidate(mm, address, true, &vma, cc);
if (result != SCAN_SUCCEED) {
mmap_read_unlock(mm);
goto out_nolock;
}
result = find_pmd_or_thp_or_none(mm, address, &pmd);
if (result != SCAN_SUCCEED) {
mmap_read_unlock(mm);
goto out_nolock;
}
if (unmapped) {
/*
* __collapse_huge_page_swapin will return with mmap_lock
* released when it fails. So we jump out_nolock directly in
* that case. Continuing to collapse causes inconsistency.
*/
result = __collapse_huge_page_swapin(mm, vma, address, pmd,
referenced);
if (result != SCAN_SUCCEED)
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, true, &vma, cc);
if (result != SCAN_SUCCEED)
goto out_up_write;
/* check if the pmd is still valid */
result = check_pmd_still_valid(mm, address, pmd);
if (result != SCAN_SUCCEED)
goto out_up_write;
vma_start_write(vma);
anon_vma_lock_write(vma->anon_vma);
mmu_notifier_range_init(&range, MMU_NOTIFY_CLEAR, 0, 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 */
/*
* This 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.
*
* Parallel fast GUP is fine since fast GUP will back off when
* it detects PMD is changed.
*/
_pmd = pmdp_collapse_flush(vma, address, pmd);
spin_unlock(pmd_ptl);
mmu_notifier_invalidate_range_end(&range);
tlb_remove_table_sync_one();
spin_lock(pte_ptl);
result = __collapse_huge_page_isolate(vma, address, pte, cc,
&compound_pagelist);
spin_unlock(pte_ptl);
if (unlikely(result != SCAN_SUCCEED)) {
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);
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);
result = __collapse_huge_page_copy(pte, hpage, pmd, _pmd,
vma, address, pte_ptl,
&compound_pagelist);
pte_unmap(pte);
if (unlikely(result != SCAN_SUCCEED))
goto out_up_write;
/*
* 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(hpage);
pgtable = pmd_pgtable(_pmd);
_pmd = mk_huge_pmd(hpage, 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(hpage, vma, address);
lru_cache_add_inactive_or_unevictable(hpage, 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;
result = SCAN_SUCCEED;
out_up_write:
mmap_write_unlock(mm);
out_nolock:
if (hpage)
put_page(hpage);
trace_mm_collapse_huge_page(mm, result == SCAN_SUCCEED, result);
return result;
}
static int hpage_collapse_scan_pmd(struct mm_struct *mm,
struct vm_area_struct *vma,
unsigned long address, bool *mmap_locked,
struct collapse_control *cc)
{
pmd_t *pmd;
pte_t *pte, *_pte;
int result = SCAN_FAIL, referenced = 0;
int none_or_zero = 0, shared = 0;
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);
result = find_pmd_or_thp_or_none(mm, address, &pmd);
if (result != SCAN_SUCCEED)
goto out;
memset(cc->node_load, 0, sizeof(cc->node_load));
nodes_clear(cc->alloc_nmask);
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)) {
++unmapped;
if (!cc->is_khugepaged ||
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_any(pteval)) {
result = SCAN_PTE_UFFD_WP;
goto out_unmap;
}
continue;
} else {
result = SCAN_EXCEED_SWAP_PTE;
count_vm_event(THP_SCAN_EXCEED_SWAP_PTE);
goto out_unmap;
}
}
if (pte_none(pteval) || is_zero_pfn(pte_pfn(pteval))) {
++none_or_zero;
if (!userfaultfd_armed(vma) &&
(!cc->is_khugepaged ||
none_or_zero <= khugepaged_max_ptes_none)) {
continue;
} else {
result = SCAN_EXCEED_NONE_PTE;
count_vm_event(THP_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) || unlikely(is_zone_device_page(page))) {
result = SCAN_PAGE_NULL;
goto out_unmap;
}
if (page_mapcount(page) > 1) {
++shared;
if (cc->is_khugepaged &&
shared > khugepaged_max_ptes_shared) {
result = SCAN_EXCEED_SHARED_PTE;
count_vm_event(THP_SCAN_EXCEED_SHARED_PTE);
goto out_unmap;
}
}
page = compound_head(page);
/*
* Record which node the original page is from and save this
* information to cc->node_load[].
* Khugepaged will allocate hugepage from the node has the max
* hit record.
*/
node = page_to_nid(page);
if (hpage_collapse_scan_abort(node, cc)) {
result = SCAN_SCAN_ABORT;
goto out_unmap;
}
cc->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 may be racy:
* it may see total_mapcount > refcount in some cases?
* 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 collapse was initiated by khugepaged, check that there is
* enough young pte to justify collapsing the page
*/
if (cc->is_khugepaged &&
(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 (cc->is_khugepaged &&
(!referenced ||
(unmapped && referenced < HPAGE_PMD_NR / 2))) {
result = SCAN_LACK_REFERENCED_PAGE;
} else {
result = SCAN_SUCCEED;
}
out_unmap:
pte_unmap_unlock(pte, ptl);
if (result == SCAN_SUCCEED) {
result = collapse_huge_page(mm, address, referenced,
unmapped, cc);
/* collapse_huge_page will return with the mmap_lock released */
*mmap_locked = false;
}
out:
trace_mm_khugepaged_scan_pmd(mm, page, writable, referenced,
none_or_zero, result, unmapped);
return result;
}
static void collect_mm_slot(struct khugepaged_mm_slot *mm_slot)
{
struct mm_slot *slot = &mm_slot->slot;
struct mm_struct *mm = slot->mm;
lockdep_assert_held(&khugepaged_mm_lock);
if (hpage_collapse_test_exit(mm)) {
/* free mm_slot */
hash_del(&slot->hash);
list_del(&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 */
mm_slot_free(mm_slot_cache, 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.
*
* Note that following race exists:
* (1) khugepaged calls khugepaged_collapse_pte_mapped_thps() for mm_struct A,
* emptying the A's ->pte_mapped_thp[] array.
* (2) MADV_COLLAPSE collapses some file extent with target mm_struct B, and
* retract_page_tables() finds a VMA in mm_struct A mapping the same extent
* (at virtual address X) and adds an entry (for X) into mm_struct A's
* ->pte-mapped_thp[] array.
* (3) khugepaged calls khugepaged_collapse_scan_file() for mm_struct A at X,
* sees a pte-mapped THP (SCAN_PTE_MAPPED_HUGEPAGE) and adds an entry
* (for X) into mm_struct A's ->pte-mapped_thp[] array.
* Thus, it's possible the same address is added multiple times for the same
* mm_struct. Should this happen, we'll simply attempt
* collapse_pte_mapped_thp() multiple times for the same address, under the same
* exclusive mmap_lock, and assuming the first call is successful, subsequent
* attempts will return quickly (without grabbing any additional locks) when
* a huge pmd is found in find_pmd_or_thp_or_none(). Since this is a cheap
* check, and since this is a rare occurrence, the cost of preventing this
* "multiple-add" is thought to be more expensive than just handling it, should
* it occur.
*/
static bool khugepaged_add_pte_mapped_thp(struct mm_struct *mm,
unsigned long addr)
{
struct khugepaged_mm_slot *mm_slot;
struct mm_slot *slot;
bool ret = false;
VM_BUG_ON(addr & ~HPAGE_PMD_MASK);
spin_lock(&khugepaged_mm_lock);
slot = mm_slot_lookup(mm_slots_hash, mm);
mm_slot = mm_slot_entry(slot, struct khugepaged_mm_slot, slot);
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;
ret = true;
}
spin_unlock(&khugepaged_mm_lock);
return ret;
}
/* hpage must be locked, and mmap_lock must be held in write */
static int set_huge_pmd(struct vm_area_struct *vma, unsigned long addr,
pmd_t *pmdp, struct page *hpage)
{
struct vm_fault vmf = {
.vma = vma,
.address = addr,
.flags = 0,
.pmd = pmdp,
};
VM_BUG_ON(!PageTransHuge(hpage));
mmap_assert_write_locked(vma->vm_mm);
if (do_set_pmd(&vmf, hpage))
return SCAN_FAIL;
get_page(hpage);
return SCAN_SUCCEED;
}
/*
* A note about locking:
* Trying to take the page table spinlocks would be useless here because those
* are only used to synchronize:
*
* - modifying terminal entries (ones that point to a data page, not to another
* page table)
* - installing *new* non-terminal entries
*
* Instead, we need roughly the same kind of protection as free_pgtables() or
* mm_take_all_locks() (but only for a single VMA):
* The mmap lock together with this VMA's rmap locks covers all paths towards
* the page table entries we're messing with here, except for hardware page
* table walks and lockless_pages_from_mm().
*/
static void collapse_and_free_pmd(struct mm_struct *mm, struct vm_area_struct *vma,
unsigned long addr, pmd_t *pmdp)
{
pmd_t pmd;
struct mmu_notifier_range range;
mmap_assert_write_locked(mm);
if (vma->vm_file)
lockdep_assert_held_write(&vma->vm_file->f_mapping->i_mmap_rwsem);
/*
* All anon_vmas attached to the VMA have the same root and are
* therefore locked by the same lock.
*/
if (vma->anon_vma)
lockdep_assert_held_write(&vma->anon_vma->root->rwsem);
mmu_notifier_range_init(&range, MMU_NOTIFY_CLEAR, 0, mm, addr,
addr + HPAGE_PMD_SIZE);
mmu_notifier_invalidate_range_start(&range);
pmd = pmdp_collapse_flush(vma, addr, pmdp);
tlb_remove_table_sync_one();
mmu_notifier_invalidate_range_end(&range);
mm_dec_nr_ptes(mm);
page_table_check_pte_clear_range(mm, addr, pmd);
pte_free(mm, pmd_pgtable(pmd));
}
/**
* 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
* @install_pmd: If a huge PMD should be installed
*
* 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. Possibly install a huge PMD mapping the THP.
*/
int collapse_pte_mapped_thp(struct mm_struct *mm, unsigned long addr,
bool install_pmd)
{
unsigned long haddr = addr & HPAGE_PMD_MASK;
struct vm_area_struct *vma = vma_lookup(mm, haddr);
struct page *hpage;
pte_t *start_pte, *pte;
pmd_t *pmd;
spinlock_t *ptl;
int count = 0, result = SCAN_FAIL;
int i;
mmap_assert_write_locked(mm);
/* Fast check before locking page if already PMD-mapped */
result = find_pmd_or_thp_or_none(mm, haddr, &pmd);
if (result == SCAN_PMD_MAPPED)
return result;
if (!vma || !vma->vm_file ||
!range_in_vma(vma, haddr, haddr + HPAGE_PMD_SIZE))
return SCAN_VMA_CHECK;
/*
* If we are here, we've succeeded in replacing all the native pages
* in the page cache with a single hugepage. If a mm were to fault-in
* this memory (mapped by a suitably aligned VMA), we'd get the hugepage
* and map it by a PMD, regardless of sysfs THP settings. As such, let's
* analogously elide sysfs THP settings here.
*/
if (!hugepage_vma_check(vma, vma->vm_flags, false, false, false))
return SCAN_VMA_CHECK;
/* Keep pmd pgtable for uffd-wp; see comment in retract_page_tables() */
if (userfaultfd_wp(vma))
return SCAN_PTE_UFFD_WP;
hpage = find_lock_page(vma->vm_file->f_mapping,
linear_page_index(vma, haddr));
if (!hpage)
return SCAN_PAGE_NULL;
if (!PageHead(hpage)) {
result = SCAN_FAIL;
goto drop_hpage;
}
if (compound_order(hpage) != HPAGE_PMD_ORDER) {
result = SCAN_PAGE_COMPOUND;
goto drop_hpage;
}
switch (result) {
case SCAN_SUCCEED:
break;
case SCAN_PMD_NONE:
/*
* In MADV_COLLAPSE path, possible race with khugepaged where
* all pte entries have been removed and pmd cleared. If so,
* skip all the pte checks and just update the pmd mapping.
*/
goto maybe_install_pmd;
default:
goto drop_hpage;
}
/* Lock the vma before taking i_mmap and page table locks */
vma_start_write(vma);
/*
* We need to lock the mapping so that from here on, only GUP-fast and
* hardware page walks can access the parts of the page tables that
* we're operating on.
* See collapse_and_free_pmd().
*/
i_mmap_lock_write(vma->vm_file->f_mapping);
/*
* This spinlock should be unnecessary: Nobody else should be accessing
* the page tables under spinlock protection here, only
* lockless_pages_from_mm() and the hardware page walker can access page
* tables while all the high-level locks are held in write mode.
*/
start_pte = pte_offset_map_lock(mm, pmd, haddr, &ptl);
result = SCAN_FAIL;
/* 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)) {
result = SCAN_PTE_NON_PRESENT;
goto abort;
}
page = vm_normal_page(vma, addr, *pte);
if (WARN_ON_ONCE(page && is_zone_device_page(page)))
page = NULL;
/*
* 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);
if (WARN_ON_ONCE(page && is_zone_device_page(page)))
goto abort;
page_remove_rmap(page, vma, 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: remove pte entries */
/* we make no change to anon, but protect concurrent anon page lookup */
if (vma->anon_vma)
anon_vma_lock_write(vma->anon_vma);
collapse_and_free_pmd(mm, vma, haddr, pmd);
if (vma->anon_vma)
anon_vma_unlock_write(vma->anon_vma);
i_mmap_unlock_write(vma->vm_file->f_mapping);
maybe_install_pmd:
/* step 5: install pmd entry */
result = install_pmd
? set_huge_pmd(vma, haddr, pmd, hpage)
: SCAN_SUCCEED;
drop_hpage:
unlock_page(hpage);
put_page(hpage);
return result;
abort:
pte_unmap_unlock(start_pte, ptl);
i_mmap_unlock_write(vma->vm_file->f_mapping);
goto drop_hpage;
}
static void khugepaged_collapse_pte_mapped_thps(struct khugepaged_mm_slot *mm_slot)
{
struct mm_slot *slot = &mm_slot->slot;
struct mm_struct *mm = slot->mm;
int i;
if (likely(mm_slot->nr_pte_mapped_thp == 0))
return;
if (!mmap_write_trylock(mm))
return;
if (unlikely(hpage_collapse_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], false);
out:
mm_slot->nr_pte_mapped_thp = 0;
mmap_write_unlock(mm);
}
static int retract_page_tables(struct address_space *mapping, pgoff_t pgoff,
struct mm_struct *target_mm,
unsigned long target_addr, struct page *hpage,
struct collapse_control *cc)
{
struct vm_area_struct *vma;
int target_result = SCAN_FAIL;
i_mmap_lock_write(mapping);
vma_interval_tree_foreach(vma, &mapping->i_mmap, pgoff, pgoff) {
int result = SCAN_FAIL;
struct mm_struct *mm = NULL;
unsigned long addr = 0;
pmd_t *pmd;
bool is_target = false;
/*
* 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.
*
* Note 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. It would also probably require locking
* the anon_vma.
*/
if (READ_ONCE(vma->anon_vma)) {
result = SCAN_PAGE_ANON;
goto next;
}
addr = vma->vm_start + ((pgoff - vma->vm_pgoff) << PAGE_SHIFT);
if (addr & ~HPAGE_PMD_MASK ||
vma->vm_end < addr + HPAGE_PMD_SIZE) {
result = SCAN_VMA_CHECK;
goto next;
}
mm = vma->vm_mm;
is_target = mm == target_mm && addr == target_addr;
result = find_pmd_or_thp_or_none(mm, addr, &pmd);
if (result != SCAN_SUCCEED)
goto next;
/*
* 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.
*
* Also, it's not MADV_COLLAPSE's job to collapse other
* mappings - let khugepaged take care of them later.
*/
result = SCAN_PTE_MAPPED_HUGEPAGE;
if ((cc->is_khugepaged || is_target) &&
mmap_write_trylock(mm)) {
/* trylock for the same lock inversion as above */
if (!vma_try_start_write(vma))
goto unlock_next;
/*
* Re-check whether we have an ->anon_vma, because
* collapse_and_free_pmd() requires that either no
* ->anon_vma exists or the anon_vma is locked.
* We already checked ->anon_vma above, but that check
* is racy because ->anon_vma can be populated under the
* mmap lock in read mode.
*/
if (vma->anon_vma) {
result = SCAN_PAGE_ANON;
goto unlock_next;
}
/*
* When a vma is registered with uffd-wp, we can't
* recycle the pmd pgtable because there can be pte
* markers installed. Skip it only, so the rest mm/vma
* can still have the same file mapped hugely, however
* it'll always mapped in small page size for uffd-wp
* registered ranges.
*/
if (hpage_collapse_test_exit(mm)) {
result = SCAN_ANY_PROCESS;
goto unlock_next;
}
if (userfaultfd_wp(vma)) {
result = SCAN_PTE_UFFD_WP;
goto unlock_next;
}
collapse_and_free_pmd(mm, vma, addr, pmd);
if (!cc->is_khugepaged && is_target)
result = set_huge_pmd(vma, addr, pmd, hpage);
else
result = SCAN_SUCCEED;
unlock_next:
mmap_write_unlock(mm);
goto next;
}
/*
* Calling context will handle target mm/addr. Otherwise, let
* khugepaged try again later.
*/
if (!is_target) {
khugepaged_add_pte_mapped_thp(mm, addr);
continue;
}
next:
if (is_target)
target_result = result;
}
i_mmap_unlock_write(mapping);
return target_result;
}
/**
* collapse_file - collapse filemap/tmpfs/shmem pages into huge one.
*
* @mm: process address space where collapse happens
* @addr: virtual collapse start address
* @file: file that collapse on
* @start: collapse start address
* @cc: collapse context and scratchpad
*
* Basic scheme is simple, details are more complex:
* - allocate and lock a new huge page;
* - scan page cache, locking old pages
* + swap/gup in pages if necessary;
* - copy data to new page
* - handle shmem holes
* + re-validate that holes weren't filled by someone else
* + check for userfaultfd
* - finalize updates to the page cache;
* - if replacing succeeds:
* + unlock huge page;
* + free old pages;
* - if replacing failed;
* + unlock old pages
* + unlock and free huge page;
*/
static int collapse_file(struct mm_struct *mm, unsigned long addr,
struct file *file, pgoff_t start,
struct collapse_control *cc)
{
struct address_space *mapping = file->f_mapping;
struct page *hpage;
struct page *page;
struct page *tmp;
struct folio *folio;
pgoff_t index = 0, end = start + HPAGE_PMD_NR;
LIST_HEAD(pagelist);
XA_STATE_ORDER(xas, &mapping->i_pages, start, HPAGE_PMD_ORDER);
int nr_none = 0, result = SCAN_SUCCEED;
bool is_shmem = shmem_file(file);
int nr = 0;
VM_BUG_ON(!IS_ENABLED(CONFIG_READ_ONLY_THP_FOR_FS) && !is_shmem);
VM_BUG_ON(start & (HPAGE_PMD_NR - 1));
result = alloc_charge_hpage(&hpage, mm, cc);
if (result != SCAN_SUCCEED)
goto out;
__SetPageLocked(hpage);
if (is_shmem)
__SetPageSwapBacked(hpage);
hpage->index = start;
hpage->mapping = mapping;
/*
* Ensure we have slots for all the pages in the range. This is
* almost certainly a no-op because most of the pages must be present
*/
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 rollback;
}
} while (1);
xas_set(&xas, start);
for (index = start; index < end; index++) {
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 + 1);
}
if (!shmem_charge(mapping->host, 1)) {
result = SCAN_FAIL;
goto xa_locked;
}
nr_none++;
continue;
}
if (xa_is_value(page) || !PageUptodate(page)) {
xas_unlock_irq(&xas);
/* swap in or instantiate fallocated page */
if (shmem_get_folio(mapping->host, index,
&folio, SGP_NOALLOC)) {
result = SCAN_FAIL;
goto xa_unlocked;
}
/* drain pagevecs to help isolate_lru_page() */
lru_add_drain();
page = folio_file_page(folio, index);
} 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.
* This will be discovered on the first iteration.
*/
if (PageTransCompound(page)) {
struct page *head = compound_head(page);
result = compound_order(head) == HPAGE_PMD_ORDER &&
head->index == start
/* Maybe PMD-mapped */
? SCAN_PTE_MAPPED_HUGEPAGE
: SCAN_PAGE_COMPOUND;
goto out_unlock;
}
folio = page_folio(page);
if (folio_mapping(folio) != mapping) {
result = SCAN_TRUNCATED;
goto out_unlock;
}
if (!is_shmem && (folio_test_dirty(folio) ||
folio_test_writeback(folio))) {
/*
* 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 (!folio_isolate_lru(folio)) {
result = SCAN_DEL_PAGE_LRU;
goto out_unlock;
}
if (folio_has_private(folio) &&
!filemap_release_folio(folio, GFP_KERNEL)) {
result = SCAN_PAGE_HAS_PRIVATE;
folio_putback_lru(folio);
goto out_unlock;
}
if (folio_mapped(folio))
try_to_unmap(folio,
TTU_IGNORE_MLOCK | TTU_BATCH_FLUSH);
xas_lock_irq(&xas);
xas_set(&xas, index);
VM_BUG_ON_PAGE(page != xas_load(&xas), page);
/*
* We control three references to the page:
* - we hold a pin on it;
* - one reference from page cache;
* - one from isolate_lru_page;
* If those are the only references, then any new usage of the
* page will have to fetch it from the page cache. That requires
* locking the page to handle truncate, so any new usage will be
* blocked until we unlock page after collapse/during rollback.
*/
if (page_count(page) != 3) {
result = SCAN_PAGE_COUNT;
xas_unlock_irq(&xas);
putback_lru_page(page);
goto out_unlock;
}
/*
* Accumulate the pages that are being collapsed.
*/
list_add_tail(&page->lru, &pagelist);
continue;
out_unlock:
unlock_page(page);
put_page(page);
goto xa_unlocked;
}
if (!is_shmem) {
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;
filemap_nr_thps_dec(mapping);
}
}
xa_locked:
xas_unlock_irq(&xas);
xa_unlocked:
/*
* If collapse is successful, flush must be done now before copying.
* If collapse is unsuccessful, does flush actually need to be done?
* Do it anyway, to clear the state.
*/
try_to_unmap_flush();
if (result != SCAN_SUCCEED)
goto rollback;
/*
* The old pages are locked, so they won't change anymore.
*/
index = start;
list_for_each_entry(page, &pagelist, lru) {
while (index < page->index) {
clear_highpage(hpage + (index % HPAGE_PMD_NR));
index++;
}
if (copy_mc_highpage(hpage + (page->index % HPAGE_PMD_NR), page) > 0) {
result = SCAN_COPY_MC;
goto rollback;
}
index++;
}
while (index < end) {
clear_highpage(hpage + (index % HPAGE_PMD_NR));
index++;
}
if (nr_none) {
struct vm_area_struct *vma;
int nr_none_check = 0;
i_mmap_lock_read(mapping);
xas_lock_irq(&xas);
xas_set(&xas, start);
for (index = start; index < end; index++) {
if (!xas_next(&xas)) {
xas_store(&xas, XA_RETRY_ENTRY);
if (xas_error(&xas)) {
result = SCAN_STORE_FAILED;
goto immap_locked;
}
nr_none_check++;
}
}
if (nr_none != nr_none_check) {
result = SCAN_PAGE_FILLED;
goto immap_locked;
}
/*
* If userspace observed a missing page in a VMA with a MODE_MISSING
* userfaultfd, then it might expect a UFFD_EVENT_PAGEFAULT for that
* page. If so, we need to roll back to avoid suppressing such an
* event. Since wp/minor userfaultfds don't give userspace any
* guarantees that the kernel doesn't fill a missing page with a zero
* page, so they don't matter here.
*
* Any userfaultfds registered after this point will not be able to
* observe any missing pages due to the previously inserted retry
* entries.
*/
vma_interval_tree_foreach(vma, &mapping->i_mmap, start, end) {
if (userfaultfd_missing(vma)) {
result = SCAN_EXCEED_NONE_PTE;
goto immap_locked;
}
}
immap_locked:
i_mmap_unlock_read(mapping);
if (result != SCAN_SUCCEED) {
xas_set(&xas, start);
for (index = start; index < end; index++) {
if (xas_next(&xas) == XA_RETRY_ENTRY)
xas_store(&xas, NULL);
}
xas_unlock_irq(&xas);
goto rollback;
}
} else {
xas_lock_irq(&xas);
}
nr = thp_nr_pages(hpage);
if (is_shmem)
__mod_lruvec_page_state(hpage, NR_SHMEM_THPS, nr);
else
__mod_lruvec_page_state(hpage, NR_FILE_THPS, nr);
if (nr_none) {
__mod_lruvec_page_state(hpage, NR_FILE_PAGES, nr_none);
/* nr_none is always 0 for non-shmem. */
__mod_lruvec_page_state(hpage, NR_SHMEM, nr_none);
}
/*
* Mark hpage as uptodate before inserting it into the page cache so
* that it isn't mistaken for an fallocated but unwritten page.
*/
folio = page_folio(hpage);
folio_mark_uptodate(folio);
folio_ref_add(folio, HPAGE_PMD_NR - 1);
if (is_shmem)
folio_mark_dirty(folio);
folio_add_lru(folio);
/* Join all the small entries into a single multi-index entry. */
xas_set_order(&xas, start, HPAGE_PMD_ORDER);
xas_store(&xas, hpage);
WARN_ON_ONCE(xas_error(&xas));
xas_unlock_irq(&xas);
/*
* Remove pte page tables, so we can re-fault the page as huge.
*/
result = retract_page_tables(mapping, start, mm, addr, hpage,
cc);
unlock_page(hpage);
/*
* The collapse has succeeded, so free the old pages.
*/
list_for_each_entry_safe(page, tmp, &pagelist, lru) {
list_del(&page->lru);
page->mapping = NULL;
ClearPageActive(page);
ClearPageUnevictable(page);
unlock_page(page);
folio_put_refs(page_folio(page), 3);
}
goto out;
rollback:
/* Something went wrong: roll back page cache changes */
if (nr_none) {
xas_lock_irq(&xas);
mapping->nrpages -= nr_none;
shmem_uncharge(mapping->host, nr_none);
xas_unlock_irq(&xas);
}
list_for_each_entry_safe(page, tmp, &pagelist, lru) {
list_del(&page->lru);
unlock_page(page);
putback_lru_page(page);
put_page(page);
}
/*
* Undo the updates of filemap_nr_thps_inc for non-SHMEM
* file only. This undo is not needed unless failure is
* due to SCAN_COPY_MC.
*/
if (!is_shmem && result == SCAN_COPY_MC) {
filemap_nr_thps_dec(mapping);
/*
* Paired with smp_mb() in do_dentry_open() to
* ensure the update to nr_thps is visible.
*/
smp_mb();
}
hpage->mapping = NULL;
unlock_page(hpage);
put_page(hpage);
out:
VM_BUG_ON(!list_empty(&pagelist));
trace_mm_khugepaged_collapse_file(mm, hpage, index, is_shmem, addr, file, nr, result);
return result;
}
static int hpage_collapse_scan_file(struct mm_struct *mm, unsigned long addr,
struct file *file, pgoff_t start,
struct collapse_control *cc)
{
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(cc->node_load, 0, sizeof(cc->node_load));
nodes_clear(cc->alloc_nmask);
rcu_read_lock();
xas_for_each(&xas, page, start + HPAGE_PMD_NR - 1) {
if (xas_retry(&xas, page))
continue;
if (xa_is_value(page)) {
++swap;
if (cc->is_khugepaged &&
swap > khugepaged_max_ptes_swap) {
result = SCAN_EXCEED_SWAP_PTE;
count_vm_event(THP_SCAN_EXCEED_SWAP_PTE);
break;
}
continue;
}
/*
* TODO: khugepaged should compact smaller compound pages
* into a PMD sized page
*/
if (PageTransCompound(page)) {
struct page *head = compound_head(page);
result = compound_order(head) == HPAGE_PMD_ORDER &&
head->index == start
/* Maybe PMD-mapped */
? SCAN_PTE_MAPPED_HUGEPAGE
: SCAN_PAGE_COMPOUND;
/*
* For SCAN_PTE_MAPPED_HUGEPAGE, further processing
* by the caller won't touch the page cache, and so
* it's safe to skip LRU and refcount checks before
* returning.
*/
break;
}
node = page_to_nid(page);
if (hpage_collapse_scan_abort(node, cc)) {
result = SCAN_SCAN_ABORT;
break;
}
cc->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 (cc->is_khugepaged &&
present < HPAGE_PMD_NR - khugepaged_max_ptes_none) {
result = SCAN_EXCEED_NONE_PTE;
count_vm_event(THP_SCAN_EXCEED_NONE_PTE);
} else {
result = collapse_file(mm, addr, file, start, cc);
}
}
trace_mm_khugepaged_scan_file(mm, page, file, present, swap, result);
return result;
}
#else
static int hpage_collapse_scan_file(struct mm_struct *mm, unsigned long addr,
struct file *file, pgoff_t start,
struct collapse_control *cc)
{
BUILD_BUG();
}
static void khugepaged_collapse_pte_mapped_thps(struct khugepaged_mm_slot *mm_slot)
{
}
static bool khugepaged_add_pte_mapped_thp(struct mm_struct *mm,
unsigned long addr)
{
return false;
}
#endif
static unsigned int khugepaged_scan_mm_slot(unsigned int pages, int *result,
struct collapse_control *cc)
__releases(&khugepaged_mm_lock)
__acquires(&khugepaged_mm_lock)
{
struct vma_iterator vmi;
struct khugepaged_mm_slot *mm_slot;
struct mm_slot *slot;
struct mm_struct *mm;
struct vm_area_struct *vma;
int progress = 0;
VM_BUG_ON(!pages);
lockdep_assert_held(&khugepaged_mm_lock);
*result = SCAN_FAIL;
if (khugepaged_scan.mm_slot) {
mm_slot = khugepaged_scan.mm_slot;
slot = &mm_slot->slot;
} else {
slot = list_entry(khugepaged_scan.mm_head.next,
struct mm_slot, mm_node);
mm_slot = mm_slot_entry(slot, struct khugepaged_mm_slot, slot);
khugepaged_scan.address = 0;
khugepaged_scan.mm_slot = mm_slot;
}
spin_unlock(&khugepaged_mm_lock);
khugepaged_collapse_pte_mapped_thps(mm_slot);
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;
progress++;
if (unlikely(hpage_collapse_test_exit(mm)))
goto breakouterloop;
vma_iter_init(&vmi, mm, khugepaged_scan.address);
for_each_vma(vmi, vma) {
unsigned long hstart, hend;
cond_resched();
if (unlikely(hpage_collapse_test_exit(mm))) {
progress++;
break;
}
if (!hugepage_vma_check(vma, vma->vm_flags, false, false, true)) {
skip:
progress++;
continue;
}
hstart = round_up(vma->vm_start, HPAGE_PMD_SIZE);
hend = round_down(vma->vm_end, HPAGE_PMD_SIZE);
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);
while (khugepaged_scan.address < hend) {
bool mmap_locked = true;
cond_resched();
if (unlikely(hpage_collapse_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);
*result = hpage_collapse_scan_file(mm,
khugepaged_scan.address,
file, pgoff, cc);
mmap_locked = false;
fput(file);
} else {
*result = hpage_collapse_scan_pmd(mm, vma,
khugepaged_scan.address,
&mmap_locked,
cc);
}
switch (*result) {
case SCAN_PTE_MAPPED_HUGEPAGE: {
pmd_t *pmd;
*result = find_pmd_or_thp_or_none(mm,
khugepaged_scan.address,
&pmd);
if (*result != SCAN_SUCCEED)
break;
if (!khugepaged_add_pte_mapped_thp(mm,
khugepaged_scan.address))
break;
} fallthrough;
case SCAN_SUCCEED:
++khugepaged_pages_collapsed;
break;
default:
break;
}
/* move to next address */
khugepaged_scan.address += HPAGE_PMD_SIZE;
progress += HPAGE_PMD_NR;
if (!mmap_locked)
/*
* We released mmap_lock so break loop. Note
* that we drop mmap_lock before all hugepage
* allocations, so if allocation fails, we are
* guaranteed to break here and report the
* correct result back to caller.
*/
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 (hpage_collapse_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 (slot->mm_node.next != &khugepaged_scan.mm_head) {
slot = list_entry(slot->mm_node.next,
struct mm_slot, mm_node);
khugepaged_scan.mm_slot =
mm_slot_entry(slot, struct khugepaged_mm_slot, slot);
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) &&
hugepage_flags_enabled();
}
static int khugepaged_wait_event(void)
{
return !list_empty(&khugepaged_scan.mm_head) ||
kthread_should_stop();
}
static void khugepaged_do_scan(struct collapse_control *cc)
{
unsigned int progress = 0, pass_through_head = 0;
unsigned int pages = READ_ONCE(khugepaged_pages_to_scan);
bool wait = true;
int result = SCAN_SUCCEED;
lru_add_drain_all();
while (true) {
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,
&result, cc);
else
progress = pages;
spin_unlock(&khugepaged_mm_lock);
if (progress >= pages)
break;
if (result == SCAN_ALLOC_HUGE_PAGE_FAIL) {
/*
* If fail to allocate the first time, try to sleep for
* a while. When hit again, cancel the scan.
*/
if (!wait)
break;
wait = false;
khugepaged_alloc_sleep();
}
}
}
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 (hugepage_flags_enabled())
wait_event_freezable(khugepaged_wait, khugepaged_wait_event());
}
static int khugepaged(void *none)
{
struct khugepaged_mm_slot *mm_slot;
set_freezable();
set_user_nice(current, MAX_NICE);
while (!kthread_should_stop()) {
khugepaged_do_scan(&khugepaged_collapse_control);
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;
if (!hugepage_flags_enabled()) {
calculate_min_free_kbytes();
goto update_wmarks;
}
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;
}
update_wmarks:
setup_per_zone_wmarks();
}
int start_stop_khugepaged(void)
{
int err = 0;
mutex_lock(&khugepaged_mutex);
if (hugepage_flags_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);
} else if (khugepaged_thread) {
kthread_stop(khugepaged_thread);
khugepaged_thread = NULL;
}
set_recommended_min_free_kbytes();
fail:
mutex_unlock(&khugepaged_mutex);
return err;
}
void khugepaged_min_free_kbytes_update(void)
{
mutex_lock(&khugepaged_mutex);
if (hugepage_flags_enabled() && khugepaged_thread)
set_recommended_min_free_kbytes();
mutex_unlock(&khugepaged_mutex);
}
bool current_is_khugepaged(void)
{
return kthread_func(current) == khugepaged;
}
static int madvise_collapse_errno(enum scan_result r)
{
/*
* MADV_COLLAPSE breaks from existing madvise(2) conventions to provide
* actionable feedback to caller, so they may take an appropriate
* fallback measure depending on the nature of the failure.
*/
switch (r) {
case SCAN_ALLOC_HUGE_PAGE_FAIL:
return -ENOMEM;
case SCAN_CGROUP_CHARGE_FAIL:
case SCAN_EXCEED_NONE_PTE:
return -EBUSY;
/* Resource temporary unavailable - trying again might succeed */
case SCAN_PAGE_COUNT:
case SCAN_PAGE_LOCK:
case SCAN_PAGE_LRU:
case SCAN_DEL_PAGE_LRU:
case SCAN_PAGE_FILLED:
return -EAGAIN;
/*
* Other: Trying again likely not to succeed / error intrinsic to
* specified memory range. khugepaged likely won't be able to collapse
* either.
*/
default:
return -EINVAL;
}
}
int madvise_collapse(struct vm_area_struct *vma, struct vm_area_struct **prev,
unsigned long start, unsigned long end)
{
struct collapse_control *cc;
struct mm_struct *mm = vma->vm_mm;
unsigned long hstart, hend, addr;
int thps = 0, last_fail = SCAN_FAIL;
bool mmap_locked = true;
BUG_ON(vma->vm_start > start);
BUG_ON(vma->vm_end < end);
*prev = vma;
if (!hugepage_vma_check(vma, vma->vm_flags, false, false, false))
return -EINVAL;
cc = kmalloc(sizeof(*cc), GFP_KERNEL);
if (!cc)
return -ENOMEM;
cc->is_khugepaged = false;
mmgrab(mm);
lru_add_drain_all();
hstart = (start + ~HPAGE_PMD_MASK) & HPAGE_PMD_MASK;
hend = end & HPAGE_PMD_MASK;
for (addr = hstart; addr < hend; addr += HPAGE_PMD_SIZE) {
int result = SCAN_FAIL;
if (!mmap_locked) {
cond_resched();
mmap_read_lock(mm);
mmap_locked = true;
result = hugepage_vma_revalidate(mm, addr, false, &vma,
cc);
if (result != SCAN_SUCCEED) {
last_fail = result;
goto out_nolock;
}
hend = min(hend, vma->vm_end & HPAGE_PMD_MASK);
}
mmap_assert_locked(mm);
memset(cc->node_load, 0, sizeof(cc->node_load));
nodes_clear(cc->alloc_nmask);
if (IS_ENABLED(CONFIG_SHMEM) && vma->vm_file) {
struct file *file = get_file(vma->vm_file);
pgoff_t pgoff = linear_page_index(vma, addr);
mmap_read_unlock(mm);
mmap_locked = false;
result = hpage_collapse_scan_file(mm, addr, file, pgoff,
cc);
fput(file);
} else {
result = hpage_collapse_scan_pmd(mm, vma, addr,
&mmap_locked, cc);
}
if (!mmap_locked)
*prev = NULL; /* Tell caller we dropped mmap_lock */
handle_result:
switch (result) {
case SCAN_SUCCEED:
case SCAN_PMD_MAPPED:
++thps;
break;
case SCAN_PTE_MAPPED_HUGEPAGE:
BUG_ON(mmap_locked);
BUG_ON(*prev);
mmap_write_lock(mm);
result = collapse_pte_mapped_thp(mm, addr, true);
mmap_write_unlock(mm);
goto handle_result;
/* Whitelisted set of results where continuing OK */
case SCAN_PMD_NULL:
case SCAN_PTE_NON_PRESENT:
case SCAN_PTE_UFFD_WP:
case SCAN_PAGE_RO:
case SCAN_LACK_REFERENCED_PAGE:
case SCAN_PAGE_NULL:
case SCAN_PAGE_COUNT:
case SCAN_PAGE_LOCK:
case SCAN_PAGE_COMPOUND:
case SCAN_PAGE_LRU:
case SCAN_DEL_PAGE_LRU:
last_fail = result;
break;
default:
last_fail = result;
/* Other error, exit */
goto out_maybelock;
}
}
out_maybelock:
/* Caller expects us to hold mmap_lock on return */
if (!mmap_locked)
mmap_read_lock(mm);
out_nolock:
mmap_assert_locked(mm);
mmdrop(mm);
kfree(cc);
return thps == ((hend - hstart) >> HPAGE_PMD_SHIFT) ? 0
: madvise_collapse_errno(last_fail);
}
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