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migrate.c
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/*
* Memory Migration functionality - linux/mm/migrate.c
*
* Copyright (C) 2006 Silicon Graphics, Inc., Christoph Lameter
*
* Page migration was first developed in the context of the memory hotplug
* project. The main authors of the migration code are:
*
* IWAMOTO Toshihiro <[email protected]>
* Hirokazu Takahashi <[email protected]>
* Dave Hansen <[email protected]>
* Christoph Lameter
*/
#include <linux/migrate.h>
#include <linux/export.h>
#include <linux/swap.h>
#include <linux/swapops.h>
#include <linux/pagemap.h>
#include <linux/buffer_head.h>
#include <linux/mm_inline.h>
#include <linux/nsproxy.h>
#include <linux/pagevec.h>
#include <linux/ksm.h>
#include <linux/rmap.h>
#include <linux/topology.h>
#include <linux/cpu.h>
#include <linux/cpuset.h>
#include <linux/writeback.h>
#include <linux/mempolicy.h>
#include <linux/vmalloc.h>
#include <linux/security.h>
#include <linux/backing-dev.h>
#include <linux/compaction.h>
#include <linux/syscalls.h>
#include <linux/hugetlb.h>
#include <linux/hugetlb_cgroup.h>
#include <linux/gfp.h>
#include <linux/balloon_compaction.h>
#include <linux/mmu_notifier.h>
#include <linux/page_idle.h>
#include <linux/page_owner.h>
#include <linux/sched/mm.h>
#include <asm/tlbflush.h>
#define CREATE_TRACE_POINTS
#include <trace/events/migrate.h>
#include "internal.h"
/*
* migrate_prep() needs to be called before we start compiling a list of pages
* to be migrated using isolate_lru_page(). If scheduling work on other CPUs is
* undesirable, use migrate_prep_local()
*/
int migrate_prep(void)
{
/*
* Clear the LRU lists so pages can be isolated.
* Note that pages may be moved off the LRU after we have
* drained them. Those pages will fail to migrate like other
* pages that may be busy.
*/
lru_add_drain_all();
return 0;
}
/* Do the necessary work of migrate_prep but not if it involves other CPUs */
int migrate_prep_local(void)
{
lru_add_drain();
return 0;
}
int isolate_movable_page(struct page *page, isolate_mode_t mode)
{
struct address_space *mapping;
/*
* Avoid burning cycles with pages that are yet under __free_pages(),
* or just got freed under us.
*
* In case we 'win' a race for a movable page being freed under us and
* raise its refcount preventing __free_pages() from doing its job
* the put_page() at the end of this block will take care of
* release this page, thus avoiding a nasty leakage.
*/
if (unlikely(!get_page_unless_zero(page)))
goto out;
/*
* Check PageMovable before holding a PG_lock because page's owner
* assumes anybody doesn't touch PG_lock of newly allocated page
* so unconditionally grapping the lock ruins page's owner side.
*/
if (unlikely(!__PageMovable(page)))
goto out_putpage;
/*
* As movable pages are not isolated from LRU lists, concurrent
* compaction threads can race against page migration functions
* as well as race against the releasing a page.
*
* In order to avoid having an already isolated movable page
* being (wrongly) re-isolated while it is under migration,
* or to avoid attempting to isolate pages being released,
* lets be sure we have the page lock
* before proceeding with the movable page isolation steps.
*/
if (unlikely(!trylock_page(page)))
goto out_putpage;
if (!PageMovable(page) || PageIsolated(page))
goto out_no_isolated;
mapping = page_mapping(page);
VM_BUG_ON_PAGE(!mapping, page);
if (!mapping->a_ops->isolate_page(page, mode))
goto out_no_isolated;
/* Driver shouldn't use PG_isolated bit of page->flags */
WARN_ON_ONCE(PageIsolated(page));
__SetPageIsolated(page);
unlock_page(page);
return 0;
out_no_isolated:
unlock_page(page);
out_putpage:
put_page(page);
out:
return -EBUSY;
}
/* It should be called on page which is PG_movable */
void putback_movable_page(struct page *page)
{
struct address_space *mapping;
VM_BUG_ON_PAGE(!PageLocked(page), page);
VM_BUG_ON_PAGE(!PageMovable(page), page);
VM_BUG_ON_PAGE(!PageIsolated(page), page);
mapping = page_mapping(page);
mapping->a_ops->putback_page(page);
__ClearPageIsolated(page);
}
/*
* Put previously isolated pages back onto the appropriate lists
* from where they were once taken off for compaction/migration.
*
* This function shall be used whenever the isolated pageset has been
* built from lru, balloon, hugetlbfs page. See isolate_migratepages_range()
* and isolate_huge_page().
*/
void putback_movable_pages(struct list_head *l)
{
struct page *page;
struct page *page2;
list_for_each_entry_safe(page, page2, l, lru) {
if (unlikely(PageHuge(page))) {
putback_active_hugepage(page);
continue;
}
list_del(&page->lru);
/*
* We isolated non-lru movable page so here we can use
* __PageMovable because LRU page's mapping cannot have
* PAGE_MAPPING_MOVABLE.
*/
if (unlikely(__PageMovable(page))) {
VM_BUG_ON_PAGE(!PageIsolated(page), page);
lock_page(page);
if (PageMovable(page))
putback_movable_page(page);
else
__ClearPageIsolated(page);
unlock_page(page);
put_page(page);
} else {
dec_node_page_state(page, NR_ISOLATED_ANON +
page_is_file_cache(page));
putback_lru_page(page);
}
}
}
/*
* Restore a potential migration pte to a working pte entry
*/
static bool remove_migration_pte(struct page *page, struct vm_area_struct *vma,
unsigned long addr, void *old)
{
struct page_vma_mapped_walk pvmw = {
.page = old,
.vma = vma,
.address = addr,
.flags = PVMW_SYNC | PVMW_MIGRATION,
};
struct page *new;
pte_t pte;
swp_entry_t entry;
VM_BUG_ON_PAGE(PageTail(page), page);
while (page_vma_mapped_walk(&pvmw)) {
if (PageKsm(page))
new = page;
else
new = page - pvmw.page->index +
linear_page_index(vma, pvmw.address);
get_page(new);
pte = pte_mkold(mk_pte(new, READ_ONCE(vma->vm_page_prot)));
if (pte_swp_soft_dirty(*pvmw.pte))
pte = pte_mksoft_dirty(pte);
/*
* Recheck VMA as permissions can change since migration started
*/
entry = pte_to_swp_entry(*pvmw.pte);
if (is_write_migration_entry(entry))
pte = maybe_mkwrite(pte, vma);
flush_dcache_page(new);
#ifdef CONFIG_HUGETLB_PAGE
if (PageHuge(new)) {
pte = pte_mkhuge(pte);
pte = arch_make_huge_pte(pte, vma, new, 0);
set_huge_pte_at(vma->vm_mm, pvmw.address, pvmw.pte, pte);
if (PageAnon(new))
hugepage_add_anon_rmap(new, vma, pvmw.address);
else
page_dup_rmap(new, true);
} else
#endif
{
set_pte_at(vma->vm_mm, pvmw.address, pvmw.pte, pte);
if (PageAnon(new))
page_add_anon_rmap(new, vma, pvmw.address, false);
else
page_add_file_rmap(new, false);
}
if (vma->vm_flags & VM_LOCKED && !PageTransCompound(new))
mlock_vma_page(new);
/* No need to invalidate - it was non-present before */
update_mmu_cache(vma, pvmw.address, pvmw.pte);
}
return true;
}
/*
* Get rid of all migration entries and replace them by
* references to the indicated page.
*/
void remove_migration_ptes(struct page *old, struct page *new, bool locked)
{
struct rmap_walk_control rwc = {
.rmap_one = remove_migration_pte,
.arg = old,
};
if (locked)
rmap_walk_locked(new, &rwc);
else
rmap_walk(new, &rwc);
}
/*
* Something used the pte of a page under migration. We need to
* get to the page and wait until migration is finished.
* When we return from this function the fault will be retried.
*/
void __migration_entry_wait(struct mm_struct *mm, pte_t *ptep,
spinlock_t *ptl)
{
pte_t pte;
swp_entry_t entry;
struct page *page;
spin_lock(ptl);
pte = *ptep;
if (!is_swap_pte(pte))
goto out;
entry = pte_to_swp_entry(pte);
if (!is_migration_entry(entry))
goto out;
page = migration_entry_to_page(entry);
/*
* Once radix-tree replacement of page migration started, page_count
* *must* be zero. And, we don't want to call wait_on_page_locked()
* against a page without get_page().
* So, we use get_page_unless_zero(), here. Even failed, page fault
* will occur again.
*/
if (!get_page_unless_zero(page))
goto out;
pte_unmap_unlock(ptep, ptl);
wait_on_page_locked(page);
put_page(page);
return;
out:
pte_unmap_unlock(ptep, ptl);
}
void migration_entry_wait(struct mm_struct *mm, pmd_t *pmd,
unsigned long address)
{
spinlock_t *ptl = pte_lockptr(mm, pmd);
pte_t *ptep = pte_offset_map(pmd, address);
__migration_entry_wait(mm, ptep, ptl);
}
void migration_entry_wait_huge(struct vm_area_struct *vma,
struct mm_struct *mm, pte_t *pte)
{
spinlock_t *ptl = huge_pte_lockptr(hstate_vma(vma), mm, pte);
__migration_entry_wait(mm, pte, ptl);
}
#ifdef CONFIG_BLOCK
/* Returns true if all buffers are successfully locked */
static bool buffer_migrate_lock_buffers(struct buffer_head *head,
enum migrate_mode mode)
{
struct buffer_head *bh = head;
/* Simple case, sync compaction */
if (mode != MIGRATE_ASYNC) {
do {
get_bh(bh);
lock_buffer(bh);
bh = bh->b_this_page;
} while (bh != head);
return true;
}
/* async case, we cannot block on lock_buffer so use trylock_buffer */
do {
get_bh(bh);
if (!trylock_buffer(bh)) {
/*
* We failed to lock the buffer and cannot stall in
* async migration. Release the taken locks
*/
struct buffer_head *failed_bh = bh;
put_bh(failed_bh);
bh = head;
while (bh != failed_bh) {
unlock_buffer(bh);
put_bh(bh);
bh = bh->b_this_page;
}
return false;
}
bh = bh->b_this_page;
} while (bh != head);
return true;
}
#else
static inline bool buffer_migrate_lock_buffers(struct buffer_head *head,
enum migrate_mode mode)
{
return true;
}
#endif /* CONFIG_BLOCK */
/*
* Replace the page in the mapping.
*
* The number of remaining references must be:
* 1 for anonymous pages without a mapping
* 2 for pages with a mapping
* 3 for pages with a mapping and PagePrivate/PagePrivate2 set.
*/
int migrate_page_move_mapping(struct address_space *mapping,
struct page *newpage, struct page *page,
struct buffer_head *head, enum migrate_mode mode,
int extra_count)
{
struct zone *oldzone, *newzone;
int dirty;
int expected_count = 1 + extra_count;
void **pslot;
if (!mapping) {
/* Anonymous page without mapping */
if (page_count(page) != expected_count)
return -EAGAIN;
/* No turning back from here */
newpage->index = page->index;
newpage->mapping = page->mapping;
if (PageSwapBacked(page))
__SetPageSwapBacked(newpage);
return MIGRATEPAGE_SUCCESS;
}
oldzone = page_zone(page);
newzone = page_zone(newpage);
spin_lock_irq(&mapping->tree_lock);
pslot = radix_tree_lookup_slot(&mapping->page_tree,
page_index(page));
expected_count += 1 + page_has_private(page);
if (page_count(page) != expected_count ||
radix_tree_deref_slot_protected(pslot, &mapping->tree_lock) != page) {
spin_unlock_irq(&mapping->tree_lock);
return -EAGAIN;
}
if (!page_ref_freeze(page, expected_count)) {
spin_unlock_irq(&mapping->tree_lock);
return -EAGAIN;
}
/*
* In the async migration case of moving a page with buffers, lock the
* buffers using trylock before the mapping is moved. If the mapping
* was moved, we later failed to lock the buffers and could not move
* the mapping back due to an elevated page count, we would have to
* block waiting on other references to be dropped.
*/
if (mode == MIGRATE_ASYNC && head &&
!buffer_migrate_lock_buffers(head, mode)) {
page_ref_unfreeze(page, expected_count);
spin_unlock_irq(&mapping->tree_lock);
return -EAGAIN;
}
/*
* Now we know that no one else is looking at the page:
* no turning back from here.
*/
newpage->index = page->index;
newpage->mapping = page->mapping;
get_page(newpage); /* add cache reference */
if (PageSwapBacked(page)) {
__SetPageSwapBacked(newpage);
if (PageSwapCache(page)) {
SetPageSwapCache(newpage);
set_page_private(newpage, page_private(page));
}
} else {
VM_BUG_ON_PAGE(PageSwapCache(page), page);
}
/* Move dirty while page refs frozen and newpage not yet exposed */
dirty = PageDirty(page);
if (dirty) {
ClearPageDirty(page);
SetPageDirty(newpage);
}
radix_tree_replace_slot(&mapping->page_tree, pslot, newpage);
/*
* Drop cache reference from old page by unfreezing
* to one less reference.
* We know this isn't the last reference.
*/
page_ref_unfreeze(page, expected_count - 1);
spin_unlock(&mapping->tree_lock);
/* Leave irq disabled to prevent preemption while updating stats */
/*
* If moved to a different zone then also account
* the page for that zone. Other VM counters will be
* taken care of when we establish references to the
* new page and drop references to the old page.
*
* Note that anonymous pages are accounted for
* via NR_FILE_PAGES and NR_ANON_MAPPED if they
* are mapped to swap space.
*/
if (newzone != oldzone) {
__dec_node_state(oldzone->zone_pgdat, NR_FILE_PAGES);
__inc_node_state(newzone->zone_pgdat, NR_FILE_PAGES);
if (PageSwapBacked(page) && !PageSwapCache(page)) {
__dec_node_state(oldzone->zone_pgdat, NR_SHMEM);
__inc_node_state(newzone->zone_pgdat, NR_SHMEM);
}
if (dirty && mapping_cap_account_dirty(mapping)) {
__dec_node_state(oldzone->zone_pgdat, NR_FILE_DIRTY);
__dec_zone_state(oldzone, NR_ZONE_WRITE_PENDING);
__inc_node_state(newzone->zone_pgdat, NR_FILE_DIRTY);
__inc_zone_state(newzone, NR_ZONE_WRITE_PENDING);
}
}
local_irq_enable();
return MIGRATEPAGE_SUCCESS;
}
EXPORT_SYMBOL(migrate_page_move_mapping);
/*
* The expected number of remaining references is the same as that
* of migrate_page_move_mapping().
*/
int migrate_huge_page_move_mapping(struct address_space *mapping,
struct page *newpage, struct page *page)
{
int expected_count;
void **pslot;
spin_lock_irq(&mapping->tree_lock);
pslot = radix_tree_lookup_slot(&mapping->page_tree,
page_index(page));
expected_count = 2 + page_has_private(page);
if (page_count(page) != expected_count ||
radix_tree_deref_slot_protected(pslot, &mapping->tree_lock) != page) {
spin_unlock_irq(&mapping->tree_lock);
return -EAGAIN;
}
if (!page_ref_freeze(page, expected_count)) {
spin_unlock_irq(&mapping->tree_lock);
return -EAGAIN;
}
newpage->index = page->index;
newpage->mapping = page->mapping;
get_page(newpage);
radix_tree_replace_slot(&mapping->page_tree, pslot, newpage);
page_ref_unfreeze(page, expected_count - 1);
spin_unlock_irq(&mapping->tree_lock);
return MIGRATEPAGE_SUCCESS;
}
/*
* Gigantic pages are so large that we do not guarantee that page++ pointer
* arithmetic will work across the entire page. We need something more
* specialized.
*/
static void __copy_gigantic_page(struct page *dst, struct page *src,
int nr_pages)
{
int i;
struct page *dst_base = dst;
struct page *src_base = src;
for (i = 0; i < nr_pages; ) {
cond_resched();
copy_highpage(dst, src);
i++;
dst = mem_map_next(dst, dst_base, i);
src = mem_map_next(src, src_base, i);
}
}
static void copy_huge_page(struct page *dst, struct page *src)
{
int i;
int nr_pages;
if (PageHuge(src)) {
/* hugetlbfs page */
struct hstate *h = page_hstate(src);
nr_pages = pages_per_huge_page(h);
if (unlikely(nr_pages > MAX_ORDER_NR_PAGES)) {
__copy_gigantic_page(dst, src, nr_pages);
return;
}
} else {
/* thp page */
BUG_ON(!PageTransHuge(src));
nr_pages = hpage_nr_pages(src);
}
for (i = 0; i < nr_pages; i++) {
cond_resched();
copy_highpage(dst + i, src + i);
}
}
/*
* Copy the page to its new location
*/
void migrate_page_copy(struct page *newpage, struct page *page)
{
int cpupid;
if (PageHuge(page) || PageTransHuge(page))
copy_huge_page(newpage, page);
else
copy_highpage(newpage, page);
if (PageError(page))
SetPageError(newpage);
if (PageReferenced(page))
SetPageReferenced(newpage);
if (PageUptodate(page))
SetPageUptodate(newpage);
if (TestClearPageActive(page)) {
VM_BUG_ON_PAGE(PageUnevictable(page), page);
SetPageActive(newpage);
} else if (TestClearPageUnevictable(page))
SetPageUnevictable(newpage);
if (PageChecked(page))
SetPageChecked(newpage);
if (PageMappedToDisk(page))
SetPageMappedToDisk(newpage);
/* Move dirty on pages not done by migrate_page_move_mapping() */
if (PageDirty(page))
SetPageDirty(newpage);
if (page_is_young(page))
set_page_young(newpage);
if (page_is_idle(page))
set_page_idle(newpage);
/*
* Copy NUMA information to the new page, to prevent over-eager
* future migrations of this same page.
*/
cpupid = page_cpupid_xchg_last(page, -1);
page_cpupid_xchg_last(newpage, cpupid);
ksm_migrate_page(newpage, page);
/*
* Please do not reorder this without considering how mm/ksm.c's
* get_ksm_page() depends upon ksm_migrate_page() and PageSwapCache().
*/
if (PageSwapCache(page))
ClearPageSwapCache(page);
ClearPagePrivate(page);
set_page_private(page, 0);
/*
* If any waiters have accumulated on the new page then
* wake them up.
*/
if (PageWriteback(newpage))
end_page_writeback(newpage);
copy_page_owner(page, newpage);
mem_cgroup_migrate(page, newpage);
}
EXPORT_SYMBOL(migrate_page_copy);
/************************************************************
* Migration functions
***********************************************************/
/*
* Common logic to directly migrate a single LRU page suitable for
* pages that do not use PagePrivate/PagePrivate2.
*
* Pages are locked upon entry and exit.
*/
int migrate_page(struct address_space *mapping,
struct page *newpage, struct page *page,
enum migrate_mode mode)
{
int rc;
BUG_ON(PageWriteback(page)); /* Writeback must be complete */
rc = migrate_page_move_mapping(mapping, newpage, page, NULL, mode, 0);
if (rc != MIGRATEPAGE_SUCCESS)
return rc;
migrate_page_copy(newpage, page);
return MIGRATEPAGE_SUCCESS;
}
EXPORT_SYMBOL(migrate_page);
#ifdef CONFIG_BLOCK
/*
* Migration function for pages with buffers. This function can only be used
* if the underlying filesystem guarantees that no other references to "page"
* exist.
*/
int buffer_migrate_page(struct address_space *mapping,
struct page *newpage, struct page *page, enum migrate_mode mode)
{
struct buffer_head *bh, *head;
int rc;
if (!page_has_buffers(page))
return migrate_page(mapping, newpage, page, mode);
head = page_buffers(page);
rc = migrate_page_move_mapping(mapping, newpage, page, head, mode, 0);
if (rc != MIGRATEPAGE_SUCCESS)
return rc;
/*
* In the async case, migrate_page_move_mapping locked the buffers
* with an IRQ-safe spinlock held. In the sync case, the buffers
* need to be locked now
*/
if (mode != MIGRATE_ASYNC)
BUG_ON(!buffer_migrate_lock_buffers(head, mode));
ClearPagePrivate(page);
set_page_private(newpage, page_private(page));
set_page_private(page, 0);
put_page(page);
get_page(newpage);
bh = head;
do {
set_bh_page(bh, newpage, bh_offset(bh));
bh = bh->b_this_page;
} while (bh != head);
SetPagePrivate(newpage);
migrate_page_copy(newpage, page);
bh = head;
do {
unlock_buffer(bh);
put_bh(bh);
bh = bh->b_this_page;
} while (bh != head);
return MIGRATEPAGE_SUCCESS;
}
EXPORT_SYMBOL(buffer_migrate_page);
#endif
/*
* Writeback a page to clean the dirty state
*/
static int writeout(struct address_space *mapping, struct page *page)
{
struct writeback_control wbc = {
.sync_mode = WB_SYNC_NONE,
.nr_to_write = 1,
.range_start = 0,
.range_end = LLONG_MAX,
.for_reclaim = 1
};
int rc;
if (!mapping->a_ops->writepage)
/* No write method for the address space */
return -EINVAL;
if (!clear_page_dirty_for_io(page))
/* Someone else already triggered a write */
return -EAGAIN;
/*
* A dirty page may imply that the underlying filesystem has
* the page on some queue. So the page must be clean for
* migration. Writeout may mean we loose the lock and the
* page state is no longer what we checked for earlier.
* At this point we know that the migration attempt cannot
* be successful.
*/
remove_migration_ptes(page, page, false);
rc = mapping->a_ops->writepage(page, &wbc);
if (rc != AOP_WRITEPAGE_ACTIVATE)
/* unlocked. Relock */
lock_page(page);
return (rc < 0) ? -EIO : -EAGAIN;
}
/*
* Default handling if a filesystem does not provide a migration function.
*/
static int fallback_migrate_page(struct address_space *mapping,
struct page *newpage, struct page *page, enum migrate_mode mode)
{
if (PageDirty(page)) {
/* Only writeback pages in full synchronous migration */
if (mode != MIGRATE_SYNC)
return -EBUSY;
return writeout(mapping, page);
}
/*
* Buffers may be managed in a filesystem specific way.
* We must have no buffers or drop them.
*/
if (page_has_private(page) &&
!try_to_release_page(page, GFP_KERNEL))
return -EAGAIN;
return migrate_page(mapping, newpage, page, mode);
}
/*
* Move a page to a newly allocated page
* The page is locked and all ptes have been successfully removed.
*
* The new page will have replaced the old page if this function
* is successful.
*
* Return value:
* < 0 - error code
* MIGRATEPAGE_SUCCESS - success
*/
static int move_to_new_page(struct page *newpage, struct page *page,
enum migrate_mode mode)
{
struct address_space *mapping;
int rc = -EAGAIN;
bool is_lru = !__PageMovable(page);
VM_BUG_ON_PAGE(!PageLocked(page), page);
VM_BUG_ON_PAGE(!PageLocked(newpage), newpage);
mapping = page_mapping(page);
if (likely(is_lru)) {
if (!mapping)
rc = migrate_page(mapping, newpage, page, mode);
else if (mapping->a_ops->migratepage)
/*
* Most pages have a mapping and most filesystems
* provide a migratepage callback. Anonymous pages
* are part of swap space which also has its own
* migratepage callback. This is the most common path
* for page migration.
*/
rc = mapping->a_ops->migratepage(mapping, newpage,
page, mode);
else
rc = fallback_migrate_page(mapping, newpage,
page, mode);
} else {
/*
* In case of non-lru page, it could be released after
* isolation step. In that case, we shouldn't try migration.
*/
VM_BUG_ON_PAGE(!PageIsolated(page), page);
if (!PageMovable(page)) {
rc = MIGRATEPAGE_SUCCESS;
__ClearPageIsolated(page);
goto out;
}
rc = mapping->a_ops->migratepage(mapping, newpage,
page, mode);
WARN_ON_ONCE(rc == MIGRATEPAGE_SUCCESS &&
!PageIsolated(page));
}
/*
* When successful, old pagecache page->mapping must be cleared before
* page is freed; but stats require that PageAnon be left as PageAnon.
*/
if (rc == MIGRATEPAGE_SUCCESS) {
if (__PageMovable(page)) {
VM_BUG_ON_PAGE(!PageIsolated(page), page);
/*
* We clear PG_movable under page_lock so any compactor
* cannot try to migrate this page.
*/
__ClearPageIsolated(page);
}
/*
* Anonymous and movable page->mapping will be cleard by
* free_pages_prepare so don't reset it here for keeping
* the type to work PageAnon, for example.
*/
if (!PageMappingFlags(page))
page->mapping = NULL;
}
out:
return rc;
}
static int __unmap_and_move(struct page *page, struct page *newpage,
int force, enum migrate_mode mode)
{
int rc = -EAGAIN;
int page_was_mapped = 0;
struct anon_vma *anon_vma = NULL;
bool is_lru = !__PageMovable(page);
if (!trylock_page(page)) {
if (!force || mode == MIGRATE_ASYNC)
goto out;
/*
* It's not safe for direct compaction to call lock_page.
* For example, during page readahead pages are added locked
* to the LRU. Later, when the IO completes the pages are
* marked uptodate and unlocked. However, the queueing
* could be merging multiple pages for one bio (e.g.
* mpage_readpages). If an allocation happens for the
* second or third page, the process can end up locking
* the same page twice and deadlocking. Rather than
* trying to be clever about what pages can be locked,
* avoid the use of lock_page for direct compaction
* altogether.
*/
if (current->flags & PF_MEMALLOC)
goto out;
lock_page(page);
}
if (PageWriteback(page)) {
/*
* Only in the case of a full synchronous migration is it
* necessary to wait for PageWriteback. In the async case,
* the retry loop is too short and in the sync-light case,
* the overhead of stalling is too much
*/
if (mode != MIGRATE_SYNC) {
rc = -EBUSY;
goto out_unlock;
}
if (!force)
goto out_unlock;
wait_on_page_writeback(page);
}
/*
* By try_to_unmap(), page->mapcount goes down to 0 here. In this case,
* we cannot notice that anon_vma is freed while we migrates a page.
* This get_anon_vma() delays freeing anon_vma pointer until the end
* of migration. File cache pages are no problem because of page_lock()
* File Caches may use write_page() or lock_page() in migration, then,
* just care Anon page here.
*
* Only page_get_anon_vma() understands the subtleties of
* getting a hold on an anon_vma from outside one of its mms.
* But if we cannot get anon_vma, then we won't need it anyway,
* because that implies that the anon page is no longer mapped
* (and cannot be remapped so long as we hold the page lock).
*/
if (PageAnon(page) && !PageKsm(page))
anon_vma = page_get_anon_vma(page);
/*
* Block others from accessing the new page when we get around to
* establishing additional references. We are usually the only one
* holding a reference to newpage at this point. We used to have a BUG
* here if trylock_page(newpage) fails, but would like to allow for
* cases where there might be a race with the previous use of newpage.
* This is much like races on refcount of oldpage: just don't BUG().
*/
if (unlikely(!trylock_page(newpage)))
goto out_unlock;
if (unlikely(!is_lru)) {
rc = move_to_new_page(newpage, page, mode);
goto out_unlock_both;
}
/*
* Corner case handling:
* 1. When a new swap-cache page is read into, it is added to the LRU
* and treated as swapcache but it has no rmap yet.
* Calling try_to_unmap() against a page->mapping==NULL page will
* trigger a BUG. So handle it here.
* 2. An orphaned page (see truncate_complete_page) might have
* fs-private metadata. The page can be picked up due to memory
* offlining. Everywhere else except page reclaim, the page is
* invisible to the vm, so the page can not be migrated. So try to
* free the metadata, so the page can be freed.
*/
if (!page->mapping) {
VM_BUG_ON_PAGE(PageAnon(page), page);