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/*
* Memory Migration functionality - linux/mm/migration.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 <iwamoto@valinux.co.jp>
* Hirokazu Takahashi <taka@valinux.co.jp>
* Dave Hansen <haveblue@us.ibm.com>
* 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/memcontrol.h>
#include <linux/syscalls.h>
#include <linux/hugetlb.h>
#include <linux/hugetlb_cgroup.h>
#include <linux/gfp.h>

#include <asm/tlbflush.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;
}

/*
* Add isolated pages on the list back to the LRU under page lock
* to avoid leaking evictable pages back onto unevictable list.
*/
void putback_lru_pages(struct list_head *l)
{
struct page *page;
struct page *page2;

list_for_each_entry_safe(page, page2, l, lru) {
list_del(&page->lru);
dec_zone_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 int remove_migration_pte(struct page *new, struct vm_area_struct *vma,
unsigned long addr, void *old)
{
struct mm_struct *mm = vma->vm_mm;
swp_entry_t entry;
  pgd_t *pgd;
  pud_t *pud;
  pmd_t *pmd;
pte_t *ptep, pte;
  spinlock_t *ptl;

if (unlikely(PageHuge(new))) {
ptep = huge_pte_offset(mm, addr);
if (!ptep)
goto out;
ptl = &mm->page_table_lock;
} else {
pgd = pgd_offset(mm, addr);
if (!pgd_present(*pgd))
goto out;

pud = pud_offset(pgd, addr);
if (!pud_present(*pud))
goto out;

pmd = pmd_offset(pud, addr);
if (pmd_trans_huge(*pmd))
goto out;
if (!pmd_present(*pmd))
goto out;

ptep = pte_offset_map(pmd, addr);

/*
* Peek to check is_swap_pte() before taking ptlock? No, we
* can race mremap's move_ptes(), which skips anon_vma lock.
*/

ptl = pte_lockptr(mm, pmd);
}

  spin_lock(ptl);
pte = *ptep;
if (!is_swap_pte(pte))
goto unlock;

entry = pte_to_swp_entry(pte);

if (!is_migration_entry(entry) ||
migration_entry_to_page(entry) != old)
goto unlock;

get_page(new);
pte = pte_mkold(mk_pte(new, vma->vm_page_prot));
if (is_write_migration_entry(entry))
pte = pte_mkwrite(pte);
#ifdef CONFIG_HUGETLB_PAGE
if (PageHuge(new))
pte = pte_mkhuge(pte);
#endif
flush_cache_page(vma, addr, pte_pfn(pte));
set_pte_at(mm, addr, ptep, pte);

if (PageHuge(new)) {
if (PageAnon(new))
hugepage_add_anon_rmap(new, vma, addr);
else
page_dup_rmap(new);
} else if (PageAnon(new))
page_add_anon_rmap(new, vma, addr);
else
page_add_file_rmap(new);

/* No need to invalidate - it was non-present before */
update_mmu_cache(vma, addr, ptep);
unlock:
pte_unmap_unlock(ptep, ptl);
out:
return SWAP_AGAIN;
}

/*
* Get rid of all migration entries and replace them by
* references to the indicated page.
*/
static void remove_migration_ptes(struct page *old, struct page *new)
{
rmap_walk(new, remove_migration_pte, old);
}

/*
* 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, pmd_t *pmd,
unsigned long address)
{
pte_t *ptep, pte;
spinlock_t *ptl;
swp_entry_t entry;
struct page *page;

ptep = pte_offset_map_lock(mm, pmd, address, &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);
}

#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.
*/
static int migrate_page_move_mapping(struct address_space *mapping,
struct page *newpage, struct page *page,
struct buffer_head *head, enum migrate_mode mode)
{
int expected_count;
void **pslot;

if (!mapping) {
/* Anonymous page without mapping */
if (page_count(page) != 1)
return -EAGAIN;
return 0;
}

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_freeze_refs(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_unfreeze_refs(page, expected_count);
spin_unlock_irq(&mapping->tree_lock);
return -EAGAIN;
}

/*
* Now we know that no one else is looking at the page.
*/
get_page(newpage); /* add cache reference */
if (PageSwapCache(page)) {
SetPageSwapCache(newpage);
set_page_private(newpage, page_private(page));
}

radix_tree_replace_slot(pslot, newpage);

/*
* Drop cache reference from old page by unfreezing
* to one less reference.
* We know this isn't the last reference.
*/
page_unfreeze_refs(page, expected_count - 1);

/*
* 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_PAGES if they
* are mapped to swap space.
*/
__dec_zone_page_state(page, NR_FILE_PAGES);
__inc_zone_page_state(newpage, NR_FILE_PAGES);
if (!PageSwapCache(page) && PageSwapBacked(page)) {
__dec_zone_page_state(page, NR_SHMEM);
__inc_zone_page_state(newpage, NR_SHMEM);
}
spin_unlock_irq(&mapping->tree_lock);

return 0;
}

/*
* 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;

if (!mapping) {
if (page_count(page) != 1)
return -EAGAIN;
return 0;
}

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_freeze_refs(page, expected_count)) {
spin_unlock_irq(&mapping->tree_lock);
return -EAGAIN;
}

get_page(newpage);

radix_tree_replace_slot(pslot, newpage);

page_unfreeze_refs(page, expected_count - 1);

spin_unlock_irq(&mapping->tree_lock);
return 0;
}

/*
* Copy the page to its new location
*/
void migrate_page_copy(struct page *newpage, struct page *page)
{
if (PageHuge(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(PageUnevictable(page));
SetPageActive(newpage);
} else if (TestClearPageUnevictable(page))
SetPageUnevictable(newpage);
if (PageChecked(page))
SetPageChecked(newpage);
if (PageMappedToDisk(page))
SetPageMappedToDisk(newpage);

if (PageDirty(page)) {
clear_page_dirty_for_io(page);
/*
* Want to mark the page and the radix tree as dirty, and
* redo the accounting that clear_page_dirty_for_io undid,
* but we can't use set_page_dirty because that function
* is actually a signal that all of the page has become dirty.
* Whereas only part of our page may be dirty.
*/
if (PageSwapBacked(page))
SetPageDirty(newpage);
else
__set_page_dirty_nobuffers(newpage);
  }

mlock_migrate_page(newpage, page);
ksm_migrate_page(newpage, 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);
}

/************************************************************
* Migration functions
***********************************************************/

/* Always fail migration. Used for mappings that are not movable */
int fail_migrate_page(struct address_space *mapping,
struct page *newpage, struct page *page)
{
return -EIO;
}
EXPORT_SYMBOL(fail_migrate_page);

/*
* Common logic to directly migrate a single 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);

if (rc)
return rc;

migrate_page_copy(newpage, page);
return 0;
}
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);

if (rc)
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 0;
}
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);

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
* == 0 - success
*/
static int move_to_new_page(struct page *newpage, struct page *page,
int remap_swapcache, enum migrate_mode mode)
{
struct address_space *mapping;
int rc;

/*
* Block others from accessing the page when we get around to
* establishing additional references. We are the only one
* holding a reference to the new page at this point.
*/
if (!trylock_page(newpage))
BUG();

/* Prepare mapping for the new page.*/
newpage->index = page->index;
newpage->mapping = page->mapping;
if (PageSwapBacked(page))
SetPageSwapBacked(newpage);

mapping = page_mapping(page);
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);

if (rc) {
newpage->mapping = NULL;
} else {
if (remap_swapcache)
remove_migration_ptes(page, newpage);
page->mapping = NULL;
}

unlock_page(newpage);

return rc;
}

static int __unmap_and_move(struct page *page, struct page *newpage,
int force, bool offlining, enum migrate_mode mode)
{
int rc = -EAGAIN;
int remap_swapcache = 1;
struct mem_cgroup *mem;
struct anon_vma *anon_vma = NULL;

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);
}

/*
* Only memory hotplug's offline_pages() caller has locked out KSM,
* and can safely migrate a KSM page. The other cases have skipped
* PageKsm along with PageReserved - but it is only now when we have
* the page lock that we can be certain it will not go KSM beneath us
* (KSM will not upgrade a page from PageAnon to PageKsm when it sees
* its pagecount raised, but only here do we take the page lock which
* serializes that).
*/
if (PageKsm(page) && !offlining) {
rc = -EBUSY;
goto unlock;
}

/* charge against new page */
mem_cgroup_prepare_migration(page, newpage, &mem);

if (PageWriteback(page)) {
/*
* Only in the case of a full syncronous 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 uncharge;
}
if (!force)
goto uncharge;
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.
*/
if (PageAnon(page)) {
/*
* Only page_lock_anon_vma() understands the subtleties of
* getting a hold on an anon_vma from outside one of its mms.
*/
anon_vma = page_get_anon_vma(page);
if (anon_vma) {
/*
* Anon page
*/
} else if (PageSwapCache(page)) {
/*
* We cannot be sure that the anon_vma of an unmapped
* swapcache page is safe to use because we don't
* know in advance if the VMA that this page belonged
* to still exists. If the VMA and others sharing the
* data have been freed, then the anon_vma could
* already be invalid.
*
* To avoid this possibility, swapcache pages get
* migrated but are not remapped when migration
* completes
*/
remap_swapcache = 0;
} else {
goto uncharge;
}
}

/*
* 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(PageAnon(page));
if (page_has_private(page)) {
try_to_free_buffers(page);
goto uncharge;
}
goto skip_unmap;
}

/* Establish migration ptes or remove ptes */
try_to_unmap(page, TTU_MIGRATION|TTU_IGNORE_MLOCK|TTU_IGNORE_ACCESS);

skip_unmap:
if (!page_mapped(page))
rc = move_to_new_page(newpage, page, remap_swapcache, mode);

if (rc && remap_swapcache)
remove_migration_ptes(page, page);

/* Drop an anon_vma reference if we took one */
if (anon_vma)
put_anon_vma(anon_vma);

uncharge:
mem_cgroup_end_migration(mem, page, newpage, rc == 0);
unlock:
unlock_page(page);
out:
return rc;
}

/*
* Obtain the lock on page, remove all ptes and migrate the page
* to the newly allocated page in newpage.
*/
static int unmap_and_move(new_page_t get_new_page, unsigned long private,
struct page *page, int force, bool offlining,
enum migrate_mode mode)
{
int rc = 0;
int *result = NULL;
struct page *newpage = get_new_page(page, private, &result);

if (!newpage)
return -ENOMEM;

if (page_count(page) == 1) {
/* page was freed from under us. So we are done. */
goto out;
}

if (unlikely(PageTransHuge(page)))
if (unlikely(split_huge_page(page)))
goto out;

rc = __unmap_and_move(page, newpage, force, offlining, mode);
out:
if (rc != -EAGAIN) {
/*
* A page that has been migrated has all references
* removed and will be freed. A page that has not been
* migrated will have kepts its references and be
* restored.
*/
list_del(&page->lru);
dec_zone_page_state(page, NR_ISOLATED_ANON +
page_is_file_cache(page));
putback_lru_page(page);
}
/*
* Move the new page to the LRU. If migration was not successful
* then this will free the page.
*/
putback_lru_page(newpage);
if (result) {
if (rc)
*result = rc;
else
*result = page_to_nid(newpage);
}
return rc;
}

/*
* Counterpart of unmap_and_move_page() for hugepage migration.
*
* This function doesn't wait the completion of hugepage I/O
* because there is no race between I/O and migration for hugepage.
* Note that currently hugepage I/O occurs only in direct I/O
* where no lock is held and PG_writeback is irrelevant,
* and writeback status of all subpages are counted in the reference
* count of the head page (i.e. if all subpages of a 2MB hugepage are
* under direct I/O, the reference of the head page is 512 and a bit more.)
* This means that when we try to migrate hugepage whose subpages are
* doing direct I/O, some references remain after try_to_unmap() and
* hugepage migration fails without data corruption.
*
* There is also no race when direct I/O is issued on the page under migration,
* because then pte is replaced with migration swap entry and direct I/O code
* will wait in the page fault for migration to complete.
*/
static int unmap_and_move_huge_page(new_page_t get_new_page,
unsigned long private, struct page *hpage,
int force, bool offlining,
enum migrate_mode mode)
{
int rc = 0;
int *result = NULL;
struct page *new_hpage = get_new_page(hpage, private, &result);
struct anon_vma *anon_vma = NULL;

if (!new_hpage)
return -ENOMEM;

rc = -EAGAIN;

if (!trylock_page(hpage)) {
if (!force || mode != MIGRATE_SYNC)
goto out;
lock_page(hpage);
}

if (PageAnon(hpage))
anon_vma = page_get_anon_vma(hpage);

try_to_unmap(hpage, TTU_MIGRATION|TTU_IGNORE_MLOCK|TTU_IGNORE_ACCESS);

if (!page_mapped(hpage))
rc = move_to_new_page(new_hpage, hpage, 1, mode);

if (rc)
remove_migration_ptes(hpage, hpage);

if (anon_vma)
put_anon_vma(anon_vma);

if (!rc)
hugetlb_cgroup_migrate(hpage, new_hpage);

unlock_page(hpage);
out:
put_page(new_hpage);
if (result) {
if (rc)
*result = rc;
else
*result = page_to_nid(new_hpage);
}
return rc;
}

/*
* migrate_pages
*
* The function takes one list of pages to migrate and a function
* that determines from the page to be migrated and the private data
* the target of the move and allocates the page.
*
* The function returns after 10 attempts or if no pages
* are movable anymore because to has become empty
* or no retryable pages exist anymore.
* Caller should call putback_lru_pages to return pages to the LRU
* or free list only if ret != 0.
*
* Return: Number of pages not migrated or error code.
*/
int migrate_pages(struct list_head *from,
new_page_t get_new_page, unsigned long private, bool offlining,
enum migrate_mode mode)
{
int retry = 1;
int nr_failed = 0;
int pass = 0;
struct page *page;
struct page *page2;
int swapwrite = current->flags & PF_SWAPWRITE;
int rc;

if (!swapwrite)
current->flags |= PF_SWAPWRITE;

for(pass = 0; pass < 10 && retry; pass++) {
retry = 0;

list_for_each_entry_safe(page, page2, from, lru) {
cond_resched();

rc = unmap_and_move(get_new_page, private,
page, pass > 2, offlining,
mode);

switch(rc) {
case -ENOMEM:
goto out;
case -EAGAIN:
retry++;
break;
case 0:
break;
default:
/* Permanent failure */
nr_failed++;
break;
}
}
}
rc = 0;
out:
if (!swapwrite)
current->flags &= ~PF_SWAPWRITE;

if (rc)
return rc;

return nr_failed + retry;
}

int migrate_huge_page(struct page *hpage, new_page_t get_new_page,
unsigned long private, bool offlining,
enum migrate_mode mode)
{
int pass, rc;

for (pass = 0; pass < 10; pass++) {
rc = unmap_and_move_huge_page(get_new_page,
private, hpage, pass > 2, offlining,
mode);
switch (rc) {
case -ENOMEM:
goto out;
case -EAGAIN:
/* try again */
cond_resched();
break;
case 0:
goto out;
default:
rc = -EIO;
goto out;
}
}
out:
return rc;
}

#ifdef CONFIG_NUMA
/*
* Move a list of individual pages
*/
struct page_to_node {
unsigned long addr;
struct page *page;
int node;
int status;
};

static struct page *new_page_node(struct page *p, unsigned long private,
int **result)
{
struct page_to_node *pm = (struct page_to_node *)private;

while (pm->node != MAX_NUMNODES && pm->page != p)
pm++;

if (pm->node == MAX_NUMNODES)
return NULL;

*result = &pm->status;

return alloc_pages_exact_node(pm->node,
GFP_HIGHUSER_MOVABLE | GFP_THISNODE, 0);
}

/*
* Move a set of pages as indicated in the pm array. The addr
* field must be set to the virtual address of the page to be moved
* and the node number must contain a valid target node.
* The pm array ends with node = MAX_NUMNODES.
*/
static int do_move_page_to_node_array(struct mm_struct *mm,
struct page_to_node *pm,
int migrate_all)
{
int err;
struct page_to_node *pp;
LIST_HEAD(pagelist);

down_read(&mm->mmap_sem);

/*
* Build a list of pages to migrate
*/
for (pp = pm; pp->node != MAX_NUMNODES; pp++) {
struct vm_area_struct *vma;
struct page *page;

err = -EFAULT;
vma = find_vma(mm, pp->addr);
if (!vma || pp->addr < vma->vm_start || !vma_migratable(vma))
goto set_status;

page = follow_page(vma, pp->addr, FOLL_GET|FOLL_SPLIT);

err = PTR_ERR(page);
if (IS_ERR(page))
goto set_status;

err = -ENOENT;
if (!page)
goto set_status;

/* Use PageReserved to check for zero page */
if (PageReserved(page) || PageKsm(page))
goto put_and_set;

pp->page = page;
err = page_to_nid(page);

if (err == pp->node)
/*
* Node already in the right place
*/
goto put_and_set;

err = -EACCES;
if (page_mapcount(page) > 1 &&
!migrate_all)
goto put_and_set;

err = isolate_lru_page(page);
if (!err) {
list_add_tail(&page->lru, &pagelist);
inc_zone_page_state(page, NR_ISOLATED_ANON +
page_is_file_cache(page));
}
put_and_set:
/*
* Either remove the duplicate refcount from
* isolate_lru_page() or drop the page ref if it was
* not isolated.
*/
put_page(page);
set_status:
pp->status = err;
}

err = 0;
if (!list_empty(&pagelist)) {
err = migrate_pages(&pagelist, new_page_node,
(unsigned long)pm, 0, MIGRATE_SYNC);
if (err)
putback_lru_pages(&pagelist);
}

up_read(&mm->mmap_sem);
return err;
}

/*
* Migrate an array of page address onto an array of nodes and fill
* the corresponding array of status.
*/
static int do_pages_move(struct mm_struct *mm, nodemask_t task_nodes,
unsigned long nr_pages,
const void __user * __user *pages,
const int __user *nodes,
int __user *status, int flags)
{
struct page_to_node *pm;
unsigned long chunk_nr_pages;
unsigned long chunk_start;
int err;

err = -ENOMEM;
pm = (struct page_to_node *)__get_free_page(GFP_KERNEL);
if (!pm)
goto out;

migrate_prep();

/*
* Store a chunk of page_to_node array in a page,
* but keep the last one as a marker
*/
chunk_nr_pages = (PAGE_SIZE / sizeof(struct page_to_node)) - 1;

for (chunk_start = 0;
chunk_start < nr_pages;
chunk_start += chunk_nr_pages) {
int j;

if (chunk_start + chunk_nr_pages > nr_pages)
chunk_nr_pages = nr_pages - chunk_start;

/* fill the chunk pm with addrs and nodes from user-space */
for (j = 0; j < chunk_nr_pages; j++) {
const void __user *p;
int node;

err = -EFAULT;
if (get_user(p, pages + j + chunk_start))
goto out_pm;
pm[j].addr = (unsigned long) p;

if (get_user(node, nodes + j + chunk_start))
goto out_pm;

err = -ENODEV;
if (node < 0 || node >= MAX_NUMNODES)
goto out_pm;

if (!node_state(node, N_HIGH_MEMORY))
goto out_pm;

err = -EACCES;
if (!node_isset(node, task_nodes))
goto out_pm;

pm[j].node = node;
}

/* End marker for this chunk */
pm[chunk_nr_pages].node = MAX_NUMNODES;

/* Migrate this chunk */
err = do_move_page_to_node_array(mm, pm,
flags & MPOL_MF_MOVE_ALL);
if (err < 0)
goto out_pm;

/* Return status information */
for (j = 0; j < chunk_nr_pages; j++)
if (put_user(pm[j].status, status + j + chunk_start)) {
err = -EFAULT;
goto out_pm;
}
}
err = 0;

out_pm:
free_page((unsigned long)pm);
out:
return err;
}

/*
* Determine the nodes of an array of pages and store it in an array of status.
*/
static void do_pages_stat_array(struct mm_struct *mm, unsigned long nr_pages,
const void __user **pages, int *status)
{
unsigned long i;

down_read(&mm->mmap_sem);

for (i = 0; i < nr_pages; i++) {
unsigned long addr = (unsigned long)(*pages);
struct vm_area_struct *vma;
struct page *page;
int err = -EFAULT;

vma = find_vma(mm, addr);
if (!vma || addr < vma->vm_start)
goto set_status;

page = follow_page(vma, addr, 0);

err = PTR_ERR(page);
if (IS_ERR(page))
goto set_status;

err = -ENOENT;
/* Use PageReserved to check for zero page */
if (!page || PageReserved(page) || PageKsm(page))
goto set_status;

err = page_to_nid(page);
set_status:
*status = err;

pages++;
status++;
}

up_read(&mm->mmap_sem);
}

/*
* Determine the nodes of a user array of pages and store it in
* a user array of status.
*/
static int do_pages_stat(struct mm_struct *mm, unsigned long nr_pages,
const void __user * __user *pages,
int __user *status)
{
#define DO_PAGES_STAT_CHUNK_NR 16
const void __user *chunk_pages[DO_PAGES_STAT_CHUNK_NR];
int chunk_status[DO_PAGES_STAT_CHUNK_NR];

while (nr_pages) {
unsigned long chunk_nr;

chunk_nr = nr_pages;
if (chunk_nr > DO_PAGES_STAT_CHUNK_NR)
chunk_nr = DO_PAGES_STAT_CHUNK_NR;

if (copy_from_user(chunk_pages, pages, chunk_nr * sizeof(*chunk_pages)))
break;

do_pages_stat_array(mm, chunk_nr, chunk_pages, chunk_status);

if (copy_to_user(status, chunk_status, chunk_nr * sizeof(*status)))
break;

pages += chunk_nr;
status += chunk_nr;
nr_pages -= chunk_nr;
}
return nr_pages ? -EFAULT : 0;
}

/*
* Move a list of pages in the address space of the currently executing
* process.
*/
SYSCALL_DEFINE6(move_pages, pid_t, pid, unsigned long, nr_pages,
const void __user * __user *, pages,
const int __user *, nodes,
int __user *, status, int, flags)
{
const struct cred *cred = current_cred(), *tcred;
struct task_struct *task;
struct mm_struct *mm;
int err;
nodemask_t task_nodes;

/* Check flags */
if (flags & ~(MPOL_MF_MOVE|MPOL_MF_MOVE_ALL))
return -EINVAL;

if ((flags & MPOL_MF_MOVE_ALL) && !capable(CAP_SYS_NICE))
return -EPERM;

/* Find the mm_struct */
rcu_read_lock();
task = pid ? find_task_by_vpid(pid) : current;
if (!task) {
rcu_read_unlock();
return -ESRCH;
}
get_task_struct(task);

/*
* Check if this process has the right to modify the specified
* process. The right exists if the process has administrative
* capabilities, superuser privileges or the same
* userid as the target process.
*/
tcred = __task_cred(task);
if (!uid_eq(cred->euid, tcred->suid) && !uid_eq(cred->euid, tcred->uid) &&
!uid_eq(cred->uid, tcred->suid) && !uid_eq(cred->uid, tcred->uid) &&
!capable(CAP_SYS_NICE)) {
rcu_read_unlock();
err = -EPERM;
goto out;
}
rcu_read_unlock();

  err = security_task_movememory(task);
  if (err)
goto out;

task_nodes = cpuset_mems_allowed(task);
mm = get_task_mm(task);
put_task_struct(task);

if (!mm)
return -EINVAL;

if (nodes)
err = do_pages_move(mm, task_nodes, nr_pages, pages,
nodes, status, flags);
else
err = do_pages_stat(mm, nr_pages, pages, status);

mmput(mm);
return err;

out:
put_task_struct(task);
return err;
}

/*
* Call migration functions in the vma_ops that may prepare
* memory in a vm for migration. migration functions may perform
* the migration for vmas that do not have an underlying page struct.
*/
int migrate_vmas(struct mm_struct *mm, const nodemask_t *to,
const nodemask_t *from, unsigned long flags)
{
  struct vm_area_struct *vma;
  int err = 0;

for (vma = mm->mmap; vma && !err; vma = vma->vm_next) {
  if (vma->vm_ops && vma->vm_ops->migrate) {
  err = vma->vm_ops->migrate(vma, to, from, flags);
  if (err)
  break;
  }
  }
  return err;
}
#endif
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