/*
* 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 <clameter@sgi.com>
*/
#include <linux/migrate.h>
#include <linux/module.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/pagevec.h>
#include <linux/rmap.h>
#include <linux/topology.h>
#include <linux/cpu.h>
#include <linux/cpuset.h>
#include <linux/writeback.h>
#include "internal.h"
/* The maximum number of pages to take off the LRU for migration */
#define MIGRATE_CHUNK_SIZE 256
#define lru_to_page(_head) (list_entry((_head)->prev, struct page, lru))
/*
* Isolate one page from the LRU lists. If successful put it onto
* the indicated list with elevated page count.
*
* Result:
* -EBUSY: page not on LRU list
* 0: page removed from LRU list and added to the specified list.
*/
int isolate_lru_page(struct page *page, struct list_head *pagelist)
{
int ret = -EBUSY;
if (PageLRU(page)) {
struct zone *zone = page_zone(page);
spin_lock_irq(&zone->lru_lock);
if (PageLRU(page)) {
ret = 0;
get_page(page);
ClearPageLRU(page);
if (PageActive(page))
del_page_from_active_list(zone, page);
else
del_page_from_inactive_list(zone, page);
list_add_tail(&page->lru, pagelist);
}
spin_unlock_irq(&zone->lru_lock);
}
return ret;
}
/*
* migrate_prep() needs to be called after we have compiled the list of pages
* to be migrated using isolate_lru_page() but before we begin a series of calls
* to migrate_pages().
*/
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;
}
static inline void move_to_lru(struct page *page)
{
if (PageActive(page)) {
/*
* lru_cache_add_active checks that
* the PG_active bit is off.
*/
ClearPageActive(page);
lru_cache_add_active(page);
} else {
lru_cache_add(page);
}
put_page(page);
}
/*
* Add isolated pages on the list back to the LRU.
*
* returns the number of pages put back.
*/
int putback_lru_pages(struct list_head *l)
{
struct page *page;
struct page *page2;
int count = 0;
list_for_each_entry_safe(page, page2, l, lru) {
list_del(&page->lru);
move_to_lru(page);
count++;
}
return count;
}
static inline int is_swap_pte(pte_t pte)
{
return !pte_none(pte) && !pte_present(pte) && !pte_file(pte);
}
/*
* Restore a potential migration pte to a working pte entry
*/
static void remove_migration_pte(struct vm_area_struct *vma,
struct page *old, struct page *new)
{
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;
unsigned long addr = page_address_in_vma(new, vma);
if (addr == -EFAULT)
return;
pgd = pgd_offset(mm, addr);
if (!pgd_present(*pgd))
return;
pud = pud_offset(pgd, addr);
if (!pud_present(*pud))
return;
pmd = pmd_offset(pud, addr);
if (!pmd_present(*pmd))
return;
ptep = pte_offset_map(pmd, addr);
if (!is_swap_pte(*ptep)) {
pte_unmap(ptep);
return;
}
ptl = pte_lockptr(mm, pmd);
spin_lock(ptl);
pte = *ptep;
if (!is_swap_pte(pte))
goto out;
entry = pte_to_swp_entry(pte);
if (!is_migration_entry(entry) || migration_entry_to_page(entry) != old)
goto out;
get_page(new);
pte = pte_mkold(mk_pte(new, vma->vm_page_prot));
if (is_write_migration_entry(entry))
pte = pte_mkwrite(pte);
set_pte_at(mm, addr, ptep, pte);
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, pte);
lazy_mmu_prot_update(pte);
out:
pte_unmap_unlock(ptep, ptl);
}
/*
* Note that remove_file_migration_ptes will only work on regular mappings,
* Nonlinear mappings do not use migration entries.
*/
static void remove_file_migration_ptes(struct page *old, struct page *new)
{
struct vm_area_struct *vma;
struct address_space *mapping = page_mapping(new);
struct prio_tree_iter iter;
pgoff_t pgoff = new->index << (PAGE_CACHE_SHIFT - PAGE_SHIFT);
if (!mapping)
return;
spin_lock(&mapping->i_mmap_lock);
vma_prio_tree_foreach(vma, &iter, &mapping->i_mmap, pgoff, pgoff)
remove_migration_pte(vma, old, new);
spin_unlock(&mapping->i_mmap_lock);
}
/*
* Must hold mmap_sem lock on at least one of the vmas containing
* the page so that the anon_vma cannot vanish.
*/
static void remove_anon_migration_ptes(struct page *old, struct page *new)
{
struct anon_vma *anon_vma;
struct vm_area_struct *vma;
unsigned long mapping;
mapping = (unsigned long)new->mapping;
if (!mapping || (mapping & PAGE_MAPPING_ANON) == 0)
return;
/*
* We hold the mmap_sem lock. So no need to call page_lock_anon_vma.
*/
anon_vma = (struct anon_vma *) (mapping - PAGE_MAPPING_ANON);
spin_lock(&anon_vma->lock);
list_for_each_entry(vma, &anon_vma->head, anon_vma_node)
remove_migration_pte(vma, old, new);
spin_unlock(&anon_vma->lock);
}
/*
* 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)
{
if (PageAnon(new))
remove_anon_migration_ptes(old, new);
else
remove_file_migration_ptes(old, new);
}
/*
* 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.
*
* This function is called from do_swap_page().
*/
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);
get_page(page);
pte_unmap_unlock(ptep, ptl);
wait_on_page_locked(page);
put_page(page);
return;
out:
pte_unmap_unlock(ptep, ptl);
}
/*
* 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 set.
*/
static int migrate_page_move_mapping(struct address_space *mapping,
struct page *newpage, struct page *page)
{
struct page **radix_pointer;
if (!mapping) {
/* Anonymous page */
if (page_count(page) != 1)
return -EAGAIN;
return 0;
}
write_lock_irq(&mapping->tree_lock);
radix_pointer = (struct page **)radix_tree_lookup_slot(
&mapping->page_tree,
page_index(page));
if (page_count(page) != 2 + !!PagePrivate(page) ||
*radix_pointer != page) {
write_unlock_irq(&mapping->tree_lock);
return -EAGAIN;
}
/*
* Now we know that no one else is looking at the page.
*/
get_page(newpage);
#ifdef CONFIG_SWAP
if (PageSwapCache(page)) {
SetPageSwapCache(newpage);
set_page_private(newpage, page_private(page));
}
#endif
*radix_pointer = newpage;
__put_page(page);
write_unlock_irq(&mapping->tree_lock);
return 0;
}
/*
* Copy the page to its new location
*/
static void migrate_page_copy(struct page *newpage, struct page *page)
{
copy_highpage(newpage, page);
if (PageError(page))
SetPageError(newpage);
if (PageReferenced(page))
SetPageReferenced(newpage);
if (PageUptodate(page))
SetPageUptodate(newpage);
if (PageActive(page))
SetPageActive(newpage);
if (PageChecked(page))
SetPageChecked(newpage);
if (PageMappedToDisk(page))
SetPageMappedToDisk(newpage);
if (PageDirty(page)) {
clear_page_dirty_for_io(page);
set_page_dirty(newpage);
}
#ifdef CONFIG_SWAP
ClearPageSwapCache(page);
#endif
ClearPageActive(page);
ClearPagePrivate(page);
set_page_private(page, 0);
page->mapping = NULL;
/*
* 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.
*
* Pages are locked upon entry and exit.
*/
int migrate_page(struct address_space *mapping,
struct page *newpage, struct page *page)
{
int rc;
BUG_ON(PageWriteback(page)); /* Writeback must be complete */
rc = migrate_page_move_mapping(mapping, newpage, page);
if (rc)
return rc;
migrate_page_copy(newpage, page);
return 0;
}
EXPORT_SYMBOL(migrate_page);
/*
* 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)
{
struct buffer_head *bh, *head;
int rc;
if (!page_has_buffers(page))
return migrate_page(mapping, newpage, page);
head = page_buffers(page);
rc = migrate_page_move_mapping(mapping, newpage, page);
if (rc)
return rc;
bh = head;
do {
get_bh(bh);
lock_buffer(bh);
bh = bh->b_this_page;
} while (bh != head);
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);
/*
* 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,
.nonblocking = 1,
.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 < 0)
/* I/O Error writing */
return -EIO;
if (rc != AOP_WRITEPAGE_ACTIVATE)
/* unlocked. Relock */
lock_page(page);
return -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)
{
if (PageDirty(page))
return writeout(mapping, page);
/*
* Buffers may be managed in a filesystem specific way.
* We must have no buffers or drop them.
*/
if (page_has_buffers(page) &&
!try_to_release_page(page, GFP_KERNEL))
return -EAGAIN;
return migrate_page(mapping, newpage, page);
}
/*
* 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.
*/
static int move_to_new_page(struct page *newpage, struct page *page)
{
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 (TestSetPageLocked(newpage))
BUG();
/* Prepare mapping for the new page.*/
newpage->index = page->index;
newpage->mapping = page->mapping;
mapping = page_mapping(page);
if (!mapping)
rc = migrate_page(mapping, newpage, page);
else if (mapping->a_ops->migratepage)
/*
* Most pages have a mapping and most filesystems
* should provide a migration function. Anonymous
* pages are part of swap space which also has its
* own migration function. This is the most common
* path for page migration.
*/
rc = mapping->a_ops->migratepage(mapping,
newpage, page);
else
rc = fallback_migrate_page(mapping, newpage, page);
if (!rc)
remove_migration_ptes(page, newpage);
else
newpage->mapping = NULL;
unlock_page(newpage);
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(struct page *newpage, struct page *page, int force)
{
int rc = 0;
if (page_count(page) == 1)
/* page was freed from under us. So we are done. */
goto ret;
rc = -EAGAIN;
if (TestSetPageLocked(page)) {
if (!force)
goto ret;
lock_page(page);
}
if (PageWriteback(page)) {
if (!force)
goto unlock;
wait_on_page_writeback(page);
}
/*
* Establish migration ptes or remove ptes
*/
if (try_to_unmap(page, 1) != SWAP_FAIL) {
if (!page_mapped(page))
rc = move_to_new_page(newpage, page);
} else
/* A vma has VM_LOCKED set -> permanent failure */
rc = -EPERM;
if (rc)
remove_migration_ptes(page, page);
unlock:
unlock_page(page);
ret:
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);
move_to_lru(page);
list_del(&newpage->lru);
move_to_lru(newpage);
}
return rc;
}
/*
* migrate_pages
*
* Two lists are passed to this function. The first list
* contains the pages isolated from the LRU to be migrated.
* The second list contains new pages that the isolated pages
* can be moved to.
*
* The function returns after 10 attempts or if no pages
* are movable anymore because to has become empty
* or no retryable pages exist anymore. All pages will be
* retruned to the LRU or freed.
*
* Return: Number of pages not migrated.
*/
int migrate_pages(struct list_head *from, struct list_head *to)
{
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) {
if (list_empty(to))
break;
cond_resched();
rc = unmap_and_move(lru_to_page(to), page, pass > 2);
switch(rc) {
case -EAGAIN:
retry++;
break;
case 0:
break;
default:
/* Permanent failure */
nr_failed++;
break;
}
}
}
if (!swapwrite)
current->flags &= ~PF_SWAPWRITE;
putback_lru_pages(from);
return nr_failed + retry;
}
/*
* Migrate the list 'pagelist' of pages to a certain destination.
*
* Specify destination with either non-NULL vma or dest_node >= 0
* Return the number of pages not migrated or error code
*/
int migrate_pages_to(struct list_head *pagelist,
struct vm_area_struct *vma, int dest)
{
LIST_HEAD(newlist);
int err = 0;
unsigned long offset = 0;
int nr_pages;
int nr_failed = 0;
struct page *page;
struct list_head *p;
redo:
nr_pages = 0;
list_for_each(p, pagelist) {
if (vma) {
/*
* The address passed to alloc_page_vma is used to
* generate the proper interleave behavior. We fake
* the address here by an increasing offset in order
* to get the proper distribution of pages.
*
* No decision has been made as to which page
* a certain old page is moved to so we cannot
* specify the correct address.
*/
page = alloc_page_vma(GFP_HIGHUSER, vma,
offset + vma->vm_start);
offset += PAGE_SIZE;
}
else
page = alloc_pages_node(dest, GFP_HIGHUSER, 0);
if (!page) {
err = -ENOMEM;
goto out;
}
list_add_tail(&page->lru, &newlist);
nr_pages++;
if (nr_pages > MIGRATE_CHUNK_SIZE)
break;
}
err = migrate_pages(pagelist, &newlist);
if (err >= 0) {
nr_failed += err;
if (list_empty(&newlist) && !list_empty(pagelist))
goto redo;
}
out:
/* Calculate number of leftover pages */
list_for_each(p, pagelist)
nr_failed++;
return nr_failed;
}
