path: root/mm/migrate.c

/*
 * 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/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/swapops.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)
{
	/* Must have swap device for migration */
	if (nr_swap_pages <= 0)
		return -ENODEV;

	/*
	 * 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)
{
	list_del(&page->lru);
	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) {
		move_to_lru(page);
		count++;
	}
	return count;
}

/*
 * Non migratable page
 */
int fail_migrate_page(struct page *newpage, struct page *page)
{
	return -EIO;
}
EXPORT_SYMBOL(fail_migrate_page);

/*
 * swapout a single page
 * page is locked upon entry, unlocked on exit
 */
static int swap_page(struct page *page)
{
	struct address_space *mapping = page_mapping(page);

	if (page_mapped(page) && mapping)
		if (try_to_unmap(page, 1) != SWAP_SUCCESS)
			goto unlock_retry;

	if (PageDirty(page)) {
		/* Page is dirty, try to write it out here */
		switch(pageout(page, mapping)) {
		case PAGE_KEEP:
		case PAGE_ACTIVATE:
			goto unlock_retry;

		case PAGE_SUCCESS:
			goto retry;

		case PAGE_CLEAN:
			; /* try to free the page below */
		}
	}

	if (PagePrivate(page)) {
		if (!try_to_release_page(page, GFP_KERNEL) ||
		    (!mapping && page_count(page) == 1))
			goto unlock_retry;
	}

	if (remove_mapping(mapping, page)) {
		/* Success */
		unlock_page(page);
		return 0;
	}

unlock_retry:
	unlock_page(page);

retry:
	return -EAGAIN;
}

/*
 * Remove references for a page and establish the new page with the correct
 * basic settings to be able to stop accesses to the page.
 */
int migrate_page_remove_references(struct page *newpage,
				struct page *page, int nr_refs)
{
	struct address_space *mapping = page_mapping(page);
	struct page **radix_pointer;

	/*
	 * Avoid doing any of the following work if the page count
	 * indicates that the page is in use or truncate has removed
	 * the page.
	 */
	if (!mapping || page_mapcount(page) + nr_refs != page_count(page))
		return -EAGAIN;

	/*
	 * Establish swap ptes for anonymous pages or destroy pte
	 * maps for files.
	 *
	 * In order to reestablish file backed mappings the fault handlers
	 * will take the radix tree_lock which may then be used to stop
  	 * processses from accessing this page until the new page is ready.
	 *
	 * A process accessing via a swap pte (an anonymous page) will take a
	 * page_lock on the old page which will block the process until the
	 * migration attempt is complete. At that time the PageSwapCache bit
	 * will be examined. If the page was migrated then the PageSwapCache
	 * bit will be clear and the operation to retrieve the page will be
	 * retried which will find the new page in the radix tree. Then a new
	 * direct mapping may be generated based on the radix tree contents.
	 *
	 * If the page was not migrated then the PageSwapCache bit
	 * is still set and the operation may continue.
	 */
	if (try_to_unmap(page, 1) == SWAP_FAIL)
		/* A vma has VM_LOCKED set -> permanent failure */
		return -EPERM;

	/*
	 * Give up if we were unable to remove all mappings.
	 */
	if (page_mapcount(page))
		return -EAGAIN;

	write_lock_irq(&mapping->tree_lock);

	radix_pointer = (struct page **)radix_tree_lookup_slot(
						&mapping->page_tree,
						page_index(page));

	if (!page_mapping(page) || page_count(page) != nr_refs ||
			*radix_pointer != page) {
		write_unlock_irq(&mapping->tree_lock);
		return -EAGAIN;
	}

	/*
	 * Now we know that no one else is looking at the page.
	 *
	 * Certain minimal information about a page must be available
	 * in order for other subsystems to properly handle the page if they
	 * find it through the radix tree update before we are finished
	 * copying the page.
	 */
	get_page(newpage);
	newpage->index = page->index;
	newpage->mapping = page->mapping;
	if (PageSwapCache(page)) {
		SetPageSwapCache(newpage);
		set_page_private(newpage, page_private(page));
	}

	*radix_pointer = newpage;
	__put_page(page);
	write_unlock_irq(&mapping->tree_lock);

	return 0;
}
EXPORT_SYMBOL(migrate_page_remove_references);

/*
 * Copy the page to its new location
 */
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);
 	}

	ClearPageSwapCache(page);
	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);
}
EXPORT_SYMBOL(migrate_page_copy);

/*
 * 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 page *newpage, struct page *page)
{