rmap.c 34.3 KB
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/*
 * mm/rmap.c - physical to virtual reverse mappings
 *
 * Copyright 2001, Rik van Riel <riel@conectiva.com.br>
 * Released under the General Public License (GPL).
 *
 * Simple, low overhead reverse mapping scheme.
 * Please try to keep this thing as modular as possible.
 *
 * Provides methods for unmapping each kind of mapped page:
 * the anon methods track anonymous pages, and
 * the file methods track pages belonging to an inode.
 *
 * Original design by Rik van Riel <riel@conectiva.com.br> 2001
 * File methods by Dave McCracken <dmccr@us.ibm.com> 2003, 2004
 * Anonymous methods by Andrea Arcangeli <andrea@suse.de> 2004
 * Contributions by Hugh Dickins <hugh@veritas.com> 2003, 2004
 */

/*
 * Lock ordering in mm:
 *
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 * inode->i_mutex	(while writing or truncating, not reading or faulting)
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 *   inode->i_alloc_sem (vmtruncate_range)
 *   mm->mmap_sem
 *     page->flags PG_locked (lock_page)
 *       mapping->i_mmap_lock
 *         anon_vma->lock
 *           mm->page_table_lock or pte_lock
 *             zone->lru_lock (in mark_page_accessed, isolate_lru_page)
 *             swap_lock (in swap_duplicate, swap_info_get)
 *               mmlist_lock (in mmput, drain_mmlist and others)
 *               mapping->private_lock (in __set_page_dirty_buffers)
 *               inode_lock (in set_page_dirty's __mark_inode_dirty)
 *                 sb_lock (within inode_lock in fs/fs-writeback.c)
 *                 mapping->tree_lock (widely used, in set_page_dirty,
 *                           in arch-dependent flush_dcache_mmap_lock,
 *                           within inode_lock in __sync_single_inode)
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 */

#include <linux/mm.h>
#include <linux/pagemap.h>
#include <linux/swap.h>
#include <linux/swapops.h>
#include <linux/slab.h>
#include <linux/init.h>
#include <linux/rmap.h>
#include <linux/rcupdate.h>
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#include <linux/module.h>
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#include <linux/memcontrol.h>
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#include <linux/mmu_notifier.h>
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#include <linux/migrate.h>
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#include <asm/tlbflush.h>

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#include "internal.h"

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static struct kmem_cache *anon_vma_cachep;

static inline struct anon_vma *anon_vma_alloc(void)
{
	return kmem_cache_alloc(anon_vma_cachep, GFP_KERNEL);
}

static inline void anon_vma_free(struct anon_vma *anon_vma)
{
	kmem_cache_free(anon_vma_cachep, anon_vma);
}
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/**
 * anon_vma_prepare - attach an anon_vma to a memory region
 * @vma: the memory region in question
 *
 * This makes sure the memory mapping described by 'vma' has
 * an 'anon_vma' attached to it, so that we can associate the
 * anonymous pages mapped into it with that anon_vma.
 *
 * The common case will be that we already have one, but if
 * if not we either need to find an adjacent mapping that we
 * can re-use the anon_vma from (very common when the only
 * reason for splitting a vma has been mprotect()), or we
 * allocate a new one.
 *
 * Anon-vma allocations are very subtle, because we may have
 * optimistically looked up an anon_vma in page_lock_anon_vma()
 * and that may actually touch the spinlock even in the newly
 * allocated vma (it depends on RCU to make sure that the
 * anon_vma isn't actually destroyed).
 *
 * As a result, we need to do proper anon_vma locking even
 * for the new allocation. At the same time, we do not want
 * to do any locking for the common case of already having
 * an anon_vma.
 *
 * This must be called with the mmap_sem held for reading.
 */
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int anon_vma_prepare(struct vm_area_struct *vma)
{
	struct anon_vma *anon_vma = vma->anon_vma;

	might_sleep();
	if (unlikely(!anon_vma)) {
		struct mm_struct *mm = vma->vm_mm;
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		struct anon_vma *allocated;
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		anon_vma = find_mergeable_anon_vma(vma);
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		allocated = NULL;
		if (!anon_vma) {
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			anon_vma = anon_vma_alloc();
			if (unlikely(!anon_vma))
				return -ENOMEM;
			allocated = anon_vma;
		}
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		spin_lock(&anon_vma->lock);
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		/* page_table_lock to protect against threads */
		spin_lock(&mm->page_table_lock);
		if (likely(!vma->anon_vma)) {
			vma->anon_vma = anon_vma;
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			list_add_tail(&vma->anon_vma_node, &anon_vma->head);
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			allocated = NULL;
		}
		spin_unlock(&mm->page_table_lock);

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		spin_unlock(&anon_vma->lock);
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		if (unlikely(allocated))
			anon_vma_free(allocated);
	}
	return 0;
}

void __anon_vma_merge(struct vm_area_struct *vma, struct vm_area_struct *next)
{
	BUG_ON(vma->anon_vma != next->anon_vma);
	list_del(&next->anon_vma_node);
}

void __anon_vma_link(struct vm_area_struct *vma)
{
	struct anon_vma *anon_vma = vma->anon_vma;

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	if (anon_vma)
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		list_add_tail(&vma->anon_vma_node, &anon_vma->head);
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}

void anon_vma_link(struct vm_area_struct *vma)
{
	struct anon_vma *anon_vma = vma->anon_vma;

	if (anon_vma) {
		spin_lock(&anon_vma->lock);
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		list_add_tail(&vma->anon_vma_node, &anon_vma->head);
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		spin_unlock(&anon_vma->lock);
	}
}

void anon_vma_unlink(struct vm_area_struct *vma)
{
	struct anon_vma *anon_vma = vma->anon_vma;
	int empty;

	if (!anon_vma)
		return;

	spin_lock(&anon_vma->lock);
	list_del(&vma->anon_vma_node);

	/* We must garbage collect the anon_vma if it's empty */
	empty = list_empty(&anon_vma->head);
	spin_unlock(&anon_vma->lock);

	if (empty)
		anon_vma_free(anon_vma);
}

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static void anon_vma_ctor(void *data)
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{
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	struct anon_vma *anon_vma = data;
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	spin_lock_init(&anon_vma->lock);
	INIT_LIST_HEAD(&anon_vma->head);
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}

void __init anon_vma_init(void)
{
	anon_vma_cachep = kmem_cache_create("anon_vma", sizeof(struct anon_vma),
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			0, SLAB_DESTROY_BY_RCU|SLAB_PANIC, anon_vma_ctor);
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}

/*
 * Getting a lock on a stable anon_vma from a page off the LRU is
 * tricky: page_lock_anon_vma rely on RCU to guard against the races.
 */
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static struct anon_vma *page_lock_anon_vma(struct page *page)
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{
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	struct anon_vma *anon_vma;
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	unsigned long anon_mapping;

	rcu_read_lock();
	anon_mapping = (unsigned long) page->mapping;
	if (!(anon_mapping & PAGE_MAPPING_ANON))
		goto out;
	if (!page_mapped(page))
		goto out;

	anon_vma = (struct anon_vma *) (anon_mapping - PAGE_MAPPING_ANON);
	spin_lock(&anon_vma->lock);
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	return anon_vma;
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out:
	rcu_read_unlock();
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	return NULL;
}

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static void page_unlock_anon_vma(struct anon_vma *anon_vma)
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{
	spin_unlock(&anon_vma->lock);
	rcu_read_unlock();
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}

/*
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 * At what user virtual address is page expected in @vma?
 * Returns virtual address or -EFAULT if page's index/offset is not
 * within the range mapped the @vma.
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 */
static inline unsigned long
vma_address(struct page *page, struct vm_area_struct *vma)
{
	pgoff_t pgoff = page->index << (PAGE_CACHE_SHIFT - PAGE_SHIFT);
	unsigned long address;

	address = vma->vm_start + ((pgoff - vma->vm_pgoff) << PAGE_SHIFT);
	if (unlikely(address < vma->vm_start || address >= vma->vm_end)) {
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		/* page should be within @vma mapping range */
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		return -EFAULT;
	}
	return address;
}

/*
 * At what user virtual address is page expected in vma? checking that the
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 * page matches the vma: currently only used on anon pages, by unuse_vma;
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 */
unsigned long page_address_in_vma(struct page *page, struct vm_area_struct *vma)
{
	if (PageAnon(page)) {
		if ((void *)vma->anon_vma !=
		    (void *)page->mapping - PAGE_MAPPING_ANON)
			return -EFAULT;
	} else if (page->mapping && !(vma->vm_flags & VM_NONLINEAR)) {
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		if (!vma->vm_file ||
		    vma->vm_file->f_mapping != page->mapping)
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			return -EFAULT;
	} else
		return -EFAULT;
	return vma_address(page, vma);
}

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/*
 * Check that @page is mapped at @address into @mm.
 *
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 * If @sync is false, page_check_address may perform a racy check to avoid
 * the page table lock when the pte is not present (helpful when reclaiming
 * highly shared pages).
 *
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 * On success returns with pte mapped and locked.
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 */
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pte_t *page_check_address(struct page *page, struct mm_struct *mm,
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			  unsigned long address, spinlock_t **ptlp, int sync)
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{
	pgd_t *pgd;
	pud_t *pud;
	pmd_t *pmd;
	pte_t *pte;
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	spinlock_t *ptl;
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	pgd = pgd_offset(mm, address);
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	if (!pgd_present(*pgd))
		return NULL;

	pud = pud_offset(pgd, address);
	if (!pud_present(*pud))
		return NULL;

	pmd = pmd_offset(pud, address);
	if (!pmd_present(*pmd))
		return NULL;

	pte = pte_offset_map(pmd, address);
	/* Make a quick check before getting the lock */
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	if (!sync && !pte_present(*pte)) {
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		pte_unmap(pte);
		return NULL;
	}

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	ptl = pte_lockptr(mm, pmd);
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	spin_lock(ptl);
	if (pte_present(*pte) && page_to_pfn(page) == pte_pfn(*pte)) {
		*ptlp = ptl;
		return pte;
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	}
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	pte_unmap_unlock(pte, ptl);
	return NULL;
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}

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/**
 * page_mapped_in_vma - check whether a page is really mapped in a VMA
 * @page: the page to test
 * @vma: the VMA to test
 *
 * Returns 1 if the page is mapped into the page tables of the VMA, 0
 * if the page is not mapped into the page tables of this VMA.  Only
 * valid for normal file or anonymous VMAs.
 */
static int page_mapped_in_vma(struct page *page, struct vm_area_struct *vma)
{
	unsigned long address;
	pte_t *pte;
	spinlock_t *ptl;

	address = vma_address(page, vma);
	if (address == -EFAULT)		/* out of vma range */
		return 0;
	pte = page_check_address(page, vma->vm_mm, address, &ptl, 1);
	if (!pte)			/* the page is not in this mm */
		return 0;
	pte_unmap_unlock(pte, ptl);

	return 1;
}

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/*
 * Subfunctions of page_referenced: page_referenced_one called
 * repeatedly from either page_referenced_anon or page_referenced_file.
 */
static int page_referenced_one(struct page *page,
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	struct vm_area_struct *vma, unsigned int *mapcount)
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{
	struct mm_struct *mm = vma->vm_mm;
	unsigned long address;
	pte_t *pte;
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	spinlock_t *ptl;
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	int referenced = 0;

	address = vma_address(page, vma);
	if (address == -EFAULT)
		goto out;

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	pte = page_check_address(page, mm, address, &ptl, 0);
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	if (!pte)
		goto out;
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	/*
	 * Don't want to elevate referenced for mlocked page that gets this far,
	 * in order that it progresses to try_to_unmap and is moved to the
	 * unevictable list.
	 */
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	if (vma->vm_flags & VM_LOCKED) {
		*mapcount = 1;	/* break early from loop */
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		goto out_unmap;
	}

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	if (ptep_clear_flush_young_notify(vma, address, pte)) {
		/*
		 * Don't treat a reference through a sequentially read
		 * mapping as such.  If the page has been used in
		 * another mapping, we will catch it; if this other
		 * mapping is already gone, the unmap path will have
		 * set PG_referenced or activated the page.
		 */
		if (likely(!VM_SequentialReadHint(vma)))
			referenced++;
	}
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	/* Pretend the page is referenced if the task has the
	   swap token and is in the middle of a page fault. */
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	if (mm != current->mm && has_swap_token(mm) &&
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			rwsem_is_locked(&mm->mmap_sem))
		referenced++;

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out_unmap:
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	(*mapcount)--;
	pte_unmap_unlock(pte, ptl);
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out:
	return referenced;
}

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static int page_referenced_anon(struct page *page,
				struct mem_cgroup *mem_cont)
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{
	unsigned int mapcount;
	struct anon_vma *anon_vma;
	struct vm_area_struct *vma;
	int referenced = 0;

	anon_vma = page_lock_anon_vma(page);
	if (!anon_vma)
		return referenced;

	mapcount = page_mapcount(page);
	list_for_each_entry(vma, &anon_vma->head, anon_vma_node) {
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		/*
		 * If we are reclaiming on behalf of a cgroup, skip
		 * counting on behalf of references from different
		 * cgroups
		 */
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		if (mem_cont && !mm_match_cgroup(vma->vm_mm, mem_cont))
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			continue;
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		referenced += page_referenced_one(page, vma, &mapcount);
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		if (!mapcount)
			break;
	}
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	page_unlock_anon_vma(anon_vma);
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	return referenced;
}

/**
 * page_referenced_file - referenced check for object-based rmap
 * @page: the page we're checking references on.
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 * @mem_cont: target memory controller
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 *
 * For an object-based mapped page, find all the places it is mapped and
 * check/clear the referenced flag.  This is done by following the page->mapping
 * pointer, then walking the chain of vmas it holds.  It returns the number
 * of references it found.
 *
 * This function is only called from page_referenced for object-based pages.
 */
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static int page_referenced_file(struct page *page,
				struct mem_cgroup *mem_cont)
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{
	unsigned int mapcount;
	struct address_space *mapping = page->mapping;
	pgoff_t pgoff = page->index << (PAGE_CACHE_SHIFT - PAGE_SHIFT);
	struct vm_area_struct *vma;
	struct prio_tree_iter iter;
	int referenced = 0;

	/*
	 * The caller's checks on page->mapping and !PageAnon have made
	 * sure that this is a file page: the check for page->mapping
	 * excludes the case just before it gets set on an anon page.
	 */
	BUG_ON(PageAnon(page));

	/*
	 * The page lock not only makes sure that page->mapping cannot
	 * suddenly be NULLified by truncation, it makes sure that the
	 * structure at mapping cannot be freed and reused yet,
	 * so we can safely take mapping->i_mmap_lock.
	 */
	BUG_ON(!PageLocked(page));

	spin_lock(&mapping->i_mmap_lock);

	/*
	 * i_mmap_lock does not stabilize mapcount at all, but mapcount
	 * is more likely to be accurate if we note it after spinning.
	 */
	mapcount = page_mapcount(page);

	vma_prio_tree_foreach(vma, &iter, &mapping->i_mmap, pgoff, pgoff) {
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		/*
		 * If we are reclaiming on behalf of a cgroup, skip
		 * counting on behalf of references from different
		 * cgroups
		 */
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		if (mem_cont && !mm_match_cgroup(vma->vm_mm, mem_cont))
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			continue;
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		referenced += page_referenced_one(page, vma, &mapcount);
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		if (!mapcount)
			break;
	}

	spin_unlock(&mapping->i_mmap_lock);
	return referenced;
}

/**
 * page_referenced - test if the page was referenced
 * @page: the page to test
 * @is_locked: caller holds lock on the page
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 * @mem_cont: target memory controller
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 *
 * Quick test_and_clear_referenced for all mappings to a page,
 * returns the number of ptes which referenced the page.
 */
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int page_referenced(struct page *page, int is_locked,
			struct mem_cgroup *mem_cont)
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{
	int referenced = 0;

	if (TestClearPageReferenced(page))
		referenced++;

	if (page_mapped(page) && page->mapping) {
		if (PageAnon(page))
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			referenced += page_referenced_anon(page, mem_cont);
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		else if (is_locked)
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			referenced += page_referenced_file(page, mem_cont);
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		else if (!trylock_page(page))
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			referenced++;
		else {
			if (page->mapping)
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				referenced +=
					page_referenced_file(page, mem_cont);
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			unlock_page(page);
		}
	}
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	if (page_test_and_clear_young(page))
		referenced++;

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	return referenced;
}

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static int page_mkclean_one(struct page *page, struct vm_area_struct *vma)
{
	struct mm_struct *mm = vma->vm_mm;
	unsigned long address;
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	pte_t *pte;
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	spinlock_t *ptl;
	int ret = 0;

	address = vma_address(page, vma);
	if (address == -EFAULT)
		goto out;

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	pte = page_check_address(page, mm, address, &ptl, 1);
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	if (!pte)
		goto out;

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	if (pte_dirty(*pte) || pte_write(*pte)) {
		pte_t entry;
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		flush_cache_page(vma, address, pte_pfn(*pte));
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		entry = ptep_clear_flush_notify(vma, address, pte);
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		entry = pte_wrprotect(entry);
		entry = pte_mkclean(entry);
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		set_pte_at(mm, address, pte, entry);
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		ret = 1;
	}
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	pte_unmap_unlock(pte, ptl);
out:
	return ret;
}

static int page_mkclean_file(struct address_space *mapping, struct page *page)
{
	pgoff_t pgoff = page->index << (PAGE_CACHE_SHIFT - PAGE_SHIFT);
	struct vm_area_struct *vma;
	struct prio_tree_iter iter;
	int ret = 0;

	BUG_ON(PageAnon(page));

	spin_lock(&mapping->i_mmap_lock);
	vma_prio_tree_foreach(vma, &iter, &mapping->i_mmap, pgoff, pgoff) {
		if (vma->vm_flags & VM_SHARED)
			ret += page_mkclean_one(page, vma);
	}
	spin_unlock(&mapping->i_mmap_lock);
	return ret;
}

int page_mkclean(struct page *page)
{
	int ret = 0;

	BUG_ON(!PageLocked(page));

	if (page_mapped(page)) {
		struct address_space *mapping = page_mapping(page);
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		if (mapping) {
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			ret = page_mkclean_file(mapping, page);
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			if (page_test_dirty(page)) {
				page_clear_dirty(page);
				ret = 1;
			}
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		}
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	}

	return ret;
}
J
Jaya Kumar 已提交
586
EXPORT_SYMBOL_GPL(page_mkclean);
587

N
Nick Piggin 已提交
588
/**
R
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589
 * __page_set_anon_rmap - setup new anonymous rmap
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590 591 592 593 594 595 596 597 598 599 600 601 602 603 604
 * @page:	the page to add the mapping to
 * @vma:	the vm area in which the mapping is added
 * @address:	the user virtual address mapped
 */
static void __page_set_anon_rmap(struct page *page,
	struct vm_area_struct *vma, unsigned long address)
{
	struct anon_vma *anon_vma = vma->anon_vma;

	BUG_ON(!anon_vma);
	anon_vma = (void *) anon_vma + PAGE_MAPPING_ANON;
	page->mapping = (struct address_space *) anon_vma;

	page->index = linear_page_index(vma, address);

N
Nick Piggin 已提交
605 606 607 608
	/*
	 * nr_mapped state can be updated without turning off
	 * interrupts because it is not modified via interrupt.
	 */
609
	__inc_zone_page_state(page, NR_ANON_PAGES);
N
Nick Piggin 已提交
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}

N
Nick Piggin 已提交
612
/**
R
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613
 * __page_check_anon_rmap - sanity check anonymous rmap addition
N
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614 615 616 617 618 619 620 621 622 623 624 625 626 627 628 629 630 631 632 633 634 635 636 637 638 639 640
 * @page:	the page to add the mapping to
 * @vma:	the vm area in which the mapping is added
 * @address:	the user virtual address mapped
 */
static void __page_check_anon_rmap(struct page *page,
	struct vm_area_struct *vma, unsigned long address)
{
#ifdef CONFIG_DEBUG_VM
	/*
	 * The page's anon-rmap details (mapping and index) are guaranteed to
	 * be set up correctly at this point.
	 *
	 * We have exclusion against page_add_anon_rmap because the caller
	 * always holds the page locked, except if called from page_dup_rmap,
	 * in which case the page is already known to be setup.
	 *
	 * We have exclusion against page_add_new_anon_rmap because those pages
	 * are initially only visible via the pagetables, and the pte is locked
	 * over the call to page_add_new_anon_rmap.
	 */
	struct anon_vma *anon_vma = vma->anon_vma;
	anon_vma = (void *) anon_vma + PAGE_MAPPING_ANON;
	BUG_ON(page->mapping != (struct address_space *)anon_vma);
	BUG_ON(page->index != linear_page_index(vma, address));
#endif
}

L
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/**
 * page_add_anon_rmap - add pte mapping to an anonymous page
 * @page:	the page to add the mapping to
 * @vma:	the vm area in which the mapping is added
 * @address:	the user virtual address mapped
 *
N
Nick Piggin 已提交
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 * The caller needs to hold the pte lock and the page must be locked.
L
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 */
void page_add_anon_rmap(struct page *page,
	struct vm_area_struct *vma, unsigned long address)
{
N
Nick Piggin 已提交
652 653
	VM_BUG_ON(!PageLocked(page));
	VM_BUG_ON(address < vma->vm_start || address >= vma->vm_end);
N
Nick Piggin 已提交
654 655
	if (atomic_inc_and_test(&page->_mapcount))
		__page_set_anon_rmap(page, vma, address);
656
	else
N
Nick Piggin 已提交
657
		__page_check_anon_rmap(page, vma, address);
L
Linus Torvalds 已提交
658 659
}

R
Randy Dunlap 已提交
660
/**
N
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661 662 663 664 665 666 667
 * page_add_new_anon_rmap - add pte mapping to a new anonymous page
 * @page:	the page to add the mapping to
 * @vma:	the vm area in which the mapping is added
 * @address:	the user virtual address mapped
 *
 * Same as page_add_anon_rmap but must only be called on *new* pages.
 * This means the inc-and-test can be bypassed.
N
Nick Piggin 已提交
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 * Page does not have to be locked.
N
Nick Piggin 已提交
669 670 671 672
 */
void page_add_new_anon_rmap(struct page *page,
	struct vm_area_struct *vma, unsigned long address)
{
673
	VM_BUG_ON(address < vma->vm_start || address >= vma->vm_end);
674 675
	SetPageSwapBacked(page);
	atomic_set(&page->_mapcount, 0); /* increment count (starts at -1) */
N
Nick Piggin 已提交
676
	__page_set_anon_rmap(page, vma, address);
677
	if (page_evictable(page, vma))
678
		lru_cache_add_lru(page, LRU_ACTIVE_ANON);
679 680
	else
		add_page_to_unevictable_list(page);
N
Nick Piggin 已提交
681 682
}

L
Linus Torvalds 已提交
683 684 685 686
/**
 * page_add_file_rmap - add pte mapping to a file page
 * @page: the page to add the mapping to
 *
687
 * The caller needs to hold the pte lock.
L
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688 689 690 691
 */
void page_add_file_rmap(struct page *page)
{
	if (atomic_inc_and_test(&page->_mapcount))
692
		__inc_zone_page_state(page, NR_FILE_MAPPED);
L
Linus Torvalds 已提交
693 694
}

N
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695 696 697 698
#ifdef CONFIG_DEBUG_VM
/**
 * page_dup_rmap - duplicate pte mapping to a page
 * @page:	the page to add the mapping to
R
Randy Dunlap 已提交
699 700
 * @vma:	the vm area being duplicated
 * @address:	the user virtual address mapped
N
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701 702 703 704 705 706 707 708 709 710 711 712 713 714 715 716
 *
 * For copy_page_range only: minimal extract from page_add_file_rmap /
 * page_add_anon_rmap, avoiding unnecessary tests (already checked) so it's
 * quicker.
 *
 * The caller needs to hold the pte lock.
 */
void page_dup_rmap(struct page *page, struct vm_area_struct *vma, unsigned long address)
{
	BUG_ON(page_mapcount(page) == 0);
	if (PageAnon(page))
		__page_check_anon_rmap(page, vma, address);
	atomic_inc(&page->_mapcount);
}
#endif

L
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/**
 * page_remove_rmap - take down pte mapping from a page
 * @page: page to remove mapping from
R
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720
 * @vma: the vm area in which the mapping is removed
L
Linus Torvalds 已提交
721
 *
722
 * The caller needs to hold the pte lock.
L
Linus Torvalds 已提交
723
 */
N
Nick Piggin 已提交
724
void page_remove_rmap(struct page *page, struct vm_area_struct *vma)
L
Linus Torvalds 已提交
725 726 727
{
	if (atomic_add_negative(-1, &page->_mapcount)) {
		/*
728 729 730 731 732
		 * Now that the last pte has gone, s390 must transfer dirty
		 * flag from storage key to struct page.  We can usually skip
		 * this if the page is anon, so about to be freed; but perhaps
		 * not if it's in swapcache - there might be another pte slot
		 * containing the swap entry, but page not yet written to swap.
L
Linus Torvalds 已提交
733
		 */
734 735
		if ((!PageAnon(page) || PageSwapCache(page)) &&
		    page_test_dirty(page)) {
736
			page_clear_dirty(page);
L
Linus Torvalds 已提交
737
			set_page_dirty(page);
738
		}
739 740
		if (PageAnon(page))
			mem_cgroup_uncharge_page(page);
741
		__dec_zone_page_state(page,
742 743 744 745 746 747 748 749 750 751
			PageAnon(page) ? NR_ANON_PAGES : NR_FILE_MAPPED);
		/*
		 * It would be tidy to reset the PageAnon mapping here,
		 * but that might overwrite a racing page_add_anon_rmap
		 * which increments mapcount after us but sets mapping
		 * before us: so leave the reset to free_hot_cold_page,
		 * and remember that it's only reliable while mapped.
		 * Leaving it set also helps swapoff to reinstate ptes
		 * faster for those pages still in swapcache.
		 */
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	}
}

/*
 * Subfunctions of try_to_unmap: try_to_unmap_one called
 * repeatedly from either try_to_unmap_anon or try_to_unmap_file.
 */
759
static int try_to_unmap_one(struct page *page, struct vm_area_struct *vma,
760
				int migration)
L
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{
	struct mm_struct *mm = vma->vm_mm;
	unsigned long address;
	pte_t *pte;
	pte_t pteval;
H
Hugh Dickins 已提交
766
	spinlock_t *ptl;
L
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767 768 769 770 771 772
	int ret = SWAP_AGAIN;

	address = vma_address(page, vma);
	if (address == -EFAULT)
		goto out;

N
Nick Piggin 已提交
773
	pte = page_check_address(page, mm, address, &ptl, 0);
H
Hugh Dickins 已提交
774
	if (!pte)
N
Nikita Danilov 已提交
775
		goto out;
L
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	/*
	 * If the page is mlock()d, we cannot swap it out.
	 * If it's recently referenced (perhaps page_referenced
	 * skipped over this mm) then we should reactivate it.
	 */
N
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782 783 784 785 786 787 788 789 790 791
	if (!migration) {
		if (vma->vm_flags & VM_LOCKED) {
			ret = SWAP_MLOCK;
			goto out_unmap;
		}
		if (ptep_clear_flush_young_notify(vma, address, pte)) {
			ret = SWAP_FAIL;
			goto out_unmap;
		}
  	}
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792 793 794

	/* Nuke the page table entry. */
	flush_cache_page(vma, address, page_to_pfn(page));
A
Andrea Arcangeli 已提交
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	pteval = ptep_clear_flush_notify(vma, address, pte);
L
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796 797 798 799 800

	/* Move the dirty bit to the physical page now the pte is gone. */
	if (pte_dirty(pteval))
		set_page_dirty(page);

801 802 803
	/* Update high watermark before we lower rss */
	update_hiwater_rss(mm);

L
Linus Torvalds 已提交
804
	if (PageAnon(page)) {
H
Hugh Dickins 已提交
805
		swp_entry_t entry = { .val = page_private(page) };
806 807 808 809 810 811 812 813 814 815 816 817 818

		if (PageSwapCache(page)) {
			/*
			 * Store the swap location in the pte.
			 * See handle_pte_fault() ...
			 */
			swap_duplicate(entry);
			if (list_empty(&mm->mmlist)) {
				spin_lock(&mmlist_lock);
				if (list_empty(&mm->mmlist))
					list_add(&mm->mmlist, &init_mm.mmlist);
				spin_unlock(&mmlist_lock);
			}
819
			dec_mm_counter(mm, anon_rss);
820
		} else if (PAGE_MIGRATION) {
821 822 823 824 825 826 827
			/*
			 * Store the pfn of the page in a special migration
			 * pte. do_swap_page() will wait until the migration
			 * pte is removed and then restart fault handling.
			 */
			BUG_ON(!migration);
			entry = make_migration_entry(page, pte_write(pteval));
L
Linus Torvalds 已提交
828 829 830
		}
		set_pte_at(mm, address, pte, swp_entry_to_pte(entry));
		BUG_ON(pte_file(*pte));
831
	} else if (PAGE_MIGRATION && migration) {
832 833 834 835 836
		/* Establish migration entry for a file page */
		swp_entry_t entry;
		entry = make_migration_entry(page, pte_write(pteval));
		set_pte_at(mm, address, pte, swp_entry_to_pte(entry));
	} else
837
		dec_mm_counter(mm, file_rss);
L
Linus Torvalds 已提交
838

839

N
Nick Piggin 已提交
840
	page_remove_rmap(page, vma);
L
Linus Torvalds 已提交
841 842 843
	page_cache_release(page);

out_unmap:
H
Hugh Dickins 已提交
844
	pte_unmap_unlock(pte, ptl);
L
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845 846 847 848 849 850 851 852 853 854 855 856 857 858 859 860 861 862 863 864 865 866
out:
	return ret;
}

/*
 * objrmap doesn't work for nonlinear VMAs because the assumption that
 * offset-into-file correlates with offset-into-virtual-addresses does not hold.
 * Consequently, given a particular page and its ->index, we cannot locate the
 * ptes which are mapping that page without an exhaustive linear search.
 *
 * So what this code does is a mini "virtual scan" of each nonlinear VMA which
 * maps the file to which the target page belongs.  The ->vm_private_data field
 * holds the current cursor into that scan.  Successive searches will circulate
 * around the vma's virtual address space.
 *
 * So as more replacement pressure is applied to the pages in a nonlinear VMA,
 * more scanning pressure is placed against them as well.   Eventually pages
 * will become fully unmapped and are eligible for eviction.
 *
 * For very sparsely populated VMAs this is a little inefficient - chances are
 * there there won't be many ptes located within the scan cluster.  In this case
 * maybe we could scan further - to the end of the pte page, perhaps.
N
Nick Piggin 已提交
867 868 869 870 871
 *
 * Mlocked pages:  check VM_LOCKED under mmap_sem held for read, if we can
 * acquire it without blocking.  If vma locked, mlock the pages in the cluster,
 * rather than unmapping them.  If we encounter the "check_page" that vmscan is
 * trying to unmap, return SWAP_MLOCK, else default SWAP_AGAIN.
L
Linus Torvalds 已提交
872 873 874 875
 */
#define CLUSTER_SIZE	min(32*PAGE_SIZE, PMD_SIZE)
#define CLUSTER_MASK	(~(CLUSTER_SIZE - 1))

N
Nick Piggin 已提交
876 877
static int try_to_unmap_cluster(unsigned long cursor, unsigned int *mapcount,
		struct vm_area_struct *vma, struct page *check_page)
L
Linus Torvalds 已提交
878 879 880 881 882
{
	struct mm_struct *mm = vma->vm_mm;
	pgd_t *pgd;
	pud_t *pud;
	pmd_t *pmd;
H
Hugh Dickins 已提交
883
	pte_t *pte;
L
Linus Torvalds 已提交
884
	pte_t pteval;
H
Hugh Dickins 已提交
885
	spinlock_t *ptl;
L
Linus Torvalds 已提交
886 887 888
	struct page *page;
	unsigned long address;
	unsigned long end;
N
Nick Piggin 已提交
889 890
	int ret = SWAP_AGAIN;
	int locked_vma = 0;
L
Linus Torvalds 已提交
891 892 893 894 895 896 897 898 899 900

	address = (vma->vm_start + cursor) & CLUSTER_MASK;
	end = address + CLUSTER_SIZE;
	if (address < vma->vm_start)
		address = vma->vm_start;
	if (end > vma->vm_end)
		end = vma->vm_end;

	pgd = pgd_offset(mm, address);
	if (!pgd_present(*pgd))
N
Nick Piggin 已提交
901
		return ret;
L
Linus Torvalds 已提交
902 903 904

	pud = pud_offset(pgd, address);
	if (!pud_present(*pud))
N
Nick Piggin 已提交
905
		return ret;
L
Linus Torvalds 已提交
906 907 908

	pmd = pmd_offset(pud, address);
	if (!pmd_present(*pmd))
N
Nick Piggin 已提交
909 910 911 912 913 914 915 916 917 918 919 920
		return ret;

	/*
	 * MLOCK_PAGES => feature is configured.
	 * if we can acquire the mmap_sem for read, and vma is VM_LOCKED,
	 * keep the sem while scanning the cluster for mlocking pages.
	 */
	if (MLOCK_PAGES && down_read_trylock(&vma->vm_mm->mmap_sem)) {
		locked_vma = (vma->vm_flags & VM_LOCKED);
		if (!locked_vma)
			up_read(&vma->vm_mm->mmap_sem); /* don't need it */
	}
H
Hugh Dickins 已提交
921 922

	pte = pte_offset_map_lock(mm, pmd, address, &ptl);
L
Linus Torvalds 已提交
923

924 925 926
	/* Update high watermark before we lower rss */
	update_hiwater_rss(mm);

H
Hugh Dickins 已提交
927
	for (; address < end; pte++, address += PAGE_SIZE) {
L
Linus Torvalds 已提交
928 929
		if (!pte_present(*pte))
			continue;
930 931
		page = vm_normal_page(vma, address, *pte);
		BUG_ON(!page || PageAnon(page));
L
Linus Torvalds 已提交
932

N
Nick Piggin 已提交
933 934 935 936 937 938 939
		if (locked_vma) {
			mlock_vma_page(page);   /* no-op if already mlocked */
			if (page == check_page)
				ret = SWAP_MLOCK;
			continue;	/* don't unmap */
		}

A
Andrea Arcangeli 已提交
940
		if (ptep_clear_flush_young_notify(vma, address, pte))
L
Linus Torvalds 已提交
941 942 943
			continue;

		/* Nuke the page table entry. */
944
		flush_cache_page(vma, address, pte_pfn(*pte));
A
Andrea Arcangeli 已提交
945
		pteval = ptep_clear_flush_notify(vma, address, pte);
L
Linus Torvalds 已提交
946 947 948 949 950 951 952 953 954

		/* If nonlinear, store the file page offset in the pte. */
		if (page->index != linear_page_index(vma, address))
			set_pte_at(mm, address, pte, pgoff_to_pte(page->index));

		/* Move the dirty bit to the physical page now the pte is gone. */
		if (pte_dirty(pteval))
			set_page_dirty(page);

N
Nick Piggin 已提交
955
		page_remove_rmap(page, vma);
L
Linus Torvalds 已提交
956
		page_cache_release(page);
957
		dec_mm_counter(mm, file_rss);
L
Linus Torvalds 已提交
958 959
		(*mapcount)--;
	}
H
Hugh Dickins 已提交
960
	pte_unmap_unlock(pte - 1, ptl);
N
Nick Piggin 已提交
961 962 963
	if (locked_vma)
		up_read(&vma->vm_mm->mmap_sem);
	return ret;
L
Linus Torvalds 已提交
964 965
}

N
Nick Piggin 已提交
966 967 968 969 970 971 972 973 974 975 976 977 978 979 980 981 982 983 984 985 986 987 988 989 990 991 992 993 994 995 996 997 998 999 1000
/*
 * common handling for pages mapped in VM_LOCKED vmas
 */
static int try_to_mlock_page(struct page *page, struct vm_area_struct *vma)
{
	int mlocked = 0;

	if (down_read_trylock(&vma->vm_mm->mmap_sem)) {
		if (vma->vm_flags & VM_LOCKED) {
			mlock_vma_page(page);
			mlocked++;	/* really mlocked the page */
		}
		up_read(&vma->vm_mm->mmap_sem);
	}
	return mlocked;
}

/**
 * try_to_unmap_anon - unmap or unlock anonymous page using the object-based
 * rmap method
 * @page: the page to unmap/unlock
 * @unlock:  request for unlock rather than unmap [unlikely]
 * @migration:  unmapping for migration - ignored if @unlock
 *
 * Find all the mappings of a page using the mapping pointer and the vma chains
 * contained in the anon_vma struct it points to.
 *
 * This function is only called from try_to_unmap/try_to_munlock for
 * anonymous pages.
 * When called from try_to_munlock(), the mmap_sem of the mm containing the vma
 * where the page was found will be held for write.  So, we won't recheck
 * vm_flags for that VMA.  That should be OK, because that vma shouldn't be
 * 'LOCKED.
 */
static int try_to_unmap_anon(struct page *page, int unlock, int migration)
L
Linus Torvalds 已提交
1001 1002 1003
{
	struct anon_vma *anon_vma;
	struct vm_area_struct *vma;
N
Nick Piggin 已提交
1004
	unsigned int mlocked = 0;
L
Linus Torvalds 已提交
1005 1006
	int ret = SWAP_AGAIN;

N
Nick Piggin 已提交
1007 1008 1009
	if (MLOCK_PAGES && unlikely(unlock))
		ret = SWAP_SUCCESS;	/* default for try_to_munlock() */

L
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1010 1011 1012 1013 1014
	anon_vma = page_lock_anon_vma(page);
	if (!anon_vma)
		return ret;

	list_for_each_entry(vma, &anon_vma->head, anon_vma_node) {
N
Nick Piggin 已提交
1015 1016 1017 1018 1019 1020 1021 1022 1023 1024 1025 1026 1027 1028 1029
		if (MLOCK_PAGES && unlikely(unlock)) {
			if (!((vma->vm_flags & VM_LOCKED) &&
			      page_mapped_in_vma(page, vma)))
				continue;  /* must visit all unlocked vmas */
			ret = SWAP_MLOCK;  /* saw at least one mlocked vma */
		} else {
			ret = try_to_unmap_one(page, vma, migration);
			if (ret == SWAP_FAIL || !page_mapped(page))
				break;
		}
		if (ret == SWAP_MLOCK) {
			mlocked = try_to_mlock_page(page, vma);
			if (mlocked)
				break;	/* stop if actually mlocked page */
		}
L
Linus Torvalds 已提交
1030
	}
1031 1032

	page_unlock_anon_vma(anon_vma);
N
Nick Piggin 已提交
1033 1034 1035 1036 1037 1038

	if (mlocked)
		ret = SWAP_MLOCK;	/* actually mlocked the page */
	else if (ret == SWAP_MLOCK)
		ret = SWAP_AGAIN;	/* saw VM_LOCKED vma */

L
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1039 1040 1041 1042
	return ret;
}

/**
N
Nick Piggin 已提交
1043 1044 1045 1046
 * try_to_unmap_file - unmap/unlock file page using the object-based rmap method
 * @page: the page to unmap/unlock
 * @unlock:  request for unlock rather than unmap [unlikely]
 * @migration:  unmapping for migration - ignored if @unlock
L
Linus Torvalds 已提交
1047 1048 1049 1050
 *
 * Find all the mappings of a page using the mapping pointer and the vma chains
 * contained in the address_space struct it points to.
 *
N
Nick Piggin 已提交
1051 1052 1053 1054 1055 1056
 * This function is only called from try_to_unmap/try_to_munlock for
 * object-based pages.
 * When called from try_to_munlock(), the mmap_sem of the mm containing the vma
 * where the page was found will be held for write.  So, we won't recheck
 * vm_flags for that VMA.  That should be OK, because that vma shouldn't be
 * 'LOCKED.
L
Linus Torvalds 已提交
1057
 */
N
Nick Piggin 已提交
1058
static int try_to_unmap_file(struct page *page, int unlock, int migration)
L
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1059 1060 1061 1062 1063 1064 1065 1066 1067 1068
{
	struct address_space *mapping = page->mapping;
	pgoff_t pgoff = page->index << (PAGE_CACHE_SHIFT - PAGE_SHIFT);
	struct vm_area_struct *vma;
	struct prio_tree_iter iter;
	int ret = SWAP_AGAIN;
	unsigned long cursor;
	unsigned long max_nl_cursor = 0;
	unsigned long max_nl_size = 0;
	unsigned int mapcount;
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	unsigned int mlocked = 0;

	if (MLOCK_PAGES && unlikely(unlock))
		ret = SWAP_SUCCESS;	/* default for try_to_munlock() */
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	spin_lock(&mapping->i_mmap_lock);
	vma_prio_tree_foreach(vma, &iter, &mapping->i_mmap, pgoff, pgoff) {
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		if (MLOCK_PAGES && unlikely(unlock)) {
			if (!(vma->vm_flags & VM_LOCKED))
				continue;	/* must visit all vmas */
			ret = SWAP_MLOCK;
		} else {
			ret = try_to_unmap_one(page, vma, migration);
			if (ret == SWAP_FAIL || !page_mapped(page))
				goto out;
		}
		if (ret == SWAP_MLOCK) {
			mlocked = try_to_mlock_page(page, vma);
			if (mlocked)
				break;  /* stop if actually mlocked page */
		}
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	}

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	if (mlocked)
		goto out;

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	if (list_empty(&mapping->i_mmap_nonlinear))
		goto out;

	list_for_each_entry(vma, &mapping->i_mmap_nonlinear,
						shared.vm_set.list) {
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		if (MLOCK_PAGES && unlikely(unlock)) {
			if (!(vma->vm_flags & VM_LOCKED))
				continue;	/* must visit all vmas */
			ret = SWAP_MLOCK;	/* leave mlocked == 0 */
			goto out;		/* no need to look further */
		}
		if (!MLOCK_PAGES && !migration && (vma->vm_flags & VM_LOCKED))
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			continue;
		cursor = (unsigned long) vma->vm_private_data;
		if (cursor > max_nl_cursor)
			max_nl_cursor = cursor;
		cursor = vma->vm_end - vma->vm_start;
		if (cursor > max_nl_size)
			max_nl_size = cursor;
	}

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	if (max_nl_size == 0) {	/* all nonlinears locked or reserved ? */
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		ret = SWAP_FAIL;
		goto out;
	}

	/*
	 * We don't try to search for this page in the nonlinear vmas,
	 * and page_referenced wouldn't have found it anyway.  Instead
	 * just walk the nonlinear vmas trying to age and unmap some.
	 * The mapcount of the page we came in with is irrelevant,
	 * but even so use it as a guide to how hard we should try?
	 */
	mapcount = page_mapcount(page);
	if (!mapcount)
		goto out;
	cond_resched_lock(&mapping->i_mmap_lock);

	max_nl_size = (max_nl_size + CLUSTER_SIZE - 1) & CLUSTER_MASK;
	if (max_nl_cursor == 0)
		max_nl_cursor = CLUSTER_SIZE;

	do {
		list_for_each_entry(vma, &mapping->i_mmap_nonlinear,
						shared.vm_set.list) {
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			if (!MLOCK_PAGES && !migration &&
			    (vma->vm_flags & VM_LOCKED))
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				continue;
			cursor = (unsigned long) vma->vm_private_data;
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			while ( cursor < max_nl_cursor &&
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				cursor < vma->vm_end - vma->vm_start) {
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				ret = try_to_unmap_cluster(cursor, &mapcount,
								vma, page);
				if (ret == SWAP_MLOCK)
					mlocked = 2;	/* to return below */
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				cursor += CLUSTER_SIZE;
				vma->vm_private_data = (void *) cursor;
				if ((int)mapcount <= 0)
					goto out;
			}
			vma->vm_private_data = (void *) max_nl_cursor;
		}
		cond_resched_lock(&mapping->i_mmap_lock);
		max_nl_cursor += CLUSTER_SIZE;
	} while (max_nl_cursor <= max_nl_size);

	/*
	 * Don't loop forever (perhaps all the remaining pages are
	 * in locked vmas).  Reset cursor on all unreserved nonlinear
	 * vmas, now forgetting on which ones it had fallen behind.
	 */
1166 1167
	list_for_each_entry(vma, &mapping->i_mmap_nonlinear, shared.vm_set.list)
		vma->vm_private_data = NULL;
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out:
	spin_unlock(&mapping->i_mmap_lock);
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	if (mlocked)
		ret = SWAP_MLOCK;	/* actually mlocked the page */
	else if (ret == SWAP_MLOCK)
		ret = SWAP_AGAIN;	/* saw VM_LOCKED vma */
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	return ret;
}

/**
 * try_to_unmap - try to remove all page table mappings to a page
 * @page: the page to get unmapped
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 * @migration: migration flag
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 *
 * Tries to remove all the page table entries which are mapping this
 * page, used in the pageout path.  Caller must hold the page lock.
 * Return values are:
 *
 * SWAP_SUCCESS	- we succeeded in removing all mappings
 * SWAP_AGAIN	- we missed a mapping, try again later
 * SWAP_FAIL	- the page is unswappable
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 * SWAP_MLOCK	- page is mlocked.
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 */
1191
int try_to_unmap(struct page *page, int migration)
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{
	int ret;

	BUG_ON(!PageLocked(page));

	if (PageAnon(page))
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		ret = try_to_unmap_anon(page, 0, migration);
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	else
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		ret = try_to_unmap_file(page, 0, migration);
	if (ret != SWAP_MLOCK && !page_mapped(page))
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		ret = SWAP_SUCCESS;
	return ret;
}
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#ifdef CONFIG_UNEVICTABLE_LRU
/**
 * try_to_munlock - try to munlock a page
 * @page: the page to be munlocked
 *
 * Called from munlock code.  Checks all of the VMAs mapping the page
 * to make sure nobody else has this page mlocked. The page will be
 * returned with PG_mlocked cleared if no other vmas have it mlocked.
 *
 * Return values are:
 *
 * SWAP_SUCCESS	- no vma's holding page mlocked.
 * SWAP_AGAIN	- page mapped in mlocked vma -- couldn't acquire mmap sem
 * SWAP_MLOCK	- page is now mlocked.
 */
int try_to_munlock(struct page *page)
{
	VM_BUG_ON(!PageLocked(page) || PageLRU(page));

	if (PageAnon(page))
		return try_to_unmap_anon(page, 1, 0);
	else
		return try_to_unmap_file(page, 1, 0);
}
#endif