rmap.c 42.4 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
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 * Contributions by Hugh Dickins 2003, 2004
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 */

/*
 * 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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 *
 * (code doesn't rely on that order so it could be switched around)
 * ->tasklist_lock
 *   anon_vma->lock      (memory_failure, collect_procs_anon)
 *     pte map lock
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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>
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#include <linux/ksm.h>
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#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;
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static struct kmem_cache *anon_vma_chain_cachep;
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static inline struct anon_vma *anon_vma_alloc(void)
{
	return kmem_cache_alloc(anon_vma_cachep, GFP_KERNEL);
}

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void anon_vma_free(struct anon_vma *anon_vma)
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{
	kmem_cache_free(anon_vma_cachep, anon_vma);
}
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static inline struct anon_vma_chain *anon_vma_chain_alloc(void)
{
	return kmem_cache_alloc(anon_vma_chain_cachep, GFP_KERNEL);
}

void anon_vma_chain_free(struct anon_vma_chain *anon_vma_chain)
{
	kmem_cache_free(anon_vma_chain_cachep, anon_vma_chain);
}

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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;
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	struct anon_vma_chain *avc;
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	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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		avc = anon_vma_chain_alloc();
		if (!avc)
			goto out_enomem;

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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))
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				goto out_enomem_free_avc;
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			allocated = anon_vma;
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			/*
			 * This VMA had no anon_vma yet.  This anon_vma is
			 * the root of any anon_vma tree that might form.
			 */
			anon_vma->root = anon_vma;
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		}

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		anon_vma_lock(anon_vma);
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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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			avc->anon_vma = anon_vma;
			avc->vma = vma;
			list_add(&avc->same_vma, &vma->anon_vma_chain);
			list_add(&avc->same_anon_vma, &anon_vma->head);
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			allocated = NULL;
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			avc = NULL;
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		}
		spin_unlock(&mm->page_table_lock);
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		anon_vma_unlock(anon_vma);
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		if (unlikely(allocated))
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			anon_vma_free(allocated);
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		if (unlikely(avc))
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			anon_vma_chain_free(avc);
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	}
	return 0;
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 out_enomem_free_avc:
	anon_vma_chain_free(avc);
 out_enomem:
	return -ENOMEM;
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}

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static void anon_vma_chain_link(struct vm_area_struct *vma,
				struct anon_vma_chain *avc,
				struct anon_vma *anon_vma)
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{
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	avc->vma = vma;
	avc->anon_vma = anon_vma;
	list_add(&avc->same_vma, &vma->anon_vma_chain);

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	anon_vma_lock(anon_vma);
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	list_add_tail(&avc->same_anon_vma, &anon_vma->head);
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	anon_vma_unlock(anon_vma);
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}

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/*
 * Attach the anon_vmas from src to dst.
 * Returns 0 on success, -ENOMEM on failure.
 */
int anon_vma_clone(struct vm_area_struct *dst, struct vm_area_struct *src)
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{
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	struct anon_vma_chain *avc, *pavc;

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	list_for_each_entry_reverse(pavc, &src->anon_vma_chain, same_vma) {
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		avc = anon_vma_chain_alloc();
		if (!avc)
			goto enomem_failure;
		anon_vma_chain_link(dst, avc, pavc->anon_vma);
	}
	return 0;
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 enomem_failure:
	unlink_anon_vmas(dst);
	return -ENOMEM;
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}

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/*
 * Attach vma to its own anon_vma, as well as to the anon_vmas that
 * the corresponding VMA in the parent process is attached to.
 * Returns 0 on success, non-zero on failure.
 */
int anon_vma_fork(struct vm_area_struct *vma, struct vm_area_struct *pvma)
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{
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	struct anon_vma_chain *avc;
	struct anon_vma *anon_vma;
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	/* Don't bother if the parent process has no anon_vma here. */
	if (!pvma->anon_vma)
		return 0;

	/*
	 * First, attach the new VMA to the parent VMA's anon_vmas,
	 * so rmap can find non-COWed pages in child processes.
	 */
	if (anon_vma_clone(vma, pvma))
		return -ENOMEM;

	/* Then add our own anon_vma. */
	anon_vma = anon_vma_alloc();
	if (!anon_vma)
		goto out_error;
	avc = anon_vma_chain_alloc();
	if (!avc)
		goto out_error_free_anon_vma;
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	/*
	 * The root anon_vma's spinlock is the lock actually used when we
	 * lock any of the anon_vmas in this anon_vma tree.
	 */
	anon_vma->root = pvma->anon_vma->root;
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	/*
	 * With KSM refcounts, an anon_vma can stay around longer than the
	 * process it belongs to.  The root anon_vma needs to be pinned
	 * until this anon_vma is freed, because the lock lives in the root.
	 */
	get_anon_vma(anon_vma->root);
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	/* Mark this anon_vma as the one where our new (COWed) pages go. */
	vma->anon_vma = anon_vma;
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	anon_vma_chain_link(vma, avc, anon_vma);
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	return 0;

 out_error_free_anon_vma:
	anon_vma_free(anon_vma);
 out_error:
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	unlink_anon_vmas(vma);
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	return -ENOMEM;
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}

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static void anon_vma_unlink(struct anon_vma_chain *anon_vma_chain)
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{
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	struct anon_vma *anon_vma = anon_vma_chain->anon_vma;
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	int empty;

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	/* If anon_vma_fork fails, we can get an empty anon_vma_chain. */
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	if (!anon_vma)
		return;

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	anon_vma_lock(anon_vma);
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	list_del(&anon_vma_chain->same_anon_vma);
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	/* We must garbage collect the anon_vma if it's empty */
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	empty = list_empty(&anon_vma->head) && !anonvma_external_refcount(anon_vma);
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	anon_vma_unlock(anon_vma);
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	if (empty) {
		/* We no longer need the root anon_vma */
		if (anon_vma->root != anon_vma)
			drop_anon_vma(anon_vma->root);
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		anon_vma_free(anon_vma);
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	}
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}

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void unlink_anon_vmas(struct vm_area_struct *vma)
{
	struct anon_vma_chain *avc, *next;

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	/*
	 * Unlink each anon_vma chained to the VMA.  This list is ordered
	 * from newest to oldest, ensuring the root anon_vma gets freed last.
	 */
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	list_for_each_entry_safe(avc, next, &vma->anon_vma_chain, same_vma) {
		anon_vma_unlink(avc);
		list_del(&avc->same_vma);
		anon_vma_chain_free(avc);
	}
}

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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);
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	anonvma_external_refcount_init(anon_vma);
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	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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	anon_vma_chain_cachep = KMEM_CACHE(anon_vma_chain, SLAB_PANIC);
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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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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();
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	anon_mapping = (unsigned long) ACCESS_ONCE(page->mapping);
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	if ((anon_mapping & PAGE_MAPPING_FLAGS) != PAGE_MAPPING_ANON)
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		goto out;
	if (!page_mapped(page))
		goto out;

	anon_vma = (struct anon_vma *) (anon_mapping - PAGE_MAPPING_ANON);
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	anon_vma_lock(anon_vma);
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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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void page_unlock_anon_vma(struct anon_vma *anon_vma)
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{
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	anon_vma_unlock(anon_vma);
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	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;
}

/*
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 * At what user virtual address is page expected in vma?
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 * Caller should check the page is actually part of the vma.
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 */
unsigned long page_address_in_vma(struct page *page, struct vm_area_struct *vma)
{
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	if (PageAnon(page))
		;
	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.
 */
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int page_mapped_in_vma(struct page *page, struct vm_area_struct *vma)
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{
	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.
 */
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int page_referenced_one(struct page *page, struct vm_area_struct *vma,
			unsigned long address, unsigned int *mapcount,
			unsigned long *vm_flags)
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{
	struct mm_struct *mm = vma->vm_mm;
	pte_t *pte;
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	spinlock_t *ptl;
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	int referenced = 0;

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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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		*vm_flags |= VM_LOCKED;
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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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	if (referenced)
		*vm_flags |= vma->vm_flags;
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out:
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	return referenced;
}

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static int page_referenced_anon(struct page *page,
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				struct mem_cgroup *mem_cont,
				unsigned long *vm_flags)
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{
	unsigned int mapcount;
	struct anon_vma *anon_vma;
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	struct anon_vma_chain *avc;
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	int referenced = 0;

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

	mapcount = page_mapcount(page);
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	list_for_each_entry(avc, &anon_vma->head, same_anon_vma) {
		struct vm_area_struct *vma = avc->vma;
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		unsigned long address = vma_address(page, vma);
		if (address == -EFAULT)
			continue;
526 527 528 529 530
		/*
		 * If we are reclaiming on behalf of a cgroup, skip
		 * counting on behalf of references from different
		 * cgroups
		 */
531
		if (mem_cont && !mm_match_cgroup(vma->vm_mm, mem_cont))
532
			continue;
H
Hugh Dickins 已提交
533
		referenced += page_referenced_one(page, vma, address,
534
						  &mapcount, vm_flags);
L
Linus Torvalds 已提交
535 536 537
		if (!mapcount)
			break;
	}
538 539

	page_unlock_anon_vma(anon_vma);
L
Linus Torvalds 已提交
540 541 542 543 544 545
	return referenced;
}

/**
 * page_referenced_file - referenced check for object-based rmap
 * @page: the page we're checking references on.
R
Randy Dunlap 已提交
546
 * @mem_cont: target memory controller
547
 * @vm_flags: collect encountered vma->vm_flags who actually referenced the page
L
Linus Torvalds 已提交
548 549 550 551 552 553 554 555
 *
 * 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.
 */
556
static int page_referenced_file(struct page *page,
557 558
				struct mem_cgroup *mem_cont,
				unsigned long *vm_flags)
L
Linus Torvalds 已提交
559 560 561 562 563 564 565 566 567 568 569 570 571 572 573 574 575 576 577 578 579 580 581 582 583 584 585 586 587 588 589 590
{
	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) {
H
Hugh Dickins 已提交
591 592 593
		unsigned long address = vma_address(page, vma);
		if (address == -EFAULT)
			continue;
594 595 596 597 598
		/*
		 * If we are reclaiming on behalf of a cgroup, skip
		 * counting on behalf of references from different
		 * cgroups
		 */
599
		if (mem_cont && !mm_match_cgroup(vma->vm_mm, mem_cont))
600
			continue;
H
Hugh Dickins 已提交
601
		referenced += page_referenced_one(page, vma, address,
602
						  &mapcount, vm_flags);
L
Linus Torvalds 已提交
603 604 605 606 607 608 609 610 611 612 613 614
		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
R
Randy Dunlap 已提交
615
 * @mem_cont: target memory controller
616
 * @vm_flags: collect encountered vma->vm_flags who actually referenced the page
L
Linus Torvalds 已提交
617 618 619 620
 *
 * Quick test_and_clear_referenced for all mappings to a page,
 * returns the number of ptes which referenced the page.
 */
621 622 623 624
int page_referenced(struct page *page,
		    int is_locked,
		    struct mem_cgroup *mem_cont,
		    unsigned long *vm_flags)
L
Linus Torvalds 已提交
625 626
{
	int referenced = 0;
H
Hugh Dickins 已提交
627
	int we_locked = 0;
L
Linus Torvalds 已提交
628

629
	*vm_flags = 0;
H
Hugh Dickins 已提交
630
	if (page_mapped(page) && page_rmapping(page)) {
H
Hugh Dickins 已提交
631 632 633 634 635 636 637 638 639 640 641
		if (!is_locked && (!PageAnon(page) || PageKsm(page))) {
			we_locked = trylock_page(page);
			if (!we_locked) {
				referenced++;
				goto out;
			}
		}
		if (unlikely(PageKsm(page)))
			referenced += page_referenced_ksm(page, mem_cont,
								vm_flags);
		else if (PageAnon(page))
642 643
			referenced += page_referenced_anon(page, mem_cont,
								vm_flags);
H
Hugh Dickins 已提交
644
		else if (page->mapping)
645 646
			referenced += page_referenced_file(page, mem_cont,
								vm_flags);
H
Hugh Dickins 已提交
647
		if (we_locked)
L
Linus Torvalds 已提交
648 649
			unlock_page(page);
	}
H
Hugh Dickins 已提交
650
out:
651 652 653
	if (page_test_and_clear_young(page))
		referenced++;

L
Linus Torvalds 已提交
654 655 656
	return referenced;
}

H
Hugh Dickins 已提交
657 658
static int page_mkclean_one(struct page *page, struct vm_area_struct *vma,
			    unsigned long address)
659 660
{
	struct mm_struct *mm = vma->vm_mm;
661
	pte_t *pte;
662 663 664
	spinlock_t *ptl;
	int ret = 0;

N
Nick Piggin 已提交
665
	pte = page_check_address(page, mm, address, &ptl, 1);
666 667 668
	if (!pte)
		goto out;

669 670
	if (pte_dirty(*pte) || pte_write(*pte)) {
		pte_t entry;
671

672
		flush_cache_page(vma, address, pte_pfn(*pte));
A
Andrea Arcangeli 已提交
673
		entry = ptep_clear_flush_notify(vma, address, pte);
674 675
		entry = pte_wrprotect(entry);
		entry = pte_mkclean(entry);
676
		set_pte_at(mm, address, pte, entry);
677 678
		ret = 1;
	}
679 680 681 682 683 684 685 686 687 688 689 690 691 692 693 694 695

	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) {
H
Hugh Dickins 已提交
696 697 698 699 700 701
		if (vma->vm_flags & VM_SHARED) {
			unsigned long address = vma_address(page, vma);
			if (address == -EFAULT)
				continue;
			ret += page_mkclean_one(page, vma, address);
		}
702 703 704 705 706 707 708 709 710 711 712 713 714
	}
	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);
715
		if (mapping) {
716
			ret = page_mkclean_file(mapping, page);
717 718 719 720
			if (page_test_dirty(page)) {
				page_clear_dirty(page);
				ret = 1;
			}
721
		}
722 723 724 725
	}

	return ret;
}
J
Jaya Kumar 已提交
726
EXPORT_SYMBOL_GPL(page_mkclean);
727

728 729 730 731 732 733 734 735 736 737 738 739 740 741 742 743 744 745 746 747 748 749 750 751
/**
 * page_move_anon_rmap - move a page to our anon_vma
 * @page:	the page to move to our anon_vma
 * @vma:	the vma the page belongs to
 * @address:	the user virtual address mapped
 *
 * When a page belongs exclusively to one process after a COW event,
 * that page can be moved into the anon_vma that belongs to just that
 * process, so the rmap code will not search the parent or sibling
 * processes.
 */
void page_move_anon_rmap(struct page *page,
	struct vm_area_struct *vma, unsigned long address)
{
	struct anon_vma *anon_vma = vma->anon_vma;

	VM_BUG_ON(!PageLocked(page));
	VM_BUG_ON(!anon_vma);
	VM_BUG_ON(page->index != linear_page_index(vma, address));

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

N
Nick Piggin 已提交
752
/**
R
Randy Dunlap 已提交
753
 * __page_set_anon_rmap - setup new anonymous rmap
N
Nick Piggin 已提交
754 755 756
 * @page:	the page to add the mapping to
 * @vma:	the vm area in which the mapping is added
 * @address:	the user virtual address mapped
757
 * @exclusive:	the page is exclusively owned by the current process
N
Nick Piggin 已提交
758 759
 */
static void __page_set_anon_rmap(struct page *page,
760
	struct vm_area_struct *vma, unsigned long address, int exclusive)
N
Nick Piggin 已提交
761
{
762
	struct anon_vma *anon_vma = vma->anon_vma;
763

764
	BUG_ON(!anon_vma);
765 766

	/*
767 768 769
	 * If the page isn't exclusively mapped into this vma,
	 * we must use the _oldest_ possible anon_vma for the
	 * page mapping!
770
	 *
771 772
	 * So take the last AVC chain entry in the vma, which is
	 * the deepest ancestor, and use the anon_vma from that.
773
	 */
774 775 776 777 778
	if (!exclusive) {
		struct anon_vma_chain *avc;
		avc = list_entry(vma->anon_vma_chain.prev, struct anon_vma_chain, same_vma);
		anon_vma = avc->anon_vma;
	}
N
Nick Piggin 已提交
779 780 781 782 783 784

	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
785
/**
R
Randy Dunlap 已提交
786
 * __page_check_anon_rmap - sanity check anonymous rmap addition
N
Nick Piggin 已提交
787 788 789 790 791 792 793 794 795 796 797 798 799 800 801 802 803 804 805 806 807 808 809 810
 * @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.
	 */
	BUG_ON(page->index != linear_page_index(vma, address));
#endif
}

L
Linus Torvalds 已提交
811 812 813 814 815 816
/**
 * 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
 *
H
Hugh Dickins 已提交
817
 * The caller needs to hold the pte lock, and the page must be locked in
818 819 820
 * the anon_vma case: to serialize mapping,index checking after setting,
 * and to ensure that PageAnon is not being upgraded racily to PageKsm
 * (but PageKsm is never downgraded to PageAnon).
L
Linus Torvalds 已提交
821 822 823 824
 */
void page_add_anon_rmap(struct page *page,
	struct vm_area_struct *vma, unsigned long address)
{
H
Hugh Dickins 已提交
825 826 827 828 829 830
	int first = atomic_inc_and_test(&page->_mapcount);
	if (first)
		__inc_zone_page_state(page, NR_ANON_PAGES);
	if (unlikely(PageKsm(page)))
		return;

N
Nick Piggin 已提交
831 832
	VM_BUG_ON(!PageLocked(page));
	VM_BUG_ON(address < vma->vm_start || address >= vma->vm_end);
H
Hugh Dickins 已提交
833
	if (first)
834
		__page_set_anon_rmap(page, vma, address, 0);
835
	else
N
Nick Piggin 已提交
836
		__page_check_anon_rmap(page, vma, address);
L
Linus Torvalds 已提交
837 838
}

R
Randy Dunlap 已提交
839
/**
N
Nick Piggin 已提交
840 841 842 843 844 845 846
 * 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
847
 * Page does not have to be locked.
N
Nick Piggin 已提交
848 849 850 851
 */
void page_add_new_anon_rmap(struct page *page,
	struct vm_area_struct *vma, unsigned long address)
{
852
	VM_BUG_ON(address < vma->vm_start || address >= vma->vm_end);
853 854
	SetPageSwapBacked(page);
	atomic_set(&page->_mapcount, 0); /* increment count (starts at -1) */
H
Hugh Dickins 已提交
855
	__inc_zone_page_state(page, NR_ANON_PAGES);
856
	__page_set_anon_rmap(page, vma, address, 1);
857
	if (page_evictable(page, vma))
858
		lru_cache_add_lru(page, LRU_ACTIVE_ANON);
859 860
	else
		add_page_to_unevictable_list(page);
N
Nick Piggin 已提交
861 862
}

L
Linus Torvalds 已提交
863 864 865 866
/**
 * page_add_file_rmap - add pte mapping to a file page
 * @page: the page to add the mapping to
 *
867
 * The caller needs to hold the pte lock.
L
Linus Torvalds 已提交
868 869 870
 */
void page_add_file_rmap(struct page *page)
{
871
	if (atomic_inc_and_test(&page->_mapcount)) {
872
		__inc_zone_page_state(page, NR_FILE_MAPPED);
873
		mem_cgroup_update_file_mapped(page, 1);
874
	}
L
Linus Torvalds 已提交
875 876 877 878 879 880
}

/**
 * page_remove_rmap - take down pte mapping from a page
 * @page: page to remove mapping from
 *
881
 * The caller needs to hold the pte lock.
L
Linus Torvalds 已提交
882
 */
883
void page_remove_rmap(struct page *page)
L
Linus Torvalds 已提交
884
{
885 886 887 888 889 890 891 892 893 894 895 896 897 898
	/* page still mapped by someone else? */
	if (!atomic_add_negative(-1, &page->_mapcount))
		return;

	/*
	 * 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.
	 */
	if ((!PageAnon(page) || PageSwapCache(page)) && page_test_dirty(page)) {
		page_clear_dirty(page);
		set_page_dirty(page);
L
Linus Torvalds 已提交
899
	}
900 901 902 903 904
	if (PageAnon(page)) {
		mem_cgroup_uncharge_page(page);
		__dec_zone_page_state(page, NR_ANON_PAGES);
	} else {
		__dec_zone_page_state(page, NR_FILE_MAPPED);
905
		mem_cgroup_update_file_mapped(page, -1);
906 907 908 909 910 911 912 913 914 915
	}
	/*
	 * 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.
	 */
L
Linus Torvalds 已提交
916 917 918 919 920 921
}

/*
 * Subfunctions of try_to_unmap: try_to_unmap_one called
 * repeatedly from either try_to_unmap_anon or try_to_unmap_file.
 */
H
Hugh Dickins 已提交
922 923
int try_to_unmap_one(struct page *page, struct vm_area_struct *vma,
		     unsigned long address, enum ttu_flags flags)
L
Linus Torvalds 已提交
924 925 926 927
{
	struct mm_struct *mm = vma->vm_mm;
	pte_t *pte;
	pte_t pteval;
H
Hugh Dickins 已提交
928
	spinlock_t *ptl;
L
Linus Torvalds 已提交
929 930
	int ret = SWAP_AGAIN;

N
Nick Piggin 已提交
931
	pte = page_check_address(page, mm, address, &ptl, 0);
H
Hugh Dickins 已提交
932
	if (!pte)
N
Nikita Danilov 已提交
933
		goto out;
L
Linus Torvalds 已提交
934 935 936 937 938 939

	/*
	 * 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.
	 */
940
	if (!(flags & TTU_IGNORE_MLOCK)) {
K
KOSAKI Motohiro 已提交
941 942 943
		if (vma->vm_flags & VM_LOCKED)
			goto out_mlock;

H
Hugh Dickins 已提交
944
		if (TTU_ACTION(flags) == TTU_MUNLOCK)
H
Hugh Dickins 已提交
945
			goto out_unmap;
946 947
	}
	if (!(flags & TTU_IGNORE_ACCESS)) {
N
Nick Piggin 已提交
948 949 950 951 952
		if (ptep_clear_flush_young_notify(vma, address, pte)) {
			ret = SWAP_FAIL;
			goto out_unmap;
		}
  	}
L
Linus Torvalds 已提交
953 954 955

	/* Nuke the page table entry. */
	flush_cache_page(vma, address, page_to_pfn(page));
A
Andrea Arcangeli 已提交
956
	pteval = ptep_clear_flush_notify(vma, address, pte);
L
Linus Torvalds 已提交
957 958 959 960 961

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

962 963 964
	/* Update high watermark before we lower rss */
	update_hiwater_rss(mm);

965 966
	if (PageHWPoison(page) && !(flags & TTU_IGNORE_HWPOISON)) {
		if (PageAnon(page))
K
KAMEZAWA Hiroyuki 已提交
967
			dec_mm_counter(mm, MM_ANONPAGES);
968
		else
K
KAMEZAWA Hiroyuki 已提交
969
			dec_mm_counter(mm, MM_FILEPAGES);
970 971 972
		set_pte_at(mm, address, pte,
				swp_entry_to_pte(make_hwpoison_entry(page)));
	} else if (PageAnon(page)) {
H
Hugh Dickins 已提交
973
		swp_entry_t entry = { .val = page_private(page) };
974 975 976 977 978 979

		if (PageSwapCache(page)) {
			/*
			 * Store the swap location in the pte.
			 * See handle_pte_fault() ...
			 */
H
Hugh Dickins 已提交
980 981 982 983 984
			if (swap_duplicate(entry) < 0) {
				set_pte_at(mm, address, pte, pteval);
				ret = SWAP_FAIL;
				goto out_unmap;
			}
985 986 987 988 989 990
			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);
			}
K
KAMEZAWA Hiroyuki 已提交
991
			dec_mm_counter(mm, MM_ANONPAGES);
K
KAMEZAWA Hiroyuki 已提交
992
			inc_mm_counter(mm, MM_SWAPENTS);
993
		} else if (PAGE_MIGRATION) {
994 995 996 997 998
			/*
			 * 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.
			 */
999
			BUG_ON(TTU_ACTION(flags) != TTU_MIGRATION);
1000
			entry = make_migration_entry(page, pte_write(pteval));
L
Linus Torvalds 已提交
1001 1002 1003
		}
		set_pte_at(mm, address, pte, swp_entry_to_pte(entry));
		BUG_ON(pte_file(*pte));
1004
	} else if (PAGE_MIGRATION && (TTU_ACTION(flags) == TTU_MIGRATION)) {
1005 1006 1007 1008 1009
		/* 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
K
KAMEZAWA Hiroyuki 已提交
1010
		dec_mm_counter(mm, MM_FILEPAGES);
L
Linus Torvalds 已提交
1011

1012
	page_remove_rmap(page);
L
Linus Torvalds 已提交
1013 1014 1015
	page_cache_release(page);

out_unmap:
H
Hugh Dickins 已提交
1016
	pte_unmap_unlock(pte, ptl);
K
KOSAKI Motohiro 已提交
1017 1018
out:
	return ret;
H
Hugh Dickins 已提交
1019

K
KOSAKI Motohiro 已提交
1020 1021 1022 1023 1024 1025 1026 1027 1028 1029 1030 1031 1032 1033 1034 1035
out_mlock:
	pte_unmap_unlock(pte, ptl);


	/*
	 * We need mmap_sem locking, Otherwise VM_LOCKED check makes
	 * unstable result and race. Plus, We can't wait here because
	 * we now hold anon_vma->lock or mapping->i_mmap_lock.
	 * if trylock failed, the page remain in evictable lru and later
	 * vmscan could retry to move the page to unevictable lru if the
	 * page is actually mlocked.
	 */
	if (down_read_trylock(&vma->vm_mm->mmap_sem)) {
		if (vma->vm_flags & VM_LOCKED) {
			mlock_vma_page(page);
			ret = SWAP_MLOCK;
H
Hugh Dickins 已提交
1036
		}
K
KOSAKI Motohiro 已提交
1037
		up_read(&vma->vm_mm->mmap_sem);
H
Hugh Dickins 已提交
1038
	}
L
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1039 1040 1041 1042 1043 1044 1045 1046 1047 1048 1049 1050 1051 1052 1053 1054 1055 1056 1057 1058 1059
	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
1060 1061 1062 1063 1064
 *
 * 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
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 */
#define CLUSTER_SIZE	min(32*PAGE_SIZE, PMD_SIZE)
#define CLUSTER_MASK	(~(CLUSTER_SIZE - 1))

N
Nick Piggin 已提交
1069 1070
static int try_to_unmap_cluster(unsigned long cursor, unsigned int *mapcount,
		struct vm_area_struct *vma, struct page *check_page)
L
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1071 1072 1073 1074 1075
{
	struct mm_struct *mm = vma->vm_mm;
	pgd_t *pgd;
	pud_t *pud;
	pmd_t *pmd;
H
Hugh Dickins 已提交
1076
	pte_t *pte;
L
Linus Torvalds 已提交
1077
	pte_t pteval;
H
Hugh Dickins 已提交
1078
	spinlock_t *ptl;
L
Linus Torvalds 已提交
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	struct page *page;
	unsigned long address;
	unsigned long end;
N
Nick Piggin 已提交
1082 1083
	int ret = SWAP_AGAIN;
	int locked_vma = 0;
L
Linus Torvalds 已提交
1084 1085 1086 1087 1088 1089 1090 1091 1092 1093

	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
1094
		return ret;
L
Linus Torvalds 已提交
1095 1096 1097

	pud = pud_offset(pgd, address);
	if (!pud_present(*pud))
N
Nick Piggin 已提交
1098
		return ret;
L
Linus Torvalds 已提交
1099 1100 1101

	pmd = pmd_offset(pud, address);
	if (!pmd_present(*pmd))
N
Nick Piggin 已提交
1102 1103 1104
		return ret;

	/*
H
Hugh Dickins 已提交
1105
	 * If we can acquire the mmap_sem for read, and vma is VM_LOCKED,
N
Nick Piggin 已提交
1106 1107
	 * keep the sem while scanning the cluster for mlocking pages.
	 */
H
Hugh Dickins 已提交
1108
	if (down_read_trylock(&vma->vm_mm->mmap_sem)) {
N
Nick Piggin 已提交
1109 1110 1111 1112
		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
1113 1114

	pte = pte_offset_map_lock(mm, pmd, address, &ptl);
L
Linus Torvalds 已提交
1115

1116 1117 1118
	/* Update high watermark before we lower rss */
	update_hiwater_rss(mm);

H
Hugh Dickins 已提交
1119
	for (; address < end; pte++, address += PAGE_SIZE) {
L
Linus Torvalds 已提交
1120 1121
		if (!pte_present(*pte))
			continue;
1122 1123
		page = vm_normal_page(vma, address, *pte);
		BUG_ON(!page || PageAnon(page));
L
Linus Torvalds 已提交
1124

N
Nick Piggin 已提交
1125 1126 1127 1128 1129 1130 1131
		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
1132
		if (ptep_clear_flush_young_notify(vma, address, pte))
L
Linus Torvalds 已提交
1133 1134 1135
			continue;

		/* Nuke the page table entry. */
1136
		flush_cache_page(vma, address, pte_pfn(*pte));
A
Andrea Arcangeli 已提交
1137
		pteval = ptep_clear_flush_notify(vma, address, pte);
L
Linus Torvalds 已提交
1138 1139 1140 1141 1142 1143 1144 1145 1146

		/* 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);

1147
		page_remove_rmap(page);
L
Linus Torvalds 已提交
1148
		page_cache_release(page);
K
KAMEZAWA Hiroyuki 已提交
1149
		dec_mm_counter(mm, MM_FILEPAGES);
L
Linus Torvalds 已提交
1150 1151
		(*mapcount)--;
	}
H
Hugh Dickins 已提交
1152
	pte_unmap_unlock(pte - 1, ptl);
N
Nick Piggin 已提交
1153 1154 1155
	if (locked_vma)
		up_read(&vma->vm_mm->mmap_sem);
	return ret;
L
Linus Torvalds 已提交
1156 1157
}

1158 1159 1160 1161 1162 1163 1164 1165 1166 1167 1168 1169 1170 1171
static bool is_vma_temporary_stack(struct vm_area_struct *vma)
{
	int maybe_stack = vma->vm_flags & (VM_GROWSDOWN | VM_GROWSUP);

	if (!maybe_stack)
		return false;

	if ((vma->vm_flags & VM_STACK_INCOMPLETE_SETUP) ==
						VM_STACK_INCOMPLETE_SETUP)
		return true;

	return false;
}

N
Nick Piggin 已提交
1172 1173 1174 1175
/**
 * try_to_unmap_anon - unmap or unlock anonymous page using the object-based
 * rmap method
 * @page: the page to unmap/unlock
1176
 * @flags: action and flags
N
Nick Piggin 已提交
1177 1178 1179 1180 1181 1182 1183 1184 1185 1186 1187
 *
 * 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.
 */
1188
static int try_to_unmap_anon(struct page *page, enum ttu_flags flags)
L
Linus Torvalds 已提交
1189 1190
{
	struct anon_vma *anon_vma;
1191
	struct anon_vma_chain *avc;
L
Linus Torvalds 已提交
1192
	int ret = SWAP_AGAIN;
N
Nick Piggin 已提交
1193

L
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1194 1195 1196 1197
	anon_vma = page_lock_anon_vma(page);
	if (!anon_vma)
		return ret;

1198 1199
	list_for_each_entry(avc, &anon_vma->head, same_anon_vma) {
		struct vm_area_struct *vma = avc->vma;
1200 1201 1202 1203 1204 1205 1206 1207 1208 1209 1210 1211 1212 1213 1214
		unsigned long address;

		/*
		 * During exec, a temporary VMA is setup and later moved.
		 * The VMA is moved under the anon_vma lock but not the
		 * page tables leading to a race where migration cannot
		 * find the migration ptes. Rather than increasing the
		 * locking requirements of exec(), migration skips
		 * temporary VMAs until after exec() completes.
		 */
		if (PAGE_MIGRATION && (flags & TTU_MIGRATION) &&
				is_vma_temporary_stack(vma))
			continue;

		address = vma_address(page, vma);
H
Hugh Dickins 已提交
1215 1216 1217
		if (address == -EFAULT)
			continue;
		ret = try_to_unmap_one(page, vma, address, flags);
H
Hugh Dickins 已提交
1218 1219
		if (ret != SWAP_AGAIN || !page_mapped(page))
			break;
L
Linus Torvalds 已提交
1220
	}
1221 1222

	page_unlock_anon_vma(anon_vma);
L
Linus Torvalds 已提交
1223 1224 1225 1226
	return ret;
}

/**
N
Nick Piggin 已提交
1227 1228
 * try_to_unmap_file - unmap/unlock file page using the object-based rmap method
 * @page: the page to unmap/unlock
1229
 * @flags: action and flags
L
Linus Torvalds 已提交
1230 1231 1232 1233
 *
 * 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
1234 1235 1236 1237 1238 1239
 * 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
1240
 */
1241
static int try_to_unmap_file(struct page *page, enum ttu_flags flags)
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1242 1243 1244 1245 1246 1247 1248 1249 1250 1251 1252 1253 1254
{
	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;

	spin_lock(&mapping->i_mmap_lock);
	vma_prio_tree_foreach(vma, &iter, &mapping->i_mmap, pgoff, pgoff) {
H
Hugh Dickins 已提交
1255 1256 1257 1258
		unsigned long address = vma_address(page, vma);
		if (address == -EFAULT)
			continue;
		ret = try_to_unmap_one(page, vma, address, flags);
H
Hugh Dickins 已提交
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		if (ret != SWAP_AGAIN || !page_mapped(page))
			goto out;
L
Linus Torvalds 已提交
1261 1262 1263 1264 1265
	}

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

H
Hugh Dickins 已提交
1266 1267 1268 1269 1270 1271 1272 1273
	/*
	 * We don't bother to try to find the munlocked page in nonlinears.
	 * It's costly. Instead, later, page reclaim logic may call
	 * try_to_unmap(TTU_MUNLOCK) and recover PG_mlocked lazily.
	 */
	if (TTU_ACTION(flags) == TTU_MUNLOCK)
		goto out;

L
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1274 1275 1276 1277 1278 1279 1280 1281 1282 1283
	list_for_each_entry(vma, &mapping->i_mmap_nonlinear,
						shared.vm_set.list) {
		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;
	}

N
Nick Piggin 已提交
1284
	if (max_nl_size == 0) {	/* all nonlinears locked or reserved ? */
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1285 1286 1287 1288 1289 1290 1291 1292 1293 1294 1295 1296 1297 1298 1299 1300 1301 1302 1303 1304 1305 1306 1307 1308
		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) {
			cursor = (unsigned long) vma->vm_private_data;
H
Hugh Dickins 已提交
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			while ( cursor < max_nl_cursor &&
L
Linus Torvalds 已提交
1310
				cursor < vma->vm_end - vma->vm_start) {
H
Hugh Dickins 已提交
1311 1312 1313
				if (try_to_unmap_cluster(cursor, &mapcount,
						vma, page) == SWAP_MLOCK)
					ret = SWAP_MLOCK;
L
Linus Torvalds 已提交
1314 1315 1316 1317 1318 1319 1320 1321 1322 1323 1324 1325 1326 1327 1328 1329
				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.
	 */
1330 1331
	list_for_each_entry(vma, &mapping->i_mmap_nonlinear, shared.vm_set.list)
		vma->vm_private_data = NULL;
L
Linus Torvalds 已提交
1332 1333 1334 1335 1336 1337 1338 1339
out:
	spin_unlock(&mapping->i_mmap_lock);
	return ret;
}

/**
 * try_to_unmap - try to remove all page table mappings to a page
 * @page: the page to get unmapped
1340
 * @flags: action and flags
L
Linus Torvalds 已提交
1341 1342 1343 1344 1345 1346 1347 1348
 *
 * 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
N
Nick Piggin 已提交
1349
 * SWAP_MLOCK	- page is mlocked.
L
Linus Torvalds 已提交
1350
 */
1351
int try_to_unmap(struct page *page, enum ttu_flags flags)
L
Linus Torvalds 已提交
1352 1353 1354 1355 1356
{
	int ret;

	BUG_ON(!PageLocked(page));

H
Hugh Dickins 已提交
1357 1358 1359
	if (unlikely(PageKsm(page)))
		ret = try_to_unmap_ksm(page, flags);
	else if (PageAnon(page))
1360
		ret = try_to_unmap_anon(page, flags);
L
Linus Torvalds 已提交
1361
	else
1362
		ret = try_to_unmap_file(page, flags);
N
Nick Piggin 已提交
1363
	if (ret != SWAP_MLOCK && !page_mapped(page))
L
Linus Torvalds 已提交
1364 1365 1366
		ret = SWAP_SUCCESS;
	return ret;
}
N
Nikita Danilov 已提交
1367

N
Nick Piggin 已提交
1368 1369 1370 1371 1372 1373 1374 1375 1376 1377
/**
 * 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:
 *
H
Hugh Dickins 已提交
1378
 * SWAP_AGAIN	- no vma is holding page mlocked, or,
N
Nick Piggin 已提交
1379
 * SWAP_AGAIN	- page mapped in mlocked vma -- couldn't acquire mmap sem
H
Hugh Dickins 已提交
1380
 * SWAP_FAIL	- page cannot be located at present
N
Nick Piggin 已提交
1381 1382 1383 1384 1385 1386
 * SWAP_MLOCK	- page is now mlocked.
 */
int try_to_munlock(struct page *page)
{
	VM_BUG_ON(!PageLocked(page) || PageLRU(page));

H
Hugh Dickins 已提交
1387 1388 1389
	if (unlikely(PageKsm(page)))
		return try_to_unmap_ksm(page, TTU_MUNLOCK);
	else if (PageAnon(page))
1390
		return try_to_unmap_anon(page, TTU_MUNLOCK);
N
Nick Piggin 已提交
1391
	else
1392
		return try_to_unmap_file(page, TTU_MUNLOCK);
N
Nick Piggin 已提交
1393
}
1394

1395 1396 1397 1398 1399 1400 1401 1402 1403 1404 1405 1406 1407 1408 1409 1410 1411 1412 1413 1414 1415 1416 1417 1418 1419 1420 1421 1422 1423 1424 1425 1426 1427 1428
#if defined(CONFIG_KSM) || defined(CONFIG_MIGRATION)
/*
 * Drop an anon_vma refcount, freeing the anon_vma and anon_vma->root
 * if necessary.  Be careful to do all the tests under the lock.  Once
 * we know we are the last user, nobody else can get a reference and we
 * can do the freeing without the lock.
 */
void drop_anon_vma(struct anon_vma *anon_vma)
{
	if (atomic_dec_and_lock(&anon_vma->external_refcount, &anon_vma->root->lock)) {
		struct anon_vma *root = anon_vma->root;
		int empty = list_empty(&anon_vma->head);
		int last_root_user = 0;
		int root_empty = 0;

		/*
		 * The refcount on a non-root anon_vma got dropped.  Drop
		 * the refcount on the root and check if we need to free it.
		 */
		if (empty && anon_vma != root) {
			last_root_user = atomic_dec_and_test(&root->external_refcount);
			root_empty = list_empty(&root->head);
		}
		anon_vma_unlock(anon_vma);

		if (empty) {
			anon_vma_free(anon_vma);
			if (root_empty && last_root_user)
				anon_vma_free(root);
		}
	}
}
#endif

1429 1430 1431 1432 1433 1434 1435 1436 1437
#ifdef CONFIG_MIGRATION
/*
 * rmap_walk() and its helpers rmap_walk_anon() and rmap_walk_file():
 * Called by migrate.c to remove migration ptes, but might be used more later.
 */
static int rmap_walk_anon(struct page *page, int (*rmap_one)(struct page *,
		struct vm_area_struct *, unsigned long, void *), void *arg)
{
	struct anon_vma *anon_vma;
1438
	struct anon_vma_chain *avc;
1439 1440 1441 1442 1443
	int ret = SWAP_AGAIN;

	/*
	 * Note: remove_migration_ptes() cannot use page_lock_anon_vma()
	 * because that depends on page_mapped(); but not all its usages
1444 1445
	 * are holding mmap_sem. Users without mmap_sem are required to
	 * take a reference count to prevent the anon_vma disappearing
1446 1447 1448 1449
	 */
	anon_vma = page_anon_vma(page);
	if (!anon_vma)
		return ret;
1450
	anon_vma_lock(anon_vma);
1451 1452
	list_for_each_entry(avc, &anon_vma->head, same_anon_vma) {
		struct vm_area_struct *vma = avc->vma;
1453 1454 1455 1456 1457 1458 1459
		unsigned long address = vma_address(page, vma);
		if (address == -EFAULT)
			continue;
		ret = rmap_one(page, vma, address, arg);
		if (ret != SWAP_AGAIN)
			break;
	}
1460
	anon_vma_unlock(anon_vma);
1461 1462 1463 1464 1465 1466 1467 1468 1469 1470 1471 1472 1473 1474 1475 1476 1477 1478 1479 1480 1481 1482 1483 1484 1485 1486 1487 1488 1489 1490 1491 1492 1493 1494 1495 1496 1497 1498 1499 1500 1501 1502 1503 1504 1505
	return ret;
}

static int rmap_walk_file(struct page *page, int (*rmap_one)(struct page *,
		struct vm_area_struct *, unsigned long, void *), void *arg)
{
	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;

	if (!mapping)
		return ret;
	spin_lock(&mapping->i_mmap_lock);
	vma_prio_tree_foreach(vma, &iter, &mapping->i_mmap, pgoff, pgoff) {
		unsigned long address = vma_address(page, vma);
		if (address == -EFAULT)
			continue;
		ret = rmap_one(page, vma, address, arg);
		if (ret != SWAP_AGAIN)
			break;
	}
	/*
	 * No nonlinear handling: being always shared, nonlinear vmas
	 * never contain migration ptes.  Decide what to do about this
	 * limitation to linear when we need rmap_walk() on nonlinear.
	 */
	spin_unlock(&mapping->i_mmap_lock);
	return ret;
}

int rmap_walk(struct page *page, int (*rmap_one)(struct page *,
		struct vm_area_struct *, unsigned long, void *), void *arg)
{
	VM_BUG_ON(!PageLocked(page));

	if (unlikely(PageKsm(page)))
		return rmap_walk_ksm(page, rmap_one, arg);
	else if (PageAnon(page))
		return rmap_walk_anon(page, rmap_one, arg);
	else
		return rmap_walk_file(page, rmap_one, arg);
}
#endif /* CONFIG_MIGRATION */