linux/mm/rmap.c

1230 lines
34 KiB
C

/*
* 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 2003, 2004
*/
/*
* Lock ordering in mm:
*
* inode->i_mutex (while writing or truncating, not reading or faulting)
* 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)
*/
#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>
#include <linux/module.h>
#include <linux/memcontrol.h>
#include <linux/mmu_notifier.h>
#include <linux/migrate.h>
#include <asm/tlbflush.h>
#include "internal.h"
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);
}
/**
* 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.
*/
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;
struct anon_vma *allocated;
anon_vma = find_mergeable_anon_vma(vma);
allocated = NULL;
if (!anon_vma) {
anon_vma = anon_vma_alloc();
if (unlikely(!anon_vma))
return -ENOMEM;
allocated = anon_vma;
}
spin_lock(&anon_vma->lock);
/* page_table_lock to protect against threads */
spin_lock(&mm->page_table_lock);
if (likely(!vma->anon_vma)) {
vma->anon_vma = anon_vma;
list_add_tail(&vma->anon_vma_node, &anon_vma->head);
allocated = NULL;
}
spin_unlock(&mm->page_table_lock);
spin_unlock(&anon_vma->lock);
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;
if (anon_vma)
list_add_tail(&vma->anon_vma_node, &anon_vma->head);
}
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);
list_add_tail(&vma->anon_vma_node, &anon_vma->head);
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);
}
static void anon_vma_ctor(void *data)
{
struct anon_vma *anon_vma = data;
spin_lock_init(&anon_vma->lock);
INIT_LIST_HEAD(&anon_vma->head);
}
void __init anon_vma_init(void)
{
anon_vma_cachep = kmem_cache_create("anon_vma", sizeof(struct anon_vma),
0, SLAB_DESTROY_BY_RCU|SLAB_PANIC, anon_vma_ctor);
}
/*
* 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.
*/
static struct anon_vma *page_lock_anon_vma(struct page *page)
{
struct anon_vma *anon_vma;
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);
return anon_vma;
out:
rcu_read_unlock();
return NULL;
}
static void page_unlock_anon_vma(struct anon_vma *anon_vma)
{
spin_unlock(&anon_vma->lock);
rcu_read_unlock();
}
/*
* 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.
*/
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)) {
/* page should be within @vma mapping range */
return -EFAULT;
}
return address;
}
/*
* At what user virtual address is page expected in vma? checking that the
* page matches the vma: currently only used on anon pages, by unuse_vma;
*/
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)) {
if (!vma->vm_file ||
vma->vm_file->f_mapping != page->mapping)
return -EFAULT;
} else
return -EFAULT;
return vma_address(page, vma);
}
/*
* Check that @page is mapped at @address into @mm.
*
* 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).
*
* On success returns with pte mapped and locked.
*/
pte_t *page_check_address(struct page *page, struct mm_struct *mm,
unsigned long address, spinlock_t **ptlp, int sync)
{
pgd_t *pgd;
pud_t *pud;
pmd_t *pmd;
pte_t *pte;
spinlock_t *ptl;
pgd = pgd_offset(mm, address);
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 */
if (!sync && !pte_present(*pte)) {
pte_unmap(pte);
return NULL;
}
ptl = pte_lockptr(mm, pmd);
spin_lock(ptl);
if (pte_present(*pte) && page_to_pfn(page) == pte_pfn(*pte)) {
*ptlp = ptl;
return pte;
}
pte_unmap_unlock(pte, ptl);
return NULL;
}
/**
* 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;
}
/*
* 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,
struct vm_area_struct *vma,
unsigned int *mapcount,
unsigned long *vm_flags)
{
struct mm_struct *mm = vma->vm_mm;
unsigned long address;
pte_t *pte;
spinlock_t *ptl;
int referenced = 0;
address = vma_address(page, vma);
if (address == -EFAULT)
goto out;
pte = page_check_address(page, mm, address, &ptl, 0);
if (!pte)
goto out;
/*
* 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.
*/
if (vma->vm_flags & VM_LOCKED) {
*mapcount = 1; /* break early from loop */
*vm_flags |= VM_LOCKED;
goto out_unmap;
}
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++;
}
/* Pretend the page is referenced if the task has the
swap token and is in the middle of a page fault. */
if (mm != current->mm && has_swap_token(mm) &&
rwsem_is_locked(&mm->mmap_sem))
referenced++;
out_unmap:
(*mapcount)--;
pte_unmap_unlock(pte, ptl);
out:
if (referenced)
*vm_flags |= vma->vm_flags;
return referenced;
}
static int page_referenced_anon(struct page *page,
struct mem_cgroup *mem_cont,
unsigned long *vm_flags)
{
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) {
/*
* If we are reclaiming on behalf of a cgroup, skip
* counting on behalf of references from different
* cgroups
*/
if (mem_cont && !mm_match_cgroup(vma->vm_mm, mem_cont))
continue;
referenced += page_referenced_one(page, vma,
&mapcount, vm_flags);
if (!mapcount)
break;
}
page_unlock_anon_vma(anon_vma);
return referenced;
}
/**
* page_referenced_file - referenced check for object-based rmap
* @page: the page we're checking references on.
* @mem_cont: target memory controller
* @vm_flags: collect encountered vma->vm_flags who actually referenced the page
*
* 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.
*/
static int page_referenced_file(struct page *page,
struct mem_cgroup *mem_cont,
unsigned long *vm_flags)
{
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) {
/*
* If we are reclaiming on behalf of a cgroup, skip
* counting on behalf of references from different
* cgroups
*/
if (mem_cont && !mm_match_cgroup(vma->vm_mm, mem_cont))
continue;
referenced += page_referenced_one(page, vma,
&mapcount, vm_flags);
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
* @mem_cont: target memory controller
* @vm_flags: collect encountered vma->vm_flags who actually referenced the page
*
* Quick test_and_clear_referenced for all mappings to a page,
* returns the number of ptes which referenced the page.
*/
int page_referenced(struct page *page,
int is_locked,
struct mem_cgroup *mem_cont,
unsigned long *vm_flags)
{
int referenced = 0;
if (TestClearPageReferenced(page))
referenced++;
*vm_flags = 0;
if (page_mapped(page) && page->mapping) {
if (PageAnon(page))
referenced += page_referenced_anon(page, mem_cont,
vm_flags);
else if (is_locked)
referenced += page_referenced_file(page, mem_cont,
vm_flags);
else if (!trylock_page(page))
referenced++;
else {
if (page->mapping)
referenced += page_referenced_file(page,
mem_cont, vm_flags);
unlock_page(page);
}
}
if (page_test_and_clear_young(page))
referenced++;
return referenced;
}
static int page_mkclean_one(struct page *page, struct vm_area_struct *vma)
{
struct mm_struct *mm = vma->vm_mm;
unsigned long address;
pte_t *pte;
spinlock_t *ptl;
int ret = 0;
address = vma_address(page, vma);
if (address == -EFAULT)
goto out;
pte = page_check_address(page, mm, address, &ptl, 1);
if (!pte)
goto out;
if (pte_dirty(*pte) || pte_write(*pte)) {
pte_t entry;
flush_cache_page(vma, address, pte_pfn(*pte));
entry = ptep_clear_flush_notify(vma, address, pte);
entry = pte_wrprotect(entry);
entry = pte_mkclean(entry);
set_pte_at(mm, address, pte, entry);
ret = 1;
}
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);
if (mapping) {
ret = page_mkclean_file(mapping, page);
if (page_test_dirty(page)) {
page_clear_dirty(page);
ret = 1;
}
}
}
return ret;
}
EXPORT_SYMBOL_GPL(page_mkclean);
/**
* __page_set_anon_rmap - setup new anonymous rmap
* @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);
/*
* nr_mapped state can be updated without turning off
* interrupts because it is not modified via interrupt.
*/
__inc_zone_page_state(page, NR_ANON_PAGES);
}
/**
* __page_check_anon_rmap - sanity check anonymous rmap addition
* @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
}
/**
* 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
*
* The caller needs to hold the pte lock and the page must be locked.
*/
void page_add_anon_rmap(struct page *page,
struct vm_area_struct *vma, unsigned long address)
{
VM_BUG_ON(!PageLocked(page));
VM_BUG_ON(address < vma->vm_start || address >= vma->vm_end);
if (atomic_inc_and_test(&page->_mapcount))
__page_set_anon_rmap(page, vma, address);
else
__page_check_anon_rmap(page, vma, address);
}
/**
* 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.
* Page does not have to be locked.
*/
void page_add_new_anon_rmap(struct page *page,
struct vm_area_struct *vma, unsigned long address)
{
VM_BUG_ON(address < vma->vm_start || address >= vma->vm_end);
SetPageSwapBacked(page);
atomic_set(&page->_mapcount, 0); /* increment count (starts at -1) */
__page_set_anon_rmap(page, vma, address);
if (page_evictable(page, vma))
lru_cache_add_lru(page, LRU_ACTIVE_ANON);
else
add_page_to_unevictable_list(page);
}
/**
* page_add_file_rmap - add pte mapping to a file page
* @page: the page to add the mapping to
*
* The caller needs to hold the pte lock.
*/
void page_add_file_rmap(struct page *page)
{
if (atomic_inc_and_test(&page->_mapcount)) {
__inc_zone_page_state(page, NR_FILE_MAPPED);
mem_cgroup_update_mapped_file_stat(page, 1);
}
}
/**
* page_remove_rmap - take down pte mapping from a page
* @page: page to remove mapping from
*
* The caller needs to hold the pte lock.
*/
void page_remove_rmap(struct page *page)
{
/* 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);
}
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);
}
mem_cgroup_update_mapped_file_stat(page, -1);
/*
* 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.
*/
}
/*
* Subfunctions of try_to_unmap: try_to_unmap_one called
* repeatedly from either try_to_unmap_anon or try_to_unmap_file.
*/
static int try_to_unmap_one(struct page *page, struct vm_area_struct *vma,
int migration)
{
struct mm_struct *mm = vma->vm_mm;
unsigned long address;
pte_t *pte;
pte_t pteval;
spinlock_t *ptl;
int ret = SWAP_AGAIN;
address = vma_address(page, vma);
if (address == -EFAULT)
goto out;
pte = page_check_address(page, mm, address, &ptl, 0);
if (!pte)
goto out;
/*
* 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.
*/
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;
}
}
/* Nuke the page table entry. */
flush_cache_page(vma, address, page_to_pfn(page));
pteval = ptep_clear_flush_notify(vma, address, pte);
/* Move the dirty bit to the physical page now the pte is gone. */
if (pte_dirty(pteval))
set_page_dirty(page);
/* Update high watermark before we lower rss */
update_hiwater_rss(mm);
if (PageAnon(page)) {
swp_entry_t entry = { .val = page_private(page) };
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);
}
dec_mm_counter(mm, anon_rss);
} else if (PAGE_MIGRATION) {
/*
* 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));
}
set_pte_at(mm, address, pte, swp_entry_to_pte(entry));
BUG_ON(pte_file(*pte));
} else if (PAGE_MIGRATION && migration) {
/* 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
dec_mm_counter(mm, file_rss);
page_remove_rmap(page);
page_cache_release(page);
out_unmap:
pte_unmap_unlock(pte, ptl);
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.
*
* 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.
*/
#define CLUSTER_SIZE min(32*PAGE_SIZE, PMD_SIZE)
#define CLUSTER_MASK (~(CLUSTER_SIZE - 1))
static int try_to_unmap_cluster(unsigned long cursor, unsigned int *mapcount,
struct vm_area_struct *vma, struct page *check_page)
{
struct mm_struct *mm = vma->vm_mm;
pgd_t *pgd;
pud_t *pud;
pmd_t *pmd;
pte_t *pte;
pte_t pteval;
spinlock_t *ptl;
struct page *page;
unsigned long address;
unsigned long end;
int ret = SWAP_AGAIN;
int locked_vma = 0;
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))
return ret;
pud = pud_offset(pgd, address);
if (!pud_present(*pud))
return ret;
pmd = pmd_offset(pud, address);
if (!pmd_present(*pmd))
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 */
}
pte = pte_offset_map_lock(mm, pmd, address, &ptl);
/* Update high watermark before we lower rss */
update_hiwater_rss(mm);
for (; address < end; pte++, address += PAGE_SIZE) {
if (!pte_present(*pte))
continue;
page = vm_normal_page(vma, address, *pte);
BUG_ON(!page || PageAnon(page));
if (locked_vma) {
mlock_vma_page(page); /* no-op if already mlocked */
if (page == check_page)
ret = SWAP_MLOCK;
continue; /* don't unmap */
}
if (ptep_clear_flush_young_notify(vma, address, pte))
continue;
/* Nuke the page table entry. */
flush_cache_page(vma, address, pte_pfn(*pte));
pteval = ptep_clear_flush_notify(vma, address, pte);
/* 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);
page_remove_rmap(page);
page_cache_release(page);
dec_mm_counter(mm, file_rss);
(*mapcount)--;
}
pte_unmap_unlock(pte - 1, ptl);
if (locked_vma)
up_read(&vma->vm_mm->mmap_sem);
return ret;
}
/*
* 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)
{
struct anon_vma *anon_vma;
struct vm_area_struct *vma;
unsigned int mlocked = 0;
int ret = SWAP_AGAIN;
if (MLOCK_PAGES && unlikely(unlock))
ret = SWAP_SUCCESS; /* default for try_to_munlock() */
anon_vma = page_lock_anon_vma(page);
if (!anon_vma)
return ret;
list_for_each_entry(vma, &anon_vma->head, anon_vma_node) {
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 */
}
}
page_unlock_anon_vma(anon_vma);
if (mlocked)
ret = SWAP_MLOCK; /* actually mlocked the page */
else if (ret == SWAP_MLOCK)
ret = SWAP_AGAIN; /* saw VM_LOCKED vma */
return ret;
}
/**
* 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
*
* Find all the mappings of a page using the mapping pointer and the vma chains
* contained in the address_space struct it points to.
*
* 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.
*/
static int try_to_unmap_file(struct page *page, int unlock, int migration)
{
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;
unsigned int mlocked = 0;
if (MLOCK_PAGES && unlikely(unlock))
ret = SWAP_SUCCESS; /* default for try_to_munlock() */
spin_lock(&mapping->i_mmap_lock);
vma_prio_tree_foreach(vma, &iter, &mapping->i_mmap, pgoff, pgoff) {
if (MLOCK_PAGES && unlikely(unlock)) {
if (!((vma->vm_flags & VM_LOCKED) &&
page_mapped_in_vma(page, vma)))
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 */
}
}
if (mlocked)
goto out;
if (list_empty(&mapping->i_mmap_nonlinear))
goto out;
list_for_each_entry(vma, &mapping->i_mmap_nonlinear,
shared.vm_set.list) {
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))
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;
}
if (max_nl_size == 0) { /* all nonlinears locked or reserved ? */
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) {
if (!MLOCK_PAGES && !migration &&
(vma->vm_flags & VM_LOCKED))
continue;
cursor = (unsigned long) vma->vm_private_data;
while ( cursor < max_nl_cursor &&
cursor < vma->vm_end - vma->vm_start) {
ret = try_to_unmap_cluster(cursor, &mapcount,
vma, page);
if (ret == SWAP_MLOCK)
mlocked = 2; /* to return below */
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.
*/
list_for_each_entry(vma, &mapping->i_mmap_nonlinear, shared.vm_set.list)
vma->vm_private_data = NULL;
out:
spin_unlock(&mapping->i_mmap_lock);
if (mlocked)
ret = SWAP_MLOCK; /* actually mlocked the page */
else if (ret == SWAP_MLOCK)
ret = SWAP_AGAIN; /* saw VM_LOCKED vma */
return ret;
}
/**
* try_to_unmap - try to remove all page table mappings to a page
* @page: the page to get unmapped
* @migration: migration flag
*
* 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
* SWAP_MLOCK - page is mlocked.
*/
int try_to_unmap(struct page *page, int migration)
{
int ret;
BUG_ON(!PageLocked(page));
if (PageAnon(page))
ret = try_to_unmap_anon(page, 0, migration);
else
ret = try_to_unmap_file(page, 0, migration);
if (ret != SWAP_MLOCK && !page_mapped(page))
ret = SWAP_SUCCESS;
return ret;
}
/**
* 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);
}