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swapfile.c
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swapfile.c
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/*
* linux/mm/swapfile.c
*
* Copyright (C) 1991, 1992, 1993, 1994 Linus Torvalds
* Swap reorganised 29.12.95, Stephen Tweedie
*/
#include <linux/mm.h>
#include <linux/hugetlb.h>
#include <linux/mman.h>
#include <linux/slab.h>
#include <linux/kernel_stat.h>
#include <linux/swap.h>
#include <linux/vmalloc.h>
#include <linux/pagemap.h>
#include <linux/namei.h>
#include <linux/shm.h>
#include <linux/blkdev.h>
#include <linux/random.h>
#include <linux/writeback.h>
#include <linux/proc_fs.h>
#include <linux/seq_file.h>
#include <linux/init.h>
#include <linux/module.h>
#include <linux/ksm.h>
#include <linux/rmap.h>
#include <linux/security.h>
#include <linux/backing-dev.h>
#include <linux/mutex.h>
#include <linux/capability.h>
#include <linux/syscalls.h>
#include <linux/memcontrol.h>
#include <linux/poll.h>
#include <asm/pgtable.h>
#include <asm/tlbflush.h>
#include <linux/swapops.h>
#include <linux/page_cgroup.h>
static bool swap_count_continued(struct swap_info_struct *, pgoff_t,
unsigned char);
static void free_swap_count_continuations(struct swap_info_struct *);
static sector_t map_swap_entry(swp_entry_t, struct block_device**);
static DEFINE_SPINLOCK(swap_lock);
static unsigned int nr_swapfiles;
long nr_swap_pages;
long total_swap_pages;
static int least_priority;
static const char Bad_file[] = "Bad swap file entry ";
static const char Unused_file[] = "Unused swap file entry ";
static const char Bad_offset[] = "Bad swap offset entry ";
static const char Unused_offset[] = "Unused swap offset entry ";
static struct swap_list_t swap_list = {-1, -1};
static struct swap_info_struct *swap_info[MAX_SWAPFILES];
static DEFINE_MUTEX(swapon_mutex);
static DECLARE_WAIT_QUEUE_HEAD(proc_poll_wait);
/* Activity counter to indicate that a swapon or swapoff has occurred */
static atomic_t proc_poll_event = ATOMIC_INIT(0);
static inline unsigned char swap_count(unsigned char ent)
{
return ent & ~SWAP_HAS_CACHE; /* may include SWAP_HAS_CONT flag */
}
/* returns 1 if swap entry is freed */
static int
__try_to_reclaim_swap(struct swap_info_struct *si, unsigned long offset)
{
swp_entry_t entry = swp_entry(si->type, offset);
struct page *page;
int ret = 0;
page = find_get_page(&swapper_space, entry.val);
if (!page)
return 0;
/*
* This function is called from scan_swap_map() and it's called
* by vmscan.c at reclaiming pages. So, we hold a lock on a page, here.
* We have to use trylock for avoiding deadlock. This is a special
* case and you should use try_to_free_swap() with explicit lock_page()
* in usual operations.
*/
if (trylock_page(page)) {
ret = try_to_free_swap(page);
unlock_page(page);
}
page_cache_release(page);
return ret;
}
/*
* We need this because the bdev->unplug_fn can sleep and we cannot
* hold swap_lock while calling the unplug_fn. And swap_lock
* cannot be turned into a mutex.
*/
static DECLARE_RWSEM(swap_unplug_sem);
void swap_unplug_io_fn(struct backing_dev_info *unused_bdi, struct page *page)
{
swp_entry_t entry;
down_read(&swap_unplug_sem);
entry.val = page_private(page);
if (PageSwapCache(page)) {
struct block_device *bdev = swap_info[swp_type(entry)]->bdev;
struct backing_dev_info *bdi;
/*
* If the page is removed from swapcache from under us (with a
* racy try_to_unuse/swapoff) we need an additional reference
* count to avoid reading garbage from page_private(page) above.
* If the WARN_ON triggers during a swapoff it maybe the race
* condition and it's harmless. However if it triggers without
* swapoff it signals a problem.
*/
WARN_ON(page_count(page) <= 1);
bdi = bdev->bd_inode->i_mapping->backing_dev_info;
blk_run_backing_dev(bdi, page);
}
up_read(&swap_unplug_sem);
}
/*
* swapon tell device that all the old swap contents can be discarded,
* to allow the swap device to optimize its wear-levelling.
*/
static int discard_swap(struct swap_info_struct *si)
{
struct swap_extent *se;
sector_t start_block;
sector_t nr_blocks;
int err = 0;
/* Do not discard the swap header page! */
se = &si->first_swap_extent;
start_block = (se->start_block + 1) << (PAGE_SHIFT - 9);
nr_blocks = ((sector_t)se->nr_pages - 1) << (PAGE_SHIFT - 9);
if (nr_blocks) {
err = blkdev_issue_discard(si->bdev, start_block,
nr_blocks, GFP_KERNEL, 0);
if (err)
return err;
cond_resched();
}
list_for_each_entry(se, &si->first_swap_extent.list, list) {
start_block = se->start_block << (PAGE_SHIFT - 9);
nr_blocks = (sector_t)se->nr_pages << (PAGE_SHIFT - 9);
err = blkdev_issue_discard(si->bdev, start_block,
nr_blocks, GFP_KERNEL, 0);
if (err)
break;
cond_resched();
}
return err; /* That will often be -EOPNOTSUPP */
}
/*
* swap allocation tell device that a cluster of swap can now be discarded,
* to allow the swap device to optimize its wear-levelling.
*/
static void discard_swap_cluster(struct swap_info_struct *si,
pgoff_t start_page, pgoff_t nr_pages)
{
struct swap_extent *se = si->curr_swap_extent;
int found_extent = 0;
while (nr_pages) {
struct list_head *lh;
if (se->start_page <= start_page &&
start_page < se->start_page + se->nr_pages) {
pgoff_t offset = start_page - se->start_page;
sector_t start_block = se->start_block + offset;
sector_t nr_blocks = se->nr_pages - offset;
if (nr_blocks > nr_pages)
nr_blocks = nr_pages;
start_page += nr_blocks;
nr_pages -= nr_blocks;
if (!found_extent++)
si->curr_swap_extent = se;
start_block <<= PAGE_SHIFT - 9;
nr_blocks <<= PAGE_SHIFT - 9;
if (blkdev_issue_discard(si->bdev, start_block,
nr_blocks, GFP_NOIO, 0))
break;
}
lh = se->list.next;
se = list_entry(lh, struct swap_extent, list);
}
}
static int wait_for_discard(void *word)
{
schedule();
return 0;
}
#define SWAPFILE_CLUSTER 256
#define LATENCY_LIMIT 256
static inline unsigned long scan_swap_map(struct swap_info_struct *si,
unsigned char usage)
{
unsigned long offset;
unsigned long scan_base;
unsigned long last_in_cluster = 0;
int latency_ration = LATENCY_LIMIT;
int found_free_cluster = 0;
/*
* We try to cluster swap pages by allocating them sequentially
* in swap. Once we've allocated SWAPFILE_CLUSTER pages this
* way, however, we resort to first-free allocation, starting
* a new cluster. This prevents us from scattering swap pages
* all over the entire swap partition, so that we reduce
* overall disk seek times between swap pages. -- sct
* But we do now try to find an empty cluster. -Andrea
* And we let swap pages go all over an SSD partition. Hugh
*/
si->flags += SWP_SCANNING;
scan_base = offset = si->cluster_next;
if (unlikely(!si->cluster_nr--)) {
if (si->pages - si->inuse_pages < SWAPFILE_CLUSTER) {
si->cluster_nr = SWAPFILE_CLUSTER - 1;
goto checks;
}
if (si->flags & SWP_DISCARDABLE) {
/*
* Start range check on racing allocations, in case
* they overlap the cluster we eventually decide on
* (we scan without swap_lock to allow preemption).
* It's hardly conceivable that cluster_nr could be
* wrapped during our scan, but don't depend on it.
*/
if (si->lowest_alloc)
goto checks;
si->lowest_alloc = si->max;
si->highest_alloc = 0;
}
spin_unlock(&swap_lock);
/*
* If seek is expensive, start searching for new cluster from
* start of partition, to minimize the span of allocated swap.
* But if seek is cheap, search from our current position, so
* that swap is allocated from all over the partition: if the
* Flash Translation Layer only remaps within limited zones,
* we don't want to wear out the first zone too quickly.
*/
if (!(si->flags & SWP_SOLIDSTATE))
scan_base = offset = si->lowest_bit;
last_in_cluster = offset + SWAPFILE_CLUSTER - 1;
/* Locate the first empty (unaligned) cluster */
for (; last_in_cluster <= si->highest_bit; offset++) {
if (si->swap_map[offset])
last_in_cluster = offset + SWAPFILE_CLUSTER;
else if (offset == last_in_cluster) {
spin_lock(&swap_lock);
offset -= SWAPFILE_CLUSTER - 1;
si->cluster_next = offset;
si->cluster_nr = SWAPFILE_CLUSTER - 1;
found_free_cluster = 1;
goto checks;
}
if (unlikely(--latency_ration < 0)) {
cond_resched();
latency_ration = LATENCY_LIMIT;
}
}
offset = si->lowest_bit;
last_in_cluster = offset + SWAPFILE_CLUSTER - 1;
/* Locate the first empty (unaligned) cluster */
for (; last_in_cluster < scan_base; offset++) {
if (si->swap_map[offset])
last_in_cluster = offset + SWAPFILE_CLUSTER;
else if (offset == last_in_cluster) {
spin_lock(&swap_lock);
offset -= SWAPFILE_CLUSTER - 1;
si->cluster_next = offset;
si->cluster_nr = SWAPFILE_CLUSTER - 1;
found_free_cluster = 1;
goto checks;
}
if (unlikely(--latency_ration < 0)) {
cond_resched();
latency_ration = LATENCY_LIMIT;
}
}
offset = scan_base;
spin_lock(&swap_lock);
si->cluster_nr = SWAPFILE_CLUSTER - 1;
si->lowest_alloc = 0;
}
checks:
if (!(si->flags & SWP_WRITEOK))
goto no_page;
if (!si->highest_bit)
goto no_page;
if (offset > si->highest_bit)
scan_base = offset = si->lowest_bit;
/* reuse swap entry of cache-only swap if not busy. */
if (vm_swap_full() && si->swap_map[offset] == SWAP_HAS_CACHE) {
int swap_was_freed;
spin_unlock(&swap_lock);
swap_was_freed = __try_to_reclaim_swap(si, offset);
spin_lock(&swap_lock);
/* entry was freed successfully, try to use this again */
if (swap_was_freed)
goto checks;
goto scan; /* check next one */
}
if (si->swap_map[offset])
goto scan;
if (offset == si->lowest_bit)
si->lowest_bit++;
if (offset == si->highest_bit)
si->highest_bit--;
si->inuse_pages++;
if (si->inuse_pages == si->pages) {
si->lowest_bit = si->max;
si->highest_bit = 0;
}
si->swap_map[offset] = usage;
si->cluster_next = offset + 1;
si->flags -= SWP_SCANNING;
if (si->lowest_alloc) {
/*
* Only set when SWP_DISCARDABLE, and there's a scan
* for a free cluster in progress or just completed.
*/
if (found_free_cluster) {
/*
* To optimize wear-levelling, discard the
* old data of the cluster, taking care not to
* discard any of its pages that have already
* been allocated by racing tasks (offset has
* already stepped over any at the beginning).
*/
if (offset < si->highest_alloc &&
si->lowest_alloc <= last_in_cluster)
last_in_cluster = si->lowest_alloc - 1;
si->flags |= SWP_DISCARDING;
spin_unlock(&swap_lock);
if (offset < last_in_cluster)
discard_swap_cluster(si, offset,
last_in_cluster - offset + 1);
spin_lock(&swap_lock);
si->lowest_alloc = 0;
si->flags &= ~SWP_DISCARDING;
smp_mb(); /* wake_up_bit advises this */
wake_up_bit(&si->flags, ilog2(SWP_DISCARDING));
} else if (si->flags & SWP_DISCARDING) {
/*
* Delay using pages allocated by racing tasks
* until the whole discard has been issued. We
* could defer that delay until swap_writepage,
* but it's easier to keep this self-contained.
*/
spin_unlock(&swap_lock);
wait_on_bit(&si->flags, ilog2(SWP_DISCARDING),
wait_for_discard, TASK_UNINTERRUPTIBLE);
spin_lock(&swap_lock);
} else {
/*
* Note pages allocated by racing tasks while
* scan for a free cluster is in progress, so
* that its final discard can exclude them.
*/
if (offset < si->lowest_alloc)
si->lowest_alloc = offset;
if (offset > si->highest_alloc)
si->highest_alloc = offset;
}
}
return offset;
scan:
spin_unlock(&swap_lock);
while (++offset <= si->highest_bit) {
if (!si->swap_map[offset]) {
spin_lock(&swap_lock);
goto checks;
}
if (vm_swap_full() && si->swap_map[offset] == SWAP_HAS_CACHE) {
spin_lock(&swap_lock);
goto checks;
}
if (unlikely(--latency_ration < 0)) {
cond_resched();
latency_ration = LATENCY_LIMIT;
}
}
offset = si->lowest_bit;
while (++offset < scan_base) {
if (!si->swap_map[offset]) {
spin_lock(&swap_lock);
goto checks;
}
if (vm_swap_full() && si->swap_map[offset] == SWAP_HAS_CACHE) {
spin_lock(&swap_lock);
goto checks;
}
if (unlikely(--latency_ration < 0)) {
cond_resched();
latency_ration = LATENCY_LIMIT;
}
}
spin_lock(&swap_lock);
no_page:
si->flags -= SWP_SCANNING;
return 0;
}
swp_entry_t get_swap_page(void)
{
struct swap_info_struct *si;
pgoff_t offset;
int type, next;
int wrapped = 0;
spin_lock(&swap_lock);
if (nr_swap_pages <= 0)
goto noswap;
nr_swap_pages--;
for (type = swap_list.next; type >= 0 && wrapped < 2; type = next) {
si = swap_info[type];
next = si->next;
if (next < 0 ||
(!wrapped && si->prio != swap_info[next]->prio)) {
next = swap_list.head;
wrapped++;
}
if (!si->highest_bit)
continue;
if (!(si->flags & SWP_WRITEOK))
continue;
swap_list.next = next;
/* This is called for allocating swap entry for cache */
offset = scan_swap_map(si, SWAP_HAS_CACHE);
if (offset) {
spin_unlock(&swap_lock);
return swp_entry(type, offset);
}
next = swap_list.next;
}
nr_swap_pages++;
noswap:
spin_unlock(&swap_lock);
return (swp_entry_t) {0};
}
/* The only caller of this function is now susupend routine */
swp_entry_t get_swap_page_of_type(int type)
{
struct swap_info_struct *si;
pgoff_t offset;
spin_lock(&swap_lock);
si = swap_info[type];
if (si && (si->flags & SWP_WRITEOK)) {
nr_swap_pages--;
/* This is called for allocating swap entry, not cache */
offset = scan_swap_map(si, 1);
if (offset) {
spin_unlock(&swap_lock);
return swp_entry(type, offset);
}
nr_swap_pages++;
}
spin_unlock(&swap_lock);
return (swp_entry_t) {0};
}
static struct swap_info_struct *swap_info_get(swp_entry_t entry)
{
struct swap_info_struct *p;
unsigned long offset, type;
if (!entry.val)
goto out;
type = swp_type(entry);
if (type >= nr_swapfiles)
goto bad_nofile;
p = swap_info[type];
if (!(p->flags & SWP_USED))
goto bad_device;
offset = swp_offset(entry);
if (offset >= p->max)
goto bad_offset;
if (!p->swap_map[offset])
goto bad_free;
spin_lock(&swap_lock);
return p;
bad_free:
printk(KERN_ERR "swap_free: %s%08lx\n", Unused_offset, entry.val);
goto out;
bad_offset:
printk(KERN_ERR "swap_free: %s%08lx\n", Bad_offset, entry.val);
goto out;
bad_device:
printk(KERN_ERR "swap_free: %s%08lx\n", Unused_file, entry.val);
goto out;
bad_nofile:
printk(KERN_ERR "swap_free: %s%08lx\n", Bad_file, entry.val);
out:
return NULL;
}
static unsigned char swap_entry_free(struct swap_info_struct *p,
swp_entry_t entry, unsigned char usage)
{
unsigned long offset = swp_offset(entry);
unsigned char count;
unsigned char has_cache;
count = p->swap_map[offset];
has_cache = count & SWAP_HAS_CACHE;
count &= ~SWAP_HAS_CACHE;
if (usage == SWAP_HAS_CACHE) {
VM_BUG_ON(!has_cache);
has_cache = 0;
} else if (count == SWAP_MAP_SHMEM) {
/*
* Or we could insist on shmem.c using a special
* swap_shmem_free() and free_shmem_swap_and_cache()...
*/
count = 0;
} else if ((count & ~COUNT_CONTINUED) <= SWAP_MAP_MAX) {
if (count == COUNT_CONTINUED) {
if (swap_count_continued(p, offset, count))
count = SWAP_MAP_MAX | COUNT_CONTINUED;
else
count = SWAP_MAP_MAX;
} else
count--;
}
if (!count)
mem_cgroup_uncharge_swap(entry);
usage = count | has_cache;
p->swap_map[offset] = usage;
/* free if no reference */
if (!usage) {
struct gendisk *disk = p->bdev->bd_disk;
if (offset < p->lowest_bit)
p->lowest_bit = offset;
if (offset > p->highest_bit)
p->highest_bit = offset;
if (swap_list.next >= 0 &&
p->prio > swap_info[swap_list.next]->prio)
swap_list.next = p->type;
nr_swap_pages++;
p->inuse_pages--;
if ((p->flags & SWP_BLKDEV) &&
disk->fops->swap_slot_free_notify)
disk->fops->swap_slot_free_notify(p->bdev, offset);
}
return usage;
}
/*
* Caller has made sure that the swapdevice corresponding to entry
* is still around or has not been recycled.
*/
void swap_free(swp_entry_t entry)
{
struct swap_info_struct *p;
p = swap_info_get(entry);
if (p) {
swap_entry_free(p, entry, 1);
spin_unlock(&swap_lock);
}
}
/*
* Called after dropping swapcache to decrease refcnt to swap entries.
*/
void swapcache_free(swp_entry_t entry, struct page *page)
{
struct swap_info_struct *p;
unsigned char count;
p = swap_info_get(entry);
if (p) {
count = swap_entry_free(p, entry, SWAP_HAS_CACHE);
if (page)
mem_cgroup_uncharge_swapcache(page, entry, count != 0);
spin_unlock(&swap_lock);
}
}
/*
* How many references to page are currently swapped out?
* This does not give an exact answer when swap count is continued,
* but does include the high COUNT_CONTINUED flag to allow for that.
*/
static inline int page_swapcount(struct page *page)
{
int count = 0;
struct swap_info_struct *p;
swp_entry_t entry;
entry.val = page_private(page);
p = swap_info_get(entry);
if (p) {
count = swap_count(p->swap_map[swp_offset(entry)]);
spin_unlock(&swap_lock);
}
return count;
}
/*
* We can write to an anon page without COW if there are no other references
* to it. And as a side-effect, free up its swap: because the old content
* on disk will never be read, and seeking back there to write new content
* later would only waste time away from clustering.
*/
int reuse_swap_page(struct page *page)
{
int count;
VM_BUG_ON(!PageLocked(page));
if (unlikely(PageKsm(page)))
return 0;
count = page_mapcount(page);
if (count <= 1 && PageSwapCache(page)) {
count += page_swapcount(page);
if (count == 1 && !PageWriteback(page)) {
delete_from_swap_cache(page);
SetPageDirty(page);
}
}
return count <= 1;
}
/*
* If swap is getting full, or if there are no more mappings of this page,
* then try_to_free_swap is called to free its swap space.
*/
int try_to_free_swap(struct page *page)
{
VM_BUG_ON(!PageLocked(page));
if (!PageSwapCache(page))
return 0;
if (PageWriteback(page))
return 0;
if (page_swapcount(page))
return 0;
/*
* Once hibernation has begun to create its image of memory,
* there's a danger that one of the calls to try_to_free_swap()
* - most probably a call from __try_to_reclaim_swap() while
* hibernation is allocating its own swap pages for the image,
* but conceivably even a call from memory reclaim - will free
* the swap from a page which has already been recorded in the
* image as a clean swapcache page, and then reuse its swap for
* another page of the image. On waking from hibernation, the
* original page might be freed under memory pressure, then
* later read back in from swap, now with the wrong data.
*
* Hibernation clears bits from gfp_allowed_mask to prevent
* memory reclaim from writing to disk, so check that here.
*/
if (!(gfp_allowed_mask & __GFP_IO))
return 0;
delete_from_swap_cache(page);
SetPageDirty(page);
return 1;
}
/*
* Free the swap entry like above, but also try to
* free the page cache entry if it is the last user.
*/
int free_swap_and_cache(swp_entry_t entry)
{
struct swap_info_struct *p;
struct page *page = NULL;
if (non_swap_entry(entry))
return 1;
p = swap_info_get(entry);
if (p) {
if (swap_entry_free(p, entry, 1) == SWAP_HAS_CACHE) {
page = find_get_page(&swapper_space, entry.val);
if (page && !trylock_page(page)) {
page_cache_release(page);
page = NULL;
}
}
spin_unlock(&swap_lock);
}
if (page) {
/*
* Not mapped elsewhere, or swap space full? Free it!
* Also recheck PageSwapCache now page is locked (above).
*/
if (PageSwapCache(page) && !PageWriteback(page) &&
(!page_mapped(page) || vm_swap_full())) {
delete_from_swap_cache(page);
SetPageDirty(page);
}
unlock_page(page);
page_cache_release(page);
}
return p != NULL;
}
#ifdef CONFIG_CGROUP_MEM_RES_CTLR
/**
* mem_cgroup_count_swap_user - count the user of a swap entry
* @ent: the swap entry to be checked
* @pagep: the pointer for the swap cache page of the entry to be stored
*
* Returns the number of the user of the swap entry. The number is valid only
* for swaps of anonymous pages.
* If the entry is found on swap cache, the page is stored to pagep with
* refcount of it being incremented.
*/
int mem_cgroup_count_swap_user(swp_entry_t ent, struct page **pagep)
{
struct page *page;
struct swap_info_struct *p;
int count = 0;
page = find_get_page(&swapper_space, ent.val);
if (page)
count += page_mapcount(page);
p = swap_info_get(ent);
if (p) {
count += swap_count(p->swap_map[swp_offset(ent)]);
spin_unlock(&swap_lock);
}
*pagep = page;
return count;
}
#endif
#ifdef CONFIG_HIBERNATION
/*
* Find the swap type that corresponds to given device (if any).
*
* @offset - number of the PAGE_SIZE-sized block of the device, starting
* from 0, in which the swap header is expected to be located.
*
* This is needed for the suspend to disk (aka swsusp).
*/
int swap_type_of(dev_t device, sector_t offset, struct block_device **bdev_p)
{
struct block_device *bdev = NULL;
int type;
if (device)
bdev = bdget(device);
spin_lock(&swap_lock);
for (type = 0; type < nr_swapfiles; type++) {
struct swap_info_struct *sis = swap_info[type];
if (!(sis->flags & SWP_WRITEOK))
continue;
if (!bdev) {
if (bdev_p)
*bdev_p = bdgrab(sis->bdev);
spin_unlock(&swap_lock);
return type;
}
if (bdev == sis->bdev) {
struct swap_extent *se = &sis->first_swap_extent;
if (se->start_block == offset) {
if (bdev_p)
*bdev_p = bdgrab(sis->bdev);
spin_unlock(&swap_lock);
bdput(bdev);
return type;
}
}
}
spin_unlock(&swap_lock);
if (bdev)
bdput(bdev);
return -ENODEV;
}
/*
* Get the (PAGE_SIZE) block corresponding to given offset on the swapdev
* corresponding to given index in swap_info (swap type).
*/
sector_t swapdev_block(int type, pgoff_t offset)
{
struct block_device *bdev;
if ((unsigned int)type >= nr_swapfiles)
return 0;
if (!(swap_info[type]->flags & SWP_WRITEOK))
return 0;
return map_swap_entry(swp_entry(type, offset), &bdev);
}
/*
* Return either the total number of swap pages of given type, or the number
* of free pages of that type (depending on @free)
*
* This is needed for software suspend
*/
unsigned int count_swap_pages(int type, int free)
{
unsigned int n = 0;
spin_lock(&swap_lock);
if ((unsigned int)type < nr_swapfiles) {
struct swap_info_struct *sis = swap_info[type];
if (sis->flags & SWP_WRITEOK) {
n = sis->pages;
if (free)
n -= sis->inuse_pages;
}
}
spin_unlock(&swap_lock);
return n;
}
#endif /* CONFIG_HIBERNATION */
/*
* No need to decide whether this PTE shares the swap entry with others,
* just let do_wp_page work it out if a write is requested later - to
* force COW, vm_page_prot omits write permission from any private vma.
*/
static int unuse_pte(struct vm_area_struct *vma, pmd_t *pmd,
unsigned long addr, swp_entry_t entry, struct page *page)
{
struct mem_cgroup *ptr = NULL;
spinlock_t *ptl;
pte_t *pte;
int ret = 1;
if (mem_cgroup_try_charge_swapin(vma->vm_mm, page, GFP_KERNEL, &ptr)) {
ret = -ENOMEM;
goto out_nolock;
}
pte = pte_offset_map_lock(vma->vm_mm, pmd, addr, &ptl);
if (unlikely(!pte_same(*pte, swp_entry_to_pte(entry)))) {
if (ret > 0)
mem_cgroup_cancel_charge_swapin(ptr);
ret = 0;
goto out;
}
dec_mm_counter(vma->vm_mm, MM_SWAPENTS);
inc_mm_counter(vma->vm_mm, MM_ANONPAGES);
get_page(page);
set_pte_at(vma->vm_mm, addr, pte,
pte_mkold(mk_pte(page, vma->vm_page_prot)));
page_add_anon_rmap(page, vma, addr);
mem_cgroup_commit_charge_swapin(page, ptr);
swap_free(entry);
/*
* Move the page to the active list so it is not
* immediately swapped out again after swapon.
*/
activate_page(page);
out:
pte_unmap_unlock(pte, ptl);
out_nolock:
return ret;
}
static int unuse_pte_range(struct vm_area_struct *vma, pmd_t *pmd,
unsigned long addr, unsigned long end,
swp_entry_t entry, struct page *page)
{
pte_t swp_pte = swp_entry_to_pte(entry);
pte_t *pte;
int ret = 0;
/*
* We don't actually need pte lock while scanning for swp_pte: since
* we hold page lock and mmap_sem, swp_pte cannot be inserted into the
* page table while we're scanning; though it could get zapped, and on
* some architectures (e.g. x86_32 with PAE) we might catch a glimpse
* of unmatched parts which look like swp_pte, so unuse_pte must
* recheck under pte lock. Scanning without pte lock lets it be
* preemptible whenever CONFIG_PREEMPT but not CONFIG_HIGHPTE.
*/
pte = pte_offset_map(pmd, addr);
do {
/*
* swapoff spends a _lot_ of time in this loop!
* Test inline before going to call unuse_pte.
*/
if (unlikely(pte_same(*pte, swp_pte))) {
pte_unmap(pte);
ret = unuse_pte(vma, pmd, addr, entry, page);
if (ret)
goto out;
pte = pte_offset_map(pmd, addr);
}
} while (pte++, addr += PAGE_SIZE, addr != end);
pte_unmap(pte - 1);
out:
return ret;
}
static inline int unuse_pmd_range(struct vm_area_struct *vma, pud_t *pud,
unsigned long addr, unsigned long end,
swp_entry_t entry, struct page *page)
{
pmd_t *pmd;
unsigned long next;
int ret;
pmd = pmd_offset(pud, addr);
do {
next = pmd_addr_end(addr, end);
if (unlikely(pmd_trans_huge(*pmd)))
continue;
if (pmd_none_or_clear_bad(pmd))
continue;
ret = unuse_pte_range(vma, pmd, addr, next, entry, page);
if (ret)
return ret;
} while (pmd++, addr = next, addr != end);
return 0;
}
static inline int unuse_pud_range(struct vm_area_struct *vma, pgd_t *pgd,
unsigned long addr, unsigned long end,
swp_entry_t entry, struct page *page)
{
pud_t *pud;
unsigned long next;
int ret;
pud = pud_offset(pgd, addr);
do {
next = pud_addr_end(addr, end);
if (pud_none_or_clear_bad(pud))
continue;
ret = unuse_pmd_range(vma, pud, addr, next, entry, page);
if (ret)
return ret;
} while (pud++, addr = next, addr != end);
return 0;
}
static int unuse_vma(struct vm_area_struct *vma,
swp_entry_t entry, struct page *page)
{