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authorFathi Boudra <fathi.boudra@linaro.org>2013-04-28 09:33:08 +0300
committerFathi Boudra <fathi.boudra@linaro.org>2013-04-28 09:33:08 +0300
commit3b4bd47f8f4ed3aaf7c81c9b5d2d37ad79fadf4a (patch)
treeb9996006addfd7ae70a39672b76843b49aebc189 /mm/swapfile.c
downloadlinux-linaro-highbank-3b4bd47f8f4ed3aaf7c81c9b5d2d37ad79fadf4a.tar.gz
Imported Upstream version 3.9.0HEADupstream/3.9.0upstreammaster
Diffstat (limited to 'mm/swapfile.c')
-rw-r--r--mm/swapfile.c2549
1 files changed, 2549 insertions, 0 deletions
diff --git a/mm/swapfile.c b/mm/swapfile.c
new file mode 100644
index 00000000..a1f7772a
--- /dev/null
+++ b/mm/swapfile.c
@@ -0,0 +1,2549 @@
+/*
+ * 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/shmem_fs.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/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 <linux/oom.h>
+#include <linux/frontswap.h>
+#include <linux/swapfile.h>
+#include <linux/export.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**);
+
+DEFINE_SPINLOCK(swap_lock);
+static unsigned int nr_swapfiles;
+atomic_long_t nr_swap_pages;
+/* protected with swap_lock. reading in vm_swap_full() doesn't need lock */
+long total_swap_pages;
+static int least_priority;
+static atomic_t highest_priority_index = ATOMIC_INIT(-1);
+
+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 ";
+
+struct swap_list_t swap_list = {-1, -1};
+
+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(swap_address_space(entry), 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;
+}
+
+/*
+ * 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 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(&si->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(&si->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(&si->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(&si->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(&si->lock);
+ swap_was_freed = __try_to_reclaim_swap(si, offset);
+ spin_lock(&si->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(&si->lock);
+
+ if (offset < last_in_cluster)
+ discard_swap_cluster(si, offset,
+ last_in_cluster - offset + 1);
+
+ spin_lock(&si->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(&si->lock);
+ wait_on_bit(&si->flags, ilog2(SWP_DISCARDING),
+ wait_for_discard, TASK_UNINTERRUPTIBLE);
+ spin_lock(&si->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(&si->lock);
+ while (++offset <= si->highest_bit) {
+ if (!si->swap_map[offset]) {
+ spin_lock(&si->lock);
+ goto checks;
+ }
+ if (vm_swap_full() && si->swap_map[offset] == SWAP_HAS_CACHE) {
+ spin_lock(&si->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(&si->lock);
+ goto checks;
+ }
+ if (vm_swap_full() && si->swap_map[offset] == SWAP_HAS_CACHE) {
+ spin_lock(&si->lock);
+ goto checks;
+ }
+ if (unlikely(--latency_ration < 0)) {
+ cond_resched();
+ latency_ration = LATENCY_LIMIT;
+ }
+ }
+ spin_lock(&si->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;
+ int hp_index;
+
+ spin_lock(&swap_lock);
+ if (atomic_long_read(&nr_swap_pages) <= 0)
+ goto noswap;
+ atomic_long_dec(&nr_swap_pages);
+
+ for (type = swap_list.next; type >= 0 && wrapped < 2; type = next) {
+ hp_index = atomic_xchg(&highest_priority_index, -1);
+ /*
+ * highest_priority_index records current highest priority swap
+ * type which just frees swap entries. If its priority is
+ * higher than that of swap_list.next swap type, we use it. It
+ * isn't protected by swap_lock, so it can be an invalid value
+ * if the corresponding swap type is swapoff. We double check
+ * the flags here. It's even possible the swap type is swapoff
+ * and swapon again and its priority is changed. In such rare
+ * case, low prority swap type might be used, but eventually
+ * high priority swap will be used after several rounds of
+ * swap.
+ */
+ if (hp_index != -1 && hp_index != type &&
+ swap_info[type]->prio < swap_info[hp_index]->prio &&
+ (swap_info[hp_index]->flags & SWP_WRITEOK)) {
+ type = hp_index;
+ swap_list.next = type;
+ }
+
+ si = swap_info[type];
+ next = si->next;
+ if (next < 0 ||
+ (!wrapped && si->prio != swap_info[next]->prio)) {
+ next = swap_list.head;
+ wrapped++;
+ }
+
+ spin_lock(&si->lock);
+ if (!si->highest_bit) {
+ spin_unlock(&si->lock);
+ continue;
+ }
+ if (!(si->flags & SWP_WRITEOK)) {
+ spin_unlock(&si->lock);
+ continue;
+ }
+
+ swap_list.next = next;
+
+ spin_unlock(&swap_lock);
+ /* This is called for allocating swap entry for cache */
+ offset = scan_swap_map(si, SWAP_HAS_CACHE);
+ spin_unlock(&si->lock);
+ if (offset)
+ return swp_entry(type, offset);
+ spin_lock(&swap_lock);
+ next = swap_list.next;
+ }
+
+ atomic_long_inc(&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;
+
+ si = swap_info[type];
+ spin_lock(&si->lock);
+ if (si && (si->flags & SWP_WRITEOK)) {
+ atomic_long_dec(&nr_swap_pages);
+ /* This is called for allocating swap entry, not cache */
+ offset = scan_swap_map(si, 1);
+ if (offset) {
+ spin_unlock(&si->lock);
+ return swp_entry(type, offset);
+ }
+ atomic_long_inc(&nr_swap_pages);
+ }
+ spin_unlock(&si->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(&p->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;
+}
+
+/*
+ * This swap type frees swap entry, check if it is the highest priority swap
+ * type which just frees swap entry. get_swap_page() uses
+ * highest_priority_index to search highest priority swap type. The
+ * swap_info_struct.lock can't protect us if there are multiple swap types
+ * active, so we use atomic_cmpxchg.
+ */
+static void set_highest_priority_index(int type)
+{
+ int old_hp_index, new_hp_index;
+
+ do {
+ old_hp_index = atomic_read(&highest_priority_index);
+ if (old_hp_index != -1 &&
+ swap_info[old_hp_index]->prio >= swap_info[type]->prio)
+ break;
+ new_hp_index = type;
+ } while (atomic_cmpxchg(&highest_priority_index,
+ old_hp_index, new_hp_index) != old_hp_index);
+}
+
+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) {
+ if (offset < p->lowest_bit)
+ p->lowest_bit = offset;
+ if (offset > p->highest_bit)
+ p->highest_bit = offset;
+ set_highest_priority_index(p->type);
+ atomic_long_inc(&nr_swap_pages);
+ p->inuse_pages--;
+ frontswap_invalidate_page(p->type, offset);
+ if (p->flags & SWP_BLKDEV) {
+ struct gendisk *disk = p->bdev->bd_disk;
+ if (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(&p->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(&p->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.
+ */
+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(&p->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.
+ *
+ * Hibration suspends storage while it is writing the image
+ * to disk so check that here.
+ */
+ if (pm_suspended_storage())
+ 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(swap_address_space(entry),
+ entry.val);
+ if (page && !trylock_page(page)) {
+ page_cache_release(page);
+ page = NULL;
+ }
+ }
+ spin_unlock(&p->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_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];
+
+ spin_lock(&sis->lock);
+ if (sis->flags & SWP_WRITEOK) {
+ n = sis->pages;
+ if (free)
+ n -= sis->inuse_pages;
+ }
+ spin_unlock(&sis->lock);
+ }
+ 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 page *swapcache;
+ struct mem_cgroup *memcg;
+ spinlock_t *ptl;
+ pte_t *pte;
+ int ret = 1;
+
+ swapcache = page;
+ page = ksm_might_need_to_copy(page, vma, addr);
+ if (unlikely(!page))
+ return -ENOMEM;
+
+ if (mem_cgroup_try_charge_swapin(vma->vm_mm, page,
+ GFP_KERNEL, &memcg)) {
+ 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)))) {
+ mem_cgroup_cancel_charge_swapin(memcg);
+ 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)));
+ if (page == swapcache)
+ page_add_anon_rmap(page, vma, addr);
+ else /* ksm created a completely new copy */
+ page_add_new_anon_rmap(page, vma, addr);
+ mem_cgroup_commit_charge_swapin(page, memcg);
+ 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:
+ if (page != swapcache) {
+ unlock_page(page);
+ put_page(page);
+ }
+ 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 (pmd_none_or_trans_huge_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)
+{
+ pgd_t *pgd;
+ unsigned long addr, end, next;
+ int ret;
+
+ if (page_anon_vma(page)) {
+ addr = page_address_in_vma(page, vma);
+ if (addr == -EFAULT)
+ return 0;
+ else
+ end = addr + PAGE_SIZE;
+ } else {
+ addr = vma->vm_start;
+ end = vma->vm_end;
+ }
+
+ pgd = pgd_offset(vma->vm_mm, addr);
+ do {
+ next = pgd_addr_end(addr, end);
+ if (pgd_none_or_clear_bad(pgd))
+ continue;
+ ret = unuse_pud_range(vma, pgd, addr, next, entry, page);
+ if (ret)
+ return ret;
+ } while (pgd++, addr = next, addr != end);
+ return 0;
+}
+
+static int unuse_mm(struct mm_struct *mm,
+ swp_entry_t entry, struct page *page)
+{
+ struct vm_area_struct *vma;
+ int ret = 0;
+
+ if (!down_read_trylock(&mm->mmap_sem)) {
+ /*
+ * Activate page so shrink_inactive_list is unlikely to unmap
+ * its ptes while lock is dropped, so swapoff can make progress.
+ */
+ activate_page(page);
+ unlock_page(page);
+ down_read(&mm->mmap_sem);
+ lock_page(page);
+ }
+ for (vma = mm->mmap; vma; vma = vma->vm_next) {
+ if (vma->anon_vma && (ret = unuse_vma(vma, entry, page)))
+ break;
+ }
+ up_read(&mm->mmap_sem);
+ return (ret < 0)? ret: 0;
+}
+
+/*
+ * Scan swap_map (or frontswap_map if frontswap parameter is true)
+ * from current position to next entry still in use.
+ * Recycle to start on reaching the end, returning 0 when empty.
+ */
+static unsigned int find_next_to_unuse(struct swap_info_struct *si,
+ unsigned int prev, bool frontswap)
+{
+ unsigned int max = si->max;
+ unsigned int i = prev;
+ unsigned char count;
+
+ /*
+ * No need for swap_lock here: we're just looking
+ * for whether an entry is in use, not modifying it; false
+ * hits are okay, and sys_swapoff() has already prevented new
+ * allocations from this area (while holding swap_lock).
+ */
+ for (;;) {
+ if (++i >= max) {
+ if (!prev) {
+ i = 0;
+ break;
+ }
+ /*
+ * No entries in use at top of swap_map,
+ * loop back to start and recheck there.
+ */
+ max = prev + 1;
+ prev = 0;
+ i = 1;
+ }
+ if (frontswap) {
+ if (frontswap_test(si, i))
+ break;
+ else
+ continue;
+ }
+ count = si->swap_map[i];
+ if (count && swap_count(count) != SWAP_MAP_BAD)
+ break;
+ }
+ return i;
+}
+
+/*
+ * We completely avoid races by reading each swap page in advance,
+ * and then search for the process using it. All the necessary
+ * page table adjustments can then be made atomically.
+ *
+ * if the boolean frontswap is true, only unuse pages_to_unuse pages;
+ * pages_to_unuse==0 means all pages; ignored if frontswap is false
+ */
+int try_to_unuse(unsigned int type, bool frontswap,
+ unsigned long pages_to_unuse)
+{
+ struct swap_info_struct *si = swap_info[type];
+ struct mm_struct *start_mm;
+ unsigned char *swap_map;
+ unsigned char swcount;
+ struct page *page;
+ swp_entry_t entry;
+ unsigned int i = 0;
+ int retval = 0;
+
+ /*
+ * When searching mms for an entry, a good strategy is to
+ * start at the first mm we freed the previous entry from
+ * (though actually we don't notice whether we or coincidence
+ * freed the entry). Initialize this start_mm with a hold.
+ *
+ * A simpler strategy would be to start at the last mm we
+ * freed the previous entry from; but that would take less
+ * advantage of mmlist ordering, which clusters forked mms
+ * together, child after parent. If we race with dup_mmap(), we
+ * prefer to resolve parent before child, lest we miss entries
+ * duplicated after we scanned child: using last mm would invert
+ * that.
+ */
+ start_mm = &init_mm;
+ atomic_inc(&init_mm.mm_users);
+
+ /*
+ * Keep on scanning until all entries have gone. Usually,
+ * one pass through swap_map is enough, but not necessarily:
+ * there are races when an instance of an entry might be missed.
+ */
+ while ((i = find_next_to_unuse(si, i, frontswap)) != 0) {
+ if (signal_pending(current)) {
+ retval = -EINTR;
+ break;
+ }
+
+ /*
+ * Get a page for the entry, using the existing swap
+ * cache page if there is one. Otherwise, get a clean
+ * page and read the swap into it.
+ */
+ swap_map = &si->swap_map[i];
+ entry = swp_entry(type, i);
+ page = read_swap_cache_async(entry,
+ GFP_HIGHUSER_MOVABLE, NULL, 0);
+ if (!page) {
+ /*
+ * Either swap_duplicate() failed because entry
+ * has been freed independently, and will not be
+ * reused since sys_swapoff() already disabled
+ * allocation from here, or alloc_page() failed.
+ */
+ if (!*swap_map)
+ continue;
+ retval = -ENOMEM;
+ break;
+ }
+
+ /*
+ * Don't hold on to start_mm if it looks like exiting.
+ */
+ if (atomic_read(&start_mm->mm_users) == 1) {
+ mmput(start_mm);
+ start_mm = &init_mm;
+ atomic_inc(&init_mm.mm_users);
+ }
+
+ /*
+ * Wait for and lock page. When do_swap_page races with
+ * try_to_unuse, do_swap_page can handle the fault much
+ * faster than try_to_unuse can locate the entry. This
+ * apparently redundant "wait_on_page_locked" lets try_to_unuse
+ * defer to do_swap_page in such a case - in some tests,
+ * do_swap_page and try_to_unuse repeatedly compete.
+ */
+ wait_on_page_locked(page);
+ wait_on_page_writeback(page);
+ lock_page(page);
+ wait_on_page_writeback(page);
+
+ /*
+ * Remove all references to entry.
+ */
+ swcount = *swap_map;
+ if (swap_count(swcount) == SWAP_MAP_SHMEM) {
+ retval = shmem_unuse(entry, page);
+ /* page has already been unlocked and released */
+ if (retval < 0)
+ break;
+ continue;
+ }
+ if (swap_count(swcount) && start_mm != &init_mm)
+ retval = unuse_mm(start_mm, entry, page);
+
+ if (swap_count(*swap_map)) {
+ int set_start_mm = (*swap_map >= swcount);
+ struct list_head *p = &start_mm->mmlist;
+ struct mm_struct *new_start_mm = start_mm;
+ struct mm_struct *prev_mm = start_mm;
+ struct mm_struct *mm;
+
+ atomic_inc(&new_start_mm->mm_users);
+ atomic_inc(&prev_mm->mm_users);
+ spin_lock(&mmlist_lock);
+ while (swap_count(*swap_map) && !retval &&
+ (p = p->next) != &start_mm->mmlist) {
+ mm = list_entry(p, struct mm_struct, mmlist);
+ if (!atomic_inc_not_zero(&mm->mm_users))
+ continue;
+ spin_unlock(&mmlist_lock);
+ mmput(prev_mm);
+ prev_mm = mm;
+
+ cond_resched();
+
+ swcount = *swap_map;
+ if (!swap_count(swcount)) /* any usage ? */
+ ;
+ else if (mm == &init_mm)
+ set_start_mm = 1;
+ else
+ retval = unuse_mm(mm, entry, page);
+
+ if (set_start_mm && *swap_map < swcount) {
+ mmput(new_start_mm);
+ atomic_inc(&mm->mm_users);
+ new_start_mm = mm;
+ set_start_mm = 0;
+ }
+ spin_lock(&mmlist_lock);
+ }
+ spin_unlock(&mmlist_lock);
+ mmput(prev_mm);
+ mmput(start_mm);
+ start_mm = new_start_mm;
+ }
+ if (retval) {
+ unlock_page(page);
+ page_cache_release(page);
+ break;
+ }
+
+ /*
+ * If a reference remains (rare), we would like to leave
+ * the page in the swap cache; but try_to_unmap could
+ * then re-duplicate the entry once we drop page lock,
+ * so we might loop indefinitely; also, that page could
+ * not be swapped out to other storage meanwhile. So:
+ * delete from cache even if there's another reference,
+ * after ensuring that the data has been saved to disk -
+ * since if the reference remains (rarer), it will be
+ * read from disk into another page. Splitting into two
+ * pages would be incorrect if swap supported "shared
+ * private" pages, but they are handled by tmpfs files.
+ *
+ * Given how unuse_vma() targets one particular offset
+ * in an anon_vma, once the anon_vma has been determined,
+ * this splitting happens to be just what is needed to
+ * handle where KSM pages have been swapped out: re-reading
+ * is unnecessarily slow, but we can fix that later on.
+ */
+ if (swap_count(*swap_map) &&
+ PageDirty(page) && PageSwapCache(page)) {
+ struct writeback_control wbc = {
+ .sync_mode = WB_SYNC_NONE,
+ };
+
+ swap_writepage(page, &wbc);
+ lock_page(page);
+ wait_on_page_writeback(page);
+ }
+
+ /*
+ * It is conceivable that a racing task removed this page from
+ * swap cache just before we acquired the page lock at the top,
+ * or while we dropped it in unuse_mm(). The page might even
+ * be back in swap cache on another swap area: that we must not
+ * delete, since it may not have been written out to swap yet.
+ */
+ if (PageSwapCache(page) &&
+ likely(page_private(page) == entry.val))
+ delete_from_swap_cache(page);
+
+ /*
+ * So we could skip searching mms once swap count went
+ * to 1, we did not mark any present ptes as dirty: must
+ * mark page dirty so shrink_page_list will preserve it.
+ */
+ SetPageDirty(page);
+ unlock_page(page);
+ page_cache_release(page);
+
+ /*
+ * Make sure that we aren't completely killing
+ * interactive performance.
+ */
+ cond_resched();
+ if (frontswap && pages_to_unuse > 0) {
+ if (!--pages_to_unuse)
+ break;
+ }
+ }
+
+ mmput(start_mm);
+ return retval;
+}
+
+/*
+ * After a successful try_to_unuse, if no swap is now in use, we know
+ * we can empty the mmlist. swap_lock must be held on entry and exit.
+ * Note that mmlist_lock nests inside swap_lock, and an mm must be
+ * added to the mmlist just after page_duplicate - before would be racy.
+ */
+static void drain_mmlist(void)
+{
+ struct list_head *p, *next;
+ unsigned int type;
+
+ for (type = 0; type < nr_swapfiles; type++)
+ if (swap_info[type]->inuse_pages)
+ return;
+ spin_lock(&mmlist_lock);
+ list_for_each_safe(p, next, &init_mm.mmlist)
+ list_del_init(p);
+ spin_unlock(&mmlist_lock);
+}
+
+/*
+ * Use this swapdev's extent info to locate the (PAGE_SIZE) block which
+ * corresponds to page offset for the specified swap entry.
+ * Note that the type of this function is sector_t, but it returns page offset
+ * into the bdev, not sector offset.
+ */
+static sector_t map_swap_entry(swp_entry_t entry, struct block_device **bdev)
+{
+ struct swap_info_struct *sis;
+ struct swap_extent *start_se;
+ struct swap_extent *se;
+ pgoff_t offset;
+
+ sis = swap_info[swp_type(entry)];
+ *bdev = sis->bdev;
+
+ offset = swp_offset(entry);
+ start_se = sis->curr_swap_extent;
+ se = start_se;
+
+ for ( ; ; ) {
+ struct list_head *lh;
+
+ if (se->start_page <= offset &&
+ offset < (se->start_page + se->nr_pages)) {
+ return se->start_block + (offset - se->start_page);
+ }
+ lh = se->list.next;
+ se = list_entry(lh, struct swap_extent, list);
+ sis->curr_swap_extent = se;
+ BUG_ON(se == start_se); /* It *must* be present */
+ }
+}
+
+/*
+ * Returns the page offset into bdev for the specified page's swap entry.
+ */
+sector_t map_swap_page(struct page *page, struct block_device **bdev)
+{
+ swp_entry_t entry;
+ entry.val = page_private(page);
+ return map_swap_entry(entry, bdev);
+}
+
+/*
+ * Free all of a swapdev's extent information
+ */
+static void destroy_swap_extents(struct swap_info_struct *sis)
+{
+ while (!list_empty(&sis->first_swap_extent.list)) {
+ struct swap_extent *se;
+
+ se = list_entry(sis->first_swap_extent.list.next,
+ struct swap_extent, list);
+ list_del(&se->list);
+ kfree(se);
+ }
+
+ if (sis->flags & SWP_FILE) {
+ struct file *swap_file = sis->swap_file;
+ struct address_space *mapping = swap_file->f_mapping;
+
+ sis->flags &= ~SWP_FILE;
+ mapping->a_ops->swap_deactivate(swap_file);
+ }
+}
+
+/*
+ * Add a block range (and the corresponding page range) into this swapdev's
+ * extent list. The extent list is kept sorted in page order.
+ *
+ * This function rather assumes that it is called in ascending page order.
+ */
+int
+add_swap_extent(struct swap_info_struct *sis, unsigned long start_page,
+ unsigned long nr_pages, sector_t start_block)
+{
+ struct swap_extent *se;
+ struct swap_extent *new_se;
+ struct list_head *lh;
+
+ if (start_page == 0) {
+ se = &sis->first_swap_extent;
+ sis->curr_swap_extent = se;
+ se->start_page = 0;
+ se->nr_pages = nr_pages;
+ se->start_block = start_block;
+ return 1;
+ } else {
+ lh = sis->first_swap_extent.list.prev; /* Highest extent */
+ se = list_entry(lh, struct swap_extent, list);
+ BUG_ON(se->start_page + se->nr_pages != start_page);
+ if (se->start_block + se->nr_pages == start_block) {
+ /* Merge it */
+ se->nr_pages += nr_pages;
+ return 0;
+ }
+ }
+
+ /*
+ * No merge. Insert a new extent, preserving ordering.
+ */
+ new_se = kmalloc(sizeof(*se), GFP_KERNEL);
+ if (new_se == NULL)
+ return -ENOMEM;
+ new_se->start_page = start_page;
+ new_se->nr_pages = nr_pages;
+ new_se->start_block = start_block;
+
+ list_add_tail(&new_se->list, &sis->first_swap_extent.list);
+ return 1;
+}
+
+/*
+ * A `swap extent' is a simple thing which maps a contiguous range of pages
+ * onto a contiguous range of disk blocks. An ordered list of swap extents
+ * is built at swapon time and is then used at swap_writepage/swap_readpage
+ * time for locating where on disk a page belongs.
+ *
+ * If the swapfile is an S_ISBLK block device, a single extent is installed.
+ * This is done so that the main operating code can treat S_ISBLK and S_ISREG
+ * swap files identically.
+ *
+ * Whether the swapdev is an S_ISREG file or an S_ISBLK blockdev, the swap
+ * extent list operates in PAGE_SIZE disk blocks. Both S_ISREG and S_ISBLK
+ * swapfiles are handled *identically* after swapon time.
+ *
+ * For S_ISREG swapfiles, setup_swap_extents() will walk all the file's blocks
+ * and will parse them into an ordered extent list, in PAGE_SIZE chunks. If
+ * some stray blocks are found which do not fall within the PAGE_SIZE alignment
+ * requirements, they are simply tossed out - we will never use those blocks
+ * for swapping.
+ *
+ * For S_ISREG swapfiles we set S_SWAPFILE across the life of the swapon. This
+ * prevents root from shooting her foot off by ftruncating an in-use swapfile,
+ * which will scribble on the fs.
+ *
+ * The amount of disk space which a single swap extent represents varies.
+ * Typically it is in the 1-4 megabyte range. So we can have hundreds of
+ * extents in the list. To avoid much list walking, we cache the previous
+ * search location in `curr_swap_extent', and start new searches from there.
+ * This is extremely effective. The average number of iterations in
+ * map_swap_page() has been measured at about 0.3 per page. - akpm.
+ */
+static int setup_swap_extents(struct swap_info_struct *sis, sector_t *span)
+{
+ struct file *swap_file = sis->swap_file;
+ struct address_space *mapping = swap_file->f_mapping;
+ struct inode *inode = mapping->host;
+ int ret;
+
+ if (S_ISBLK(inode->i_mode)) {
+ ret = add_swap_extent(sis, 0, sis->max, 0);
+ *span = sis->pages;
+ return ret;
+ }
+
+ if (mapping->a_ops->swap_activate) {
+ ret = mapping->a_ops->swap_activate(sis, swap_file, span);
+ if (!ret) {
+ sis->flags |= SWP_FILE;
+ ret = add_swap_extent(sis, 0, sis->max, 0);
+ *span = sis->pages;
+ }
+ return ret;
+ }
+
+ return generic_swapfile_activate(sis, swap_file, span);
+}
+
+static void _enable_swap_info(struct swap_info_struct *p, int prio,
+ unsigned char *swap_map,
+ unsigned long *frontswap_map)
+{
+ int i, prev;
+
+ if (prio >= 0)
+ p->prio = prio;
+ else
+ p->prio = --least_priority;
+ p->swap_map = swap_map;
+ frontswap_map_set(p, frontswap_map);
+ p->flags |= SWP_WRITEOK;
+ atomic_long_add(p->pages, &nr_swap_pages);
+ total_swap_pages += p->pages;
+
+ /* insert swap space into swap_list: */
+ prev = -1;
+ for (i = swap_list.head; i >= 0; i = swap_info[i]->next) {
+ if (p->prio >= swap_info[i]->prio)
+ break;
+ prev = i;
+ }
+ p->next = i;
+ if (prev < 0)
+ swap_list.head = swap_list.next = p->type;
+ else
+ swap_info[prev]->next = p->type;
+}
+
+static void enable_swap_info(struct swap_info_struct *p, int prio,
+ unsigned char *swap_map,
+ unsigned long *frontswap_map)
+{
+ spin_lock(&swap_lock);
+ spin_lock(&p->lock);
+ _enable_swap_info(p, prio, swap_map, frontswap_map);
+ frontswap_init(p->type);
+ spin_unlock(&p->lock);
+ spin_unlock(&swap_lock);
+}
+
+static void reinsert_swap_info(struct swap_info_struct *p)
+{
+ spin_lock(&swap_lock);
+ spin_lock(&p->lock);
+ _enable_swap_info(p, p->prio, p->swap_map, frontswap_map_get(p));
+ spin_unlock(&p->lock);
+ spin_unlock(&swap_lock);
+}
+
+SYSCALL_DEFINE1(swapoff, const char __user *, specialfile)
+{
+ struct swap_info_struct *p = NULL;
+ unsigned char *swap_map;
+ struct file *swap_file, *victim;
+ struct address_space *mapping;
+ struct inode *inode;
+ struct filename *pathname;
+ int i, type, prev;
+ int err;
+
+ if (!capable(CAP_SYS_ADMIN))
+ return -EPERM;
+
+ BUG_ON(!current->mm);
+
+ pathname = getname(specialfile);
+ if (IS_ERR(pathname))
+ return PTR_ERR(pathname);
+
+ victim = file_open_name(pathname, O_RDWR|O_LARGEFILE, 0);
+ err = PTR_ERR(victim);
+ if (IS_ERR(victim))
+ goto out;
+
+ mapping = victim->f_mapping;
+ prev = -1;
+ spin_lock(&swap_lock);
+ for (type = swap_list.head; type >= 0; type = swap_info[type]->next) {
+ p = swap_info[type];
+ if (p->flags & SWP_WRITEOK) {
+ if (p->swap_file->f_mapping == mapping)
+ break;
+ }
+ prev = type;
+ }
+ if (type < 0) {
+ err = -EINVAL;
+ spin_unlock(&swap_lock);
+ goto out_dput;
+ }
+ if (!security_vm_enough_memory_mm(current->mm, p->pages))
+ vm_unacct_memory(p->pages);
+ else {
+ err = -ENOMEM;
+ spin_unlock(&swap_lock);
+ goto out_dput;
+ }
+ if (prev < 0)
+ swap_list.head = p->next;
+ else
+ swap_info[prev]->next = p->next;
+ if (type == swap_list.next) {
+ /* just pick something that's safe... */
+ swap_list.next = swap_list.head;
+ }
+ spin_lock(&p->lock);
+ if (p->prio < 0) {
+ for (i = p->next; i >= 0; i = swap_info[i]->next)
+ swap_info[i]->prio = p->prio--;
+ least_priority++;
+ }
+ atomic_long_sub(p->pages, &nr_swap_pages);
+ total_swap_pages -= p->pages;
+ p->flags &= ~SWP_WRITEOK;
+ spin_unlock(&p->lock);
+ spin_unlock(&swap_lock);
+
+ set_current_oom_origin();
+ err = try_to_unuse(type, false, 0); /* force all pages to be unused */
+ clear_current_oom_origin();
+
+ if (err) {
+ /* re-insert swap space back into swap_list */
+ reinsert_swap_info(p);
+ goto out_dput;
+ }
+
+ destroy_swap_extents(p);
+ if (p->flags & SWP_CONTINUED)
+ free_swap_count_continuations(p);
+
+ mutex_lock(&swapon_mutex);
+ spin_lock(&swap_lock);
+ spin_lock(&p->lock);
+ drain_mmlist();
+
+ /* wait for anyone still in scan_swap_map */
+ p->highest_bit = 0; /* cuts scans short */
+ while (p->flags >= SWP_SCANNING) {
+ spin_unlock(&p->lock);
+ spin_unlock(&swap_lock);
+ schedule_timeout_uninterruptible(1);
+ spin_lock(&swap_lock);
+ spin_lock(&p->lock);
+ }
+
+ swap_file = p->swap_file;
+ p->swap_file = NULL;
+ p->max = 0;
+ swap_map = p->swap_map;
+ p->swap_map = NULL;
+ p->flags = 0;
+ frontswap_invalidate_area(type);
+ spin_unlock(&p->lock);
+ spin_unlock(&swap_lock);
+ mutex_unlock(&swapon_mutex);
+ vfree(swap_map);
+ vfree(frontswap_map_get(p));
+ /* Destroy swap account informatin */
+ swap_cgroup_swapoff(type);
+
+ inode = mapping->host;
+ if (S_ISBLK(inode->i_mode)) {
+ struct block_device *bdev = I_BDEV(inode);
+ set_blocksize(bdev, p->old_block_size);
+ blkdev_put(bdev, FMODE_READ | FMODE_WRITE | FMODE_EXCL);
+ } else {
+ mutex_lock(&inode->i_mutex);
+ inode->i_flags &= ~S_SWAPFILE;
+ mutex_unlock(&inode->i_mutex);
+ }
+ filp_close(swap_file, NULL);
+ err = 0;
+ atomic_inc(&proc_poll_event);
+ wake_up_interruptible(&proc_poll_wait);
+
+out_dput:
+ filp_close(victim, NULL);
+out:
+ putname(pathname);
+ return err;
+}
+
+#ifdef CONFIG_PROC_FS
+static unsigned swaps_poll(struct file *file, poll_table *wait)
+{
+ struct seq_file *seq = file->private_data;
+
+ poll_wait(file, &proc_poll_wait, wait);
+
+ if (seq->poll_event != atomic_read(&proc_poll_event)) {
+ seq->poll_event = atomic_read(&proc_poll_event);
+ return POLLIN | POLLRDNORM | POLLERR | POLLPRI;
+ }
+
+ return POLLIN | POLLRDNORM;
+}
+
+/* iterator */
+static void *swap_start(struct seq_file *swap, loff_t *pos)
+{
+ struct swap_info_struct *si;
+ int type;
+ loff_t l = *pos;
+
+ mutex_lock(&swapon_mutex);
+
+ if (!l)
+ return SEQ_START_TOKEN;
+
+ for (type = 0; type < nr_swapfiles; type++) {
+ smp_rmb(); /* read nr_swapfiles before swap_info[type] */
+ si = swap_info[type];
+ if (!(si->flags & SWP_USED) || !si->swap_map)
+ continue;
+ if (!--l)
+ return si;
+ }
+
+ return NULL;
+}
+
+static void *swap_next(struct seq_file *swap, void *v, loff_t *pos)
+{
+ struct swap_info_struct *si = v;
+ int type;
+
+ if (v == SEQ_START_TOKEN)
+ type = 0;
+ else
+ type = si->type + 1;
+
+ for (; type < nr_swapfiles; type++) {
+ smp_rmb(); /* read nr_swapfiles before swap_info[type] */
+ si = swap_info[type];
+ if (!(si->flags & SWP_USED) || !si->swap_map)
+ continue;
+ ++*pos;
+ return si;
+ }
+
+ return NULL;
+}
+
+static void swap_stop(struct seq_file *swap, void *v)
+{
+ mutex_unlock(&swapon_mutex);
+}
+
+static int swap_show(struct seq_file *swap, void *v)
+{
+ struct swap_info_struct *si = v;
+ struct file *file;
+ int len;
+
+ if (si == SEQ_START_TOKEN) {
+ seq_puts(swap,"Filename\t\t\t\tType\t\tSize\tUsed\tPriority\n");
+ return 0;
+ }
+
+ file = si->swap_file;
+ len = seq_path(swap, &file->f_path, " \t\n\\");
+ seq_printf(swap, "%*s%s\t%u\t%u\t%d\n",
+ len < 40 ? 40 - len : 1, " ",
+ S_ISBLK(file_inode(file)->i_mode) ?
+ "partition" : "file\t",
+ si->pages << (PAGE_SHIFT - 10),
+ si->inuse_pages << (PAGE_SHIFT - 10),
+ si->prio);
+ return 0;
+}
+
+static const struct seq_operations swaps_op = {
+ .start = swap_start,
+ .next = swap_next,
+ .stop = swap_stop,
+ .show = swap_show
+};
+
+static int swaps_open(struct inode *inode, struct file *file)
+{
+ struct seq_file *seq;
+ int ret;
+
+ ret = seq_open(file, &swaps_op);
+ if (ret)
+ return ret;
+
+ seq = file->private_data;
+ seq->poll_event = atomic_read(&proc_poll_event);
+ return 0;
+}
+
+static const struct file_operations proc_swaps_operations = {
+ .open = swaps_open,
+ .read = seq_read,
+ .llseek = seq_lseek,
+ .release = seq_release,
+ .poll = swaps_poll,
+};
+
+static int __init procswaps_init(void)
+{
+ proc_create("swaps", 0, NULL, &proc_swaps_operations);
+ return 0;
+}
+__initcall(procswaps_init);
+#endif /* CONFIG_PROC_FS */
+
+#ifdef MAX_SWAPFILES_CHECK
+static int __init max_swapfiles_check(void)
+{
+ MAX_SWAPFILES_CHECK();
+ return 0;
+}
+late_initcall(max_swapfiles_check);
+#endif
+
+static struct swap_info_struct *alloc_swap_info(void)
+{
+ struct swap_info_struct *p;
+ unsigned int type;
+
+ p = kzalloc(sizeof(*p), GFP_KERNEL);
+ if (!p)
+ return ERR_PTR(-ENOMEM);
+
+ spin_lock(&swap_lock);
+ for (type = 0; type < nr_swapfiles; type++) {
+ if (!(swap_info[type]->flags & SWP_USED))
+ break;
+ }
+ if (type >= MAX_SWAPFILES) {
+ spin_unlock(&swap_lock);
+ kfree(p);
+ return ERR_PTR(-EPERM);
+ }
+ if (type >= nr_swapfiles) {
+ p->type = type;
+ swap_info[type] = p;
+ /*
+ * Write swap_info[type] before nr_swapfiles, in case a
+ * racing procfs swap_start() or swap_next() is reading them.
+ * (We never shrink nr_swapfiles, we never free this entry.)
+ */
+ smp_wmb();
+ nr_swapfiles++;
+ } else {
+ kfree(p);
+ p = swap_info[type];
+ /*
+ * Do not memset this entry: a racing procfs swap_next()
+ * would be relying on p->type to remain valid.
+ */
+ }
+ INIT_LIST_HEAD(&p->first_swap_extent.list);
+ p->flags = SWP_USED;
+ p->next = -1;
+ spin_unlock(&swap_lock);
+ spin_lock_init(&p->lock);
+
+ return p;
+}
+
+static int claim_swapfile(struct swap_info_struct *p, struct inode *inode)
+{
+ int error;
+
+ if (S_ISBLK(inode->i_mode)) {
+ p->bdev = bdgrab(I_BDEV(inode));
+ error = blkdev_get(p->bdev,
+ FMODE_READ | FMODE_WRITE | FMODE_EXCL,
+ sys_swapon);
+ if (error < 0) {
+ p->bdev = NULL;
+ return -EINVAL;
+ }
+ p->old_block_size = block_size(p->bdev);
+ error = set_blocksize(p->bdev, PAGE_SIZE);
+ if (error < 0)
+ return error;
+ p->flags |= SWP_BLKDEV;
+ } else if (S_ISREG(inode->i_mode)) {
+ p->bdev = inode->i_sb->s_bdev;
+ mutex_lock(&inode->i_mutex);
+ if (IS_SWAPFILE(inode))
+ return -EBUSY;
+ } else
+ return -EINVAL;
+
+ return 0;
+}
+
+static unsigned long read_swap_header(struct swap_info_struct *p,
+ union swap_header *swap_header,
+ struct inode *inode)
+{
+ int i;
+ unsigned long maxpages;
+ unsigned long swapfilepages;
+
+ if (memcmp("SWAPSPACE2", swap_header->magic.magic, 10)) {
+ printk(KERN_ERR "Unable to find swap-space signature\n");
+ return 0;
+ }
+
+ /* swap partition endianess hack... */
+ if (swab32(swap_header->info.version) == 1) {
+ swab32s(&swap_header->info.version);
+ swab32s(&swap_header->info.last_page);
+ swab32s(&swap_header->info.nr_badpages);
+ for (i = 0; i < swap_header->info.nr_badpages; i++)
+ swab32s(&swap_header->info.badpages[i]);
+ }
+ /* Check the swap header's sub-version */
+ if (swap_header->info.version != 1) {
+ printk(KERN_WARNING
+ "Unable to handle swap header version %d\n",
+ swap_header->info.version);
+ return 0;
+ }
+
+ p->lowest_bit = 1;
+ p->cluster_next = 1;
+ p->cluster_nr = 0;
+
+ /*
+ * Find out how many pages are allowed for a single swap
+ * device. There are two limiting factors: 1) the number
+ * of bits for the swap offset in the swp_entry_t type, and
+ * 2) the number of bits in the swap pte as defined by the
+ * different architectures. In order to find the
+ * largest possible bit mask, a swap entry with swap type 0
+ * and swap offset ~0UL is created, encoded to a swap pte,
+ * decoded to a swp_entry_t again, and finally the swap
+ * offset is extracted. This will mask all the bits from
+ * the initial ~0UL mask that can't be encoded in either
+ * the swp_entry_t or the architecture definition of a
+ * swap pte.
+ */
+ maxpages = swp_offset(pte_to_swp_entry(
+ swp_entry_to_pte(swp_entry(0, ~0UL)))) + 1;
+ if (maxpages > swap_header->info.last_page) {
+ maxpages = swap_header->info.last_page + 1;
+ /* p->max is an unsigned int: don't overflow it */
+ if ((unsigned int)maxpages == 0)
+ maxpages = UINT_MAX;
+ }
+ p->highest_bit = maxpages - 1;
+
+ if (!maxpages)
+ return 0;
+ swapfilepages = i_size_read(inode) >> PAGE_SHIFT;
+ if (swapfilepages && maxpages > swapfilepages) {
+ printk(KERN_WARNING
+ "Swap area shorter than signature indicates\n");
+ return 0;
+ }
+ if (swap_header->info.nr_badpages && S_ISREG(inode->i_mode))
+ return 0;
+ if (swap_header->info.nr_badpages > MAX_SWAP_BADPAGES)
+ return 0;
+
+ return maxpages;
+}
+
+static int setup_swap_map_and_extents(struct swap_info_struct *p,
+ union swap_header *swap_header,
+ unsigned char *swap_map,
+ unsigned long maxpages,
+ sector_t *span)
+{
+ int i;
+ unsigned int nr_good_pages;
+ int nr_extents;
+
+ nr_good_pages = maxpages - 1; /* omit header page */
+
+ for (i = 0; i < swap_header->info.nr_badpages; i++) {
+ unsigned int page_nr = swap_header->info.badpages[i];
+ if (page_nr == 0 || page_nr > swap_header->info.last_page)
+ return -EINVAL;
+ if (page_nr < maxpages) {
+ swap_map[page_nr] = SWAP_MAP_BAD;
+ nr_good_pages--;
+ }
+ }
+
+ if (nr_good_pages) {
+ swap_map[0] = SWAP_MAP_BAD;
+ p->max = maxpages;
+ p->pages = nr_good_pages;
+ nr_extents = setup_swap_extents(p, span);
+ if (nr_extents < 0)
+ return nr_extents;
+ nr_good_pages = p->pages;
+ }
+ if (!nr_good_pages) {
+ printk(KERN_WARNING "Empty swap-file\n");
+ return -EINVAL;
+ }
+
+ return nr_extents;
+}
+
+SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags)
+{
+ struct swap_info_struct *p;
+ struct filename *name;
+ struct file *swap_file = NULL;
+ struct address_space *mapping;
+ int i;
+ int prio;
+ int error;
+ union swap_header *swap_header;
+ int nr_extents;
+ sector_t span;
+ unsigned long maxpages;
+ unsigned char *swap_map = NULL;
+ unsigned long *frontswap_map = NULL;
+ struct page *page = NULL;
+ struct inode *inode = NULL;
+
+ if (swap_flags & ~SWAP_FLAGS_VALID)
+ return -EINVAL;
+
+ if (!capable(CAP_SYS_ADMIN))
+ return -EPERM;
+
+ p = alloc_swap_info();
+ if (IS_ERR(p))
+ return PTR_ERR(p);
+
+ name = getname(specialfile);
+ if (IS_ERR(name)) {
+ error = PTR_ERR(name);
+ name = NULL;
+ goto bad_swap;
+ }
+ swap_file = file_open_name(name, O_RDWR|O_LARGEFILE, 0);
+ if (IS_ERR(swap_file)) {
+ error = PTR_ERR(swap_file);
+ swap_file = NULL;
+ goto bad_swap;
+ }
+
+ p->swap_file = swap_file;
+ mapping = swap_file->f_mapping;
+
+ for (i = 0; i < nr_swapfiles; i++) {
+ struct swap_info_struct *q = swap_info[i];
+
+ if (q == p || !q->swap_file)
+ continue;
+ if (mapping == q->swap_file->f_mapping) {
+ error = -EBUSY;
+ goto bad_swap;
+ }
+ }
+
+ inode = mapping->host;
+ /* If S_ISREG(inode->i_mode) will do mutex_lock(&inode->i_mutex); */
+ error = claim_swapfile(p, inode);
+ if (unlikely(error))
+ goto bad_swap;
+
+ /*
+ * Read the swap header.
+ */
+ if (!mapping->a_ops->readpage) {
+ error = -EINVAL;
+ goto bad_swap;
+ }
+ page = read_mapping_page(mapping, 0, swap_file);
+ if (IS_ERR(page)) {
+ error = PTR_ERR(page);
+ goto bad_swap;
+ }
+ swap_header = kmap(page);
+
+ maxpages = read_swap_header(p, swap_header, inode);
+ if (unlikely(!maxpages)) {
+ error = -EINVAL;
+ goto bad_swap;
+ }
+
+ /* OK, set up the swap map and apply the bad block list */
+ swap_map = vzalloc(maxpages);
+ if (!swap_map) {
+ error = -ENOMEM;
+ goto bad_swap;
+ }
+
+ error = swap_cgroup_swapon(p->type, maxpages);
+ if (error)
+ goto bad_swap;
+
+ nr_extents = setup_swap_map_and_extents(p, swap_header, swap_map,
+ maxpages, &span);
+ if (unlikely(nr_extents < 0)) {
+ error = nr_extents;
+ goto bad_swap;
+ }
+ /* frontswap enabled? set up bit-per-page map for frontswap */
+ if (frontswap_enabled)
+ frontswap_map = vzalloc(maxpages / sizeof(long));
+
+ if (p->bdev) {
+ if (blk_queue_nonrot(bdev_get_queue(p->bdev))) {
+ p->flags |= SWP_SOLIDSTATE;
+ p->cluster_next = 1 + (random32() % p->highest_bit);
+ }
+ if ((swap_flags & SWAP_FLAG_DISCARD) && discard_swap(p) == 0)
+ p->flags |= SWP_DISCARDABLE;
+ }
+
+ mutex_lock(&swapon_mutex);
+ prio = -1;
+ if (swap_flags & SWAP_FLAG_PREFER)
+ prio =
+ (swap_flags & SWAP_FLAG_PRIO_MASK) >> SWAP_FLAG_PRIO_SHIFT;
+ enable_swap_info(p, prio, swap_map, frontswap_map);
+
+ printk(KERN_INFO "Adding %uk swap on %s. "
+ "Priority:%d extents:%d across:%lluk %s%s%s\n",
+ p->pages<<(PAGE_SHIFT-10), name->name, p->prio,
+ nr_extents, (unsigned long long)span<<(PAGE_SHIFT-10),
+ (p->flags & SWP_SOLIDSTATE) ? "SS" : "",
+ (p->flags & SWP_DISCARDABLE) ? "D" : "",
+ (frontswap_map) ? "FS" : "");
+
+ mutex_unlock(&swapon_mutex);
+ atomic_inc(&proc_poll_event);
+ wake_up_interruptible(&proc_poll_wait);
+
+ if (S_ISREG(inode->i_mode))
+ inode->i_flags |= S_SWAPFILE;
+ error = 0;
+ goto out;
+bad_swap:
+ if (inode && S_ISBLK(inode->i_mode) && p->bdev) {
+ set_blocksize(p->bdev, p->old_block_size);
+ blkdev_put(p->bdev, FMODE_READ | FMODE_WRITE | FMODE_EXCL);
+ }
+ destroy_swap_extents(p);
+ swap_cgroup_swapoff(p->type);
+ spin_lock(&swap_lock);
+ p->swap_file = NULL;
+ p->flags = 0;
+ spin_unlock(&swap_lock);
+ vfree(swap_map);
+ if (swap_file) {
+ if (inode && S_ISREG(inode->i_mode)) {
+ mutex_unlock(&inode->i_mutex);
+ inode = NULL;
+ }
+ filp_close(swap_file, NULL);
+ }
+out:
+ if (page && !IS_ERR(page)) {
+ kunmap(page);
+ page_cache_release(page);
+ }
+ if (name)
+ putname(name);
+ if (inode && S_ISREG(inode->i_mode))
+ mutex_unlock(&inode->i_mutex);
+ return error;
+}
+
+void si_swapinfo(struct sysinfo *val)
+{
+ unsigned int type;
+ unsigned long nr_to_be_unused = 0;
+
+ spin_lock(&swap_lock);
+ for (type = 0; type < nr_swapfiles; type++) {
+ struct swap_info_struct *si = swap_info[type];
+
+ if ((si->flags & SWP_USED) && !(si->flags & SWP_WRITEOK))
+ nr_to_be_unused += si->inuse_pages;
+ }
+ val->freeswap = atomic_long_read(&nr_swap_pages) + nr_to_be_unused;
+ val->totalswap = total_swap_pages + nr_to_be_unused;
+ spin_unlock(&swap_lock);
+}
+
+/*
+ * Verify that a swap entry is valid and increment its swap map count.
+ *
+ * Returns error code in following case.
+ * - success -> 0
+ * - swp_entry is invalid -> EINVAL
+ * - swp_entry is migration entry -> EINVAL
+ * - swap-cache reference is requested but there is already one. -> EEXIST
+ * - swap-cache reference is requested but the entry is not used. -> ENOENT
+ * - swap-mapped reference requested but needs continued swap count. -> ENOMEM
+ */
+static int __swap_duplicate(swp_entry_t entry, unsigned char usage)
+{
+ struct swap_info_struct *p;
+ unsigned long offset, type;
+ unsigned char count;
+ unsigned char has_cache;
+ int err = -EINVAL;
+
+ if (non_swap_entry(entry))
+ goto out;
+
+ type = swp_type(entry);
+ if (type >= nr_swapfiles)
+ goto bad_file;
+ p = swap_info[type];
+ offset = swp_offset(entry);
+
+ spin_lock(&p->lock);
+ if (unlikely(offset >= p->max))
+ goto unlock_out;
+
+ count = p->swap_map[offset];
+ has_cache = count & SWAP_HAS_CACHE;
+ count &= ~SWAP_HAS_CACHE;
+ err = 0;
+
+ if (usage == SWAP_HAS_CACHE) {
+
+ /* set SWAP_HAS_CACHE if there is no cache and entry is used */
+ if (!has_cache && count)
+ has_cache = SWAP_HAS_CACHE;
+ else if (has_cache) /* someone else added cache */
+ err = -EEXIST;
+ else /* no users remaining */
+ err = -ENOENT;
+
+ } else if (count || has_cache) {
+
+ if ((count & ~COUNT_CONTINUED) < SWAP_MAP_MAX)
+ count += usage;
+ else if ((count & ~COUNT_CONTINUED) > SWAP_MAP_MAX)
+ err = -EINVAL;
+ else if (swap_count_continued(p, offset, count))
+ count = COUNT_CONTINUED;
+ else
+ err = -ENOMEM;
+ } else
+ err = -ENOENT; /* unused swap entry */
+
+ p->swap_map[offset] = count | has_cache;
+
+unlock_out:
+ spin_unlock(&p->lock);
+out:
+ return err;
+
+bad_file:
+ printk(KERN_ERR "swap_dup: %s%08lx\n", Bad_file, entry.val);
+ goto out;
+}
+
+/*
+ * Help swapoff by noting that swap entry belongs to shmem/tmpfs
+ * (in which case its reference count is never incremented).
+ */
+void swap_shmem_alloc(swp_entry_t entry)
+{
+ __swap_duplicate(entry, SWAP_MAP_SHMEM);
+}
+
+/*
+ * Increase reference count of swap entry by 1.
+ * Returns 0 for success, or -ENOMEM if a swap_count_continuation is required
+ * but could not be atomically allocated. Returns 0, just as if it succeeded,
+ * if __swap_duplicate() fails for another reason (-EINVAL or -ENOENT), which
+ * might occur if a page table entry has got corrupted.
+ */
+int swap_duplicate(swp_entry_t entry)
+{
+ int err = 0;
+
+ while (!err && __swap_duplicate(entry, 1) == -ENOMEM)
+ err = add_swap_count_continuation(entry, GFP_ATOMIC);
+ return err;
+}
+
+/*
+ * @entry: swap entry for which we allocate swap cache.
+ *
+ * Called when allocating swap cache for existing swap entry,
+ * This can return error codes. Returns 0 at success.
+ * -EBUSY means there is a swap cache.
+ * Note: return code is different from swap_duplicate().
+ */
+int swapcache_prepare(swp_entry_t entry)
+{
+ return __swap_duplicate(entry, SWAP_HAS_CACHE);
+}
+
+struct swap_info_struct *page_swap_info(struct page *page)
+{
+ swp_entry_t swap = { .val = page_private(page) };
+ BUG_ON(!PageSwapCache(page));
+ return swap_info[swp_type(swap)];
+}
+
+/*
+ * out-of-line __page_file_ methods to avoid include hell.
+ */
+struct address_space *__page_file_mapping(struct page *page)
+{
+ VM_BUG_ON(!PageSwapCache(page));
+ return page_swap_info(page)->swap_file->f_mapping;
+}
+EXPORT_SYMBOL_GPL(__page_file_mapping);
+
+pgoff_t __page_file_index(struct page *page)
+{
+ swp_entry_t swap = { .val = page_private(page) };
+ VM_BUG_ON(!PageSwapCache(page));
+ return swp_offset(swap);
+}
+EXPORT_SYMBOL_GPL(__page_file_index);
+
+/*
+ * add_swap_count_continuation - called when a swap count is duplicated
+ * beyond SWAP_MAP_MAX, it allocates a new page and links that to the entry's
+ * page of the original vmalloc'ed swap_map, to hold the continuation count
+ * (for that entry and for its neighbouring PAGE_SIZE swap entries). Called
+ * again when count is duplicated beyond SWAP_MAP_MAX * SWAP_CONT_MAX, etc.
+ *
+ * These continuation pages are seldom referenced: the common paths all work
+ * on the original swap_map, only referring to a continuation page when the
+ * low "digit" of a count is incremented or decremented through SWAP_MAP_MAX.
+ *
+ * add_swap_count_continuation(, GFP_ATOMIC) can be called while holding
+ * page table locks; if it fails, add_swap_count_continuation(, GFP_KERNEL)
+ * can be called after dropping locks.
+ */
+int add_swap_count_continuation(swp_entry_t entry, gfp_t gfp_mask)
+{
+ struct swap_info_struct *si;
+ struct page *head;
+ struct page *page;
+ struct page *list_page;
+ pgoff_t offset;
+ unsigned char count;
+
+ /*
+ * When debugging, it's easier to use __GFP_ZERO here; but it's better
+ * for latency not to zero a page while GFP_ATOMIC and holding locks.
+ */
+ page = alloc_page(gfp_mask | __GFP_HIGHMEM);
+
+ si = swap_info_get(entry);
+ if (!si) {
+ /*
+ * An acceptable race has occurred since the failing
+ * __swap_duplicate(): the swap entry has been freed,
+ * perhaps even the whole swap_map cleared for swapoff.
+ */
+ goto outer;
+ }
+
+ offset = swp_offset(entry);
+ count = si->swap_map[offset] & ~SWAP_HAS_CACHE;
+
+ if ((count & ~COUNT_CONTINUED) != SWAP_MAP_MAX) {
+ /*
+ * The higher the swap count, the more likely it is that tasks
+ * will race to add swap count continuation: we need to avoid
+ * over-provisioning.
+ */
+ goto out;
+ }
+
+ if (!page) {
+ spin_unlock(&si->lock);
+ return -ENOMEM;
+ }
+
+ /*
+ * We are fortunate that although vmalloc_to_page uses pte_offset_map,
+ * no architecture is using highmem pages for kernel pagetables: so it
+ * will not corrupt the GFP_ATOMIC caller's atomic pagetable kmaps.
+ */
+ head = vmalloc_to_page(si->swap_map + offset);
+ offset &= ~PAGE_MASK;
+
+ /*
+ * Page allocation does not initialize the page's lru field,
+ * but it does always reset its private field.
+ */
+ if (!page_private(head)) {
+ BUG_ON(count & COUNT_CONTINUED);
+ INIT_LIST_HEAD(&head->lru);
+ set_page_private(head, SWP_CONTINUED);
+ si->flags |= SWP_CONTINUED;
+ }
+
+ list_for_each_entry(list_page, &head->lru, lru) {
+ unsigned char *map;
+
+ /*
+ * If the previous map said no continuation, but we've found
+ * a continuation page, free our allocation and use this one.
+ */
+ if (!(count & COUNT_CONTINUED))
+ goto out;
+
+ map = kmap_atomic(list_page) + offset;
+ count = *map;
+ kunmap_atomic(map);
+
+ /*
+ * If this continuation count now has some space in it,
+ * free our allocation and use this one.
+ */
+ if ((count & ~COUNT_CONTINUED) != SWAP_CONT_MAX)
+ goto out;
+ }
+
+ list_add_tail(&page->lru, &head->lru);
+ page = NULL; /* now it's attached, don't free it */
+out:
+ spin_unlock(&si->lock);
+outer:
+ if (page)
+ __free_page(page);
+ return 0;
+}
+
+/*
+ * swap_count_continued - when the original swap_map count is incremented
+ * from SWAP_MAP_MAX, check if there is already a continuation page to carry
+ * into, carry if so, or else fail until a new continuation page is allocated;
+ * when the original swap_map count is decremented from 0 with continuation,
+ * borrow from the continuation and report whether it still holds more.
+ * Called while __swap_duplicate() or swap_entry_free() holds swap_lock.
+ */
+static bool swap_count_continued(struct swap_info_struct *si,
+ pgoff_t offset, unsigned char count)
+{
+ struct page *head;
+ struct page *page;
+ unsigned char *map;
+
+ head = vmalloc_to_page(si->swap_map + offset);
+ if (page_private(head) != SWP_CONTINUED) {
+ BUG_ON(count & COUNT_CONTINUED);
+ return false; /* need to add count continuation */
+ }
+
+ offset &= ~PAGE_MASK;
+ page = list_entry(head->lru.next, struct page, lru);
+ map = kmap_atomic(page) + offset;
+
+ if (count == SWAP_MAP_MAX) /* initial increment from swap_map */
+ goto init_map; /* jump over SWAP_CONT_MAX checks */
+
+ if (count == (SWAP_MAP_MAX | COUNT_CONTINUED)) { /* incrementing */
+ /*
+ * Think of how you add 1 to 999
+ */
+ while (*map == (SWAP_CONT_MAX | COUNT_CONTINUED)) {
+ kunmap_atomic(map);
+ page = list_entry(page->lru.next, struct page, lru);
+ BUG_ON(page == head);
+ map = kmap_atomic(page) + offset;
+ }
+ if (*map == SWAP_CONT_MAX) {
+ kunmap_atomic(map);
+ page = list_entry(page->lru.next, struct page, lru);
+ if (page == head)
+ return false; /* add count continuation */
+ map = kmap_atomic(page) + offset;
+init_map: *map = 0; /* we didn't zero the page */
+ }
+ *map += 1;
+ kunmap_atomic(map);
+ page = list_entry(page->lru.prev, struct page, lru);
+ while (page != head) {
+ map = kmap_atomic(page) + offset;
+ *map = COUNT_CONTINUED;
+ kunmap_atomic(map);
+ page = list_entry(page->lru.prev, struct page, lru);
+ }
+ return true; /* incremented */
+
+ } else { /* decrementing */
+ /*
+ * Think of how you subtract 1 from 1000
+ */
+ BUG_ON(count != COUNT_CONTINUED);
+ while (*map == COUNT_CONTINUED) {
+ kunmap_atomic(map);
+ page = list_entry(page->lru.next, struct page, lru);
+ BUG_ON(page == head);
+ map = kmap_atomic(page) + offset;
+ }
+ BUG_ON(*map == 0);
+ *map -= 1;
+ if (*map == 0)
+ count = 0;
+ kunmap_atomic(map);
+ page = list_entry(page->lru.prev, struct page, lru);
+ while (page != head) {
+ map = kmap_atomic(page) + offset;
+ *map = SWAP_CONT_MAX | count;
+ count = COUNT_CONTINUED;
+ kunmap_atomic(map);
+ page = list_entry(page->lru.prev, struct page, lru);
+ }
+ return count == COUNT_CONTINUED;
+ }
+}
+
+/*
+ * free_swap_count_continuations - swapoff free all the continuation pages
+ * appended to the swap_map, after swap_map is quiesced, before vfree'ing it.
+ */
+static void free_swap_count_continuations(struct swap_info_struct *si)
+{
+ pgoff_t offset;
+
+ for (offset = 0; offset < si->max; offset += PAGE_SIZE) {
+ struct page *head;
+ head = vmalloc_to_page(si->swap_map + offset);
+ if (page_private(head)) {
+ struct list_head *this, *next;
+ list_for_each_safe(this, next, &head->lru) {
+ struct page *page;
+ page = list_entry(this, struct page, lru);
+ list_del(this);
+ __free_page(page);
+ }
+ }
+ }
+}