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/*
* linux/mm/swap_state.c
*
* Copyright (C) 1991, 1992, 1993, 1994 Linus Torvalds
* Swap reorganised 29.12.95, Stephen Tweedie
*
* Rewritten to use page cache, (C) 1998 Stephen Tweedie
*/
#include <linux/mm.h>
#include <linux/kernel_stat.h>
#include <linux/swap.h>
#include <linux/swapctl.h>
#include <linux/init.h>
#include <linux/pagemap.h>
#include <linux/smp_lock.h>
#include <asm/pgtable.h>
/*
* We may have stale swap cache pages in memory: notice
* them here and get rid of the unnecessary final write.
*/
static int swap_writepage(struct page *page)
{
if (remove_exclusive_swap_page(page)) {
UnlockPage(page);
return 0;
}
rw_swap_page(WRITE, page);
return 0;
}
static struct address_space_operations swap_aops = {
writepage: swap_writepage,
sync_page: block_sync_page,
};
struct address_space swapper_space = {
LIST_HEAD_INIT(swapper_space.clean_pages),
LIST_HEAD_INIT(swapper_space.dirty_pages),
LIST_HEAD_INIT(swapper_space.locked_pages),
0, /* nrpages */
&swap_aops,
};
#ifdef SWAP_CACHE_INFO
#define INC_CACHE_INFO(x) (swap_cache_info.x++)
static struct {
unsigned long add_total;
unsigned long del_total;
unsigned long find_success;
unsigned long find_total;
unsigned long noent_race;
unsigned long exist_race;
} swap_cache_info;
void show_swap_cache_info(void)
{
printk("Swap cache: add %lu, delete %lu, find %lu/%lu, race %lu+%lu\n",
swap_cache_info.add_total, swap_cache_info.del_total,
swap_cache_info.find_success, swap_cache_info.find_total,
swap_cache_info.noent_race, swap_cache_info.exist_race);
}
#else
#define INC_CACHE_INFO(x) do { } while (0)
#endif
int add_to_swap_cache(struct page *page, swp_entry_t entry)
{
if (page->mapping)
BUG();
if (!swap_duplicate(entry)) {
INC_CACHE_INFO(noent_race);
return -ENOENT;
}
if (add_to_page_cache_unique(page, &swapper_space, entry.val,
page_hash(&swapper_space, entry.val)) != 0) {
swap_free(entry);
INC_CACHE_INFO(exist_race);
return -EEXIST;
}
if (!PageLocked(page))
BUG();
if (!PageSwapCache(page))
BUG();
INC_CACHE_INFO(add_total);
return 0;
}
/*
* This must be called only on pages that have
* been verified to be in the swap cache.
*/
void __delete_from_swap_cache(struct page *page)
{
if (!PageLocked(page))
BUG();
if (!PageSwapCache(page))
BUG();
ClearPageDirty(page);
__remove_inode_page(page);
INC_CACHE_INFO(del_total);
}
/*
* This must be called only on pages that have
* been verified to be in the swap cache and locked.
* It will never put the page into the free list,
* the caller has a reference on the page.
*/
void delete_from_swap_cache(struct page *page)
{
swp_entry_t entry;
if (!PageLocked(page))
BUG();
if (unlikely(!block_flushpage(page, 0)))
BUG(); /* an anonymous page cannot have page->buffers set */
entry.val = page->index;
spin_lock(&pagecache_lock);
__delete_from_swap_cache(page);
spin_unlock(&pagecache_lock);
swap_free(entry);
page_cache_release(page);
}
/*
* Perform a free_page(), also freeing any swap cache associated with
* this page if it is the last user of the page. Can not do a lock_page,
* as we are holding the page_table_lock spinlock.
*/
void free_page_and_swap_cache(struct page *page)
{
/*
* If we are the only user, then try to free up the swap cache.
*
* Its ok to check for PageSwapCache without the page lock
* here because we are going to recheck again inside
* exclusive_swap_page() _with_ the lock.
* - Marcelo
*/
if (PageSwapCache(page) && !TryLockPage(page)) {
remove_exclusive_swap_page(page);
UnlockPage(page);
}
page_cache_release(page);
}
/*
* Lookup a swap entry in the swap cache. A found page will be returned
* unlocked and with its refcount incremented - we rely on the kernel
* lock getting page table operations atomic even if we drop the page
* lock before returning.
*/
struct page * lookup_swap_cache(swp_entry_t entry)
{
struct page *found;
found = find_get_page(&swapper_space, entry.val);
/*
* Unsafe to assert PageSwapCache and mapping on page found:
* if SMP nothing prevents swapoff from deleting this page from
* the swap cache at this moment. find_lock_page would prevent
* that, but no need to change: we _have_ got the right page.
*/
INC_CACHE_INFO(find_total);
if (found)
INC_CACHE_INFO(find_success);
return found;
}
/*
* Locate a page of swap in physical memory, reserving swap cache space
* and reading the disk if it is not already cached.
* A failure return means that either the page allocation failed or that
* the swap entry is no longer in use.
*/
struct page * read_swap_cache_async(swp_entry_t entry)
{
struct page *found_page, *new_page = NULL;
int err;
do {
/*
* First check the swap cache. Since this is normally
* called after lookup_swap_cache() failed, re-calling
* that would confuse statistics: use find_get_page()
* directly.
*/
found_page = find_get_page(&swapper_space, entry.val);
if (found_page)
break;
/*
* Get a new page to read into from swap.
*/
if (!new_page) {
new_page = alloc_page(GFP_HIGHUSER);
if (!new_page)
break; /* Out of memory */
}
/*
* Associate the page with swap entry in the swap cache.
* May fail (-ENOENT) if swap entry has been freed since
* our caller observed it. May fail (-EEXIST) if there
* is already a page associated with this entry in the
* swap cache: added by a racing read_swap_cache_async,
* or by try_to_swap_out (or shmem_writepage) re-using
* the just freed swap entry for an existing page.
*/
err = add_to_swap_cache(new_page, entry);
if (!err) {
/*
* Initiate read into locked page and return.
*/
rw_swap_page(READ, new_page);
return new_page;
}
} while (err != -ENOENT);
if (new_page)
page_cache_release(new_page);
return found_page;
}
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