1 files changed, 486 insertions, 0 deletions
diff --git a/mm/swap_state.c b/mm/swap_state.c
new file mode 100644
index 000000000..8bc8e6613
--- /dev/null
+++ b/mm/swap_state.c
@@ -0,0 +1,486 @@
+/*
+ *  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/gfp.h>
+#include <linux/kernel_stat.h>
+#include <linux/swap.h>
+#include <linux/swapops.h>
+#include <linux/init.h>
+#include <linux/pagemap.h>
+#include <linux/backing-dev.h>
+#include <linux/blkdev.h>
+#include <linux/pagevec.h>
+#include <linux/migrate.h>
+
+#include <asm/pgtable.h>
+
+/*
+ * swapper_space is a fiction, retained to simplify the path through
+ * vmscan's shrink_page_list.
+ */
+static const struct address_space_operations swap_aops = {
+	.writepage	= swap_writepage,
+	.set_page_dirty	= swap_set_page_dirty,
+#ifdef CONFIG_MIGRATION
+	.migratepage	= migrate_page,
+#endif
+};
+
+struct address_space swapper_spaces[MAX_SWAPFILES] = {
+	[0 ... MAX_SWAPFILES - 1] = {
+		.page_tree	= RADIX_TREE_INIT(GFP_ATOMIC|__GFP_NOWARN),
+		.i_mmap_writable = ATOMIC_INIT(0),
+		.a_ops		= &swap_aops,
+	}
+};
+
+#define INC_CACHE_INFO(x)	do { swap_cache_info.x++; } while (0)
+
+static struct {
+	unsigned long add_total;
+	unsigned long del_total;
+	unsigned long find_success;
+	unsigned long find_total;
+} swap_cache_info;
+
+unsigned long total_swapcache_pages(void)
+{
+	int i;
+	unsigned long ret = 0;
+
+	for (i = 0; i < MAX_SWAPFILES; i++)
+		ret += swapper_spaces[i].nrpages;
+	return ret;
+}
+
+static atomic_t swapin_readahead_hits = ATOMIC_INIT(4);
+
+void show_swap_cache_info(void)
+{
+	printk("%lu pages in swap cache\n", total_swapcache_pages());
+	printk("Swap cache stats: add %lu, delete %lu, find %lu/%lu\n",
+		swap_cache_info.add_total, swap_cache_info.del_total,
+		swap_cache_info.find_success, swap_cache_info.find_total);
+	printk("Free swap  = %ldkB\n",
+		get_nr_swap_pages() << (PAGE_SHIFT - 10));
+	printk("Total swap = %lukB\n", total_swap_pages << (PAGE_SHIFT - 10));
+}
+
+/*
+ * __add_to_swap_cache resembles add_to_page_cache_locked on swapper_space,
+ * but sets SwapCache flag and private instead of mapping and index.
+ */
+int __add_to_swap_cache(struct page *page, swp_entry_t entry)
+{
+	int error;
+	struct address_space *address_space;
+
+	VM_BUG_ON_PAGE(!PageLocked(page), page);
+	VM_BUG_ON_PAGE(PageSwapCache(page), page);
+	VM_BUG_ON_PAGE(!PageSwapBacked(page), page);
+
+	page_cache_get(page);
+	SetPageSwapCache(page);
+	set_page_private(page, entry.val);
+
+	address_space = swap_address_space(entry);
+	spin_lock_irq(&address_space->tree_lock);
+	error = radix_tree_insert(&address_space->page_tree,
+					entry.val, page);
+	if (likely(!error)) {
+		address_space->nrpages++;
+		__inc_zone_page_state(page, NR_FILE_PAGES);
+		INC_CACHE_INFO(add_total);
+	}
+	spin_unlock_irq(&address_space->tree_lock);
+
+	if (unlikely(error)) {
+		/*
+		 * Only the context which have set SWAP_HAS_CACHE flag
+		 * would call add_to_swap_cache().
+		 * So add_to_swap_cache() doesn't returns -EEXIST.
+		 */
+		VM_BUG_ON(error == -EEXIST);
+		set_page_private(page, 0UL);
+		ClearPageSwapCache(page);
+		page_cache_release(page);
+	}
+
+	return error;
+}
+
+
+int add_to_swap_cache(struct page *page, swp_entry_t entry, gfp_t gfp_mask)
+{
+	int error;
+
+	error = radix_tree_maybe_preload(gfp_mask);
+	if (!error) {
+		error = __add_to_swap_cache(page, entry);
+		radix_tree_preload_end();
+	}
+	return error;
+}
+
+/*
+ * 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)
+{
+	swp_entry_t entry;
+	struct address_space *address_space;
+
+	VM_BUG_ON_PAGE(!PageLocked(page), page);
+	VM_BUG_ON_PAGE(!PageSwapCache(page), page);
+	VM_BUG_ON_PAGE(PageWriteback(page), page);
+
+	entry.val = page_private(page);
+	address_space = swap_address_space(entry);
+	radix_tree_delete(&address_space->page_tree, page_private(page));
+	set_page_private(page, 0);
+	ClearPageSwapCache(page);
+	address_space->nrpages--;
+	__dec_zone_page_state(page, NR_FILE_PAGES);
+	INC_CACHE_INFO(del_total);
+}
+
+/**
+ * add_to_swap - allocate swap space for a page
+ * @page: page we want to move to swap
+ *
+ * Allocate swap space for the page and add the page to the
+ * swap cache.  Caller needs to hold the page lock. 
+ */
+int add_to_swap(struct page *page, struct list_head *list)
+{
+	swp_entry_t entry;
+	int err;
+
+	VM_BUG_ON_PAGE(!PageLocked(page), page);
+	VM_BUG_ON_PAGE(!PageUptodate(page), page);
+
+	entry = get_swap_page();
+	if (!entry.val)
+		return 0;
+
+	if (unlikely(PageTransHuge(page)))
+		if (unlikely(split_huge_page_to_list(page, list))) {
+			swapcache_free(entry);
+			return 0;
+		}
+
+	/*
+	 * Radix-tree node allocations from PF_MEMALLOC contexts could
+	 * completely exhaust the page allocator. __GFP_NOMEMALLOC
+	 * stops emergency reserves from being allocated.
+	 *
+	 * TODO: this could cause a theoretical memory reclaim
+	 * deadlock in the swap out path.
+	 */
+	/*
+	 * Add it to the swap cache and mark it dirty
+	 */
+	err = add_to_swap_cache(page, entry,
+			__GFP_HIGH|__GFP_NOMEMALLOC|__GFP_NOWARN);
+
+	if (!err) {	/* Success */
+		SetPageDirty(page);
+		return 1;
+	} else {	/* -ENOMEM radix-tree allocation failure */
+		/*
+		 * add_to_swap_cache() doesn't return -EEXIST, so we can safely
+		 * clear SWAP_HAS_CACHE flag.
+		 */
+		swapcache_free(entry);
+		return 0;
+	}
+}
+
+/*
+ * 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;
+	struct address_space *address_space;
+
+	entry.val = page_private(page);
+
+	address_space = swap_address_space(entry);
+	spin_lock_irq(&address_space->tree_lock);
+	__delete_from_swap_cache(page);
+	spin_unlock_irq(&address_space->tree_lock);
+
+	swapcache_free(entry);
+	page_cache_release(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
+ * try_to_free_swap() _with_ the lock.
+ * 					- Marcelo
+ */
+static inline void free_swap_cache(struct page *page)
+{
+	if (PageSwapCache(page) && !page_mapped(page) && trylock_page(page)) {
+		try_to_free_swap(page);
+		unlock_page(page);
+	}
+}
+
+/* 
+ * Perform a free_page(), also freeing any swap cache associated with
+ * this page if it is the last user of the page.
+ */
+void free_page_and_swap_cache(struct page *page)
+{
+	free_swap_cache(page);
+	page_cache_release(page);
+}
+
+/*
+ * Passed an array of pages, drop them all from swapcache and then release
+ * them.  They are removed from the LRU and freed if this is their last use.
+ */
+void free_pages_and_swap_cache(struct page **pages, int nr)
+{
+	struct page **pagep = pages;
+	int i;
+
+	lru_add_drain();
+	for (i = 0; i < nr; i++)
+		free_swap_cache(pagep[i]);
+	release_pages(pagep, nr, false);
+}
+
+/*
+ * 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 *page;
+
+	page = find_get_page(swap_address_space(entry), entry.val);
+
+	if (page) {
+		INC_CACHE_INFO(find_success);
+		if (TestClearPageReadahead(page))
+			atomic_inc(&swapin_readahead_hits);
+	}
+
+	INC_CACHE_INFO(find_total);
+	return page;
+}
+
+/* 
+ * 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, gfp_t gfp_mask,
+			struct vm_area_struct *vma, unsigned long addr)
+{
+	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.
+		 */
+		found_page = find_get_page(swap_address_space(entry),
+					entry.val);
+		if (found_page)
+			break;
+
+		/*
+		 * Get a new page to read into from swap.
+		 */
+		if (!new_page) {
+			new_page = alloc_page_vma(gfp_mask, vma, addr);
+			if (!new_page)
+				break;		/* Out of memory */
+		}
+
+		/*
+		 * call radix_tree_preload() while we can wait.
+		 */
+		err = radix_tree_maybe_preload(gfp_mask & GFP_KERNEL);
+		if (err)
+			break;
+
+		/*
+		 * Swap entry may have been freed since our caller observed it.
+		 */
+		err = swapcache_prepare(entry);
+		if (err == -EEXIST) {
+			radix_tree_preload_end();
+			/*
+			 * We might race against get_swap_page() and stumble
+			 * across a SWAP_HAS_CACHE swap_map entry whose page
+			 * has not been brought into the swapcache yet, while
+			 * the other end is scheduled away waiting on discard
+			 * I/O completion at scan_swap_map().
+			 *
+			 * In order to avoid turning this transitory state
+			 * into a permanent loop around this -EEXIST case
+			 * if !CONFIG_PREEMPT and the I/O completion happens
+			 * to be waiting on the CPU waitqueue where we are now
+			 * busy looping, we just conditionally invoke the
+			 * scheduler here, if there are some more important
+			 * tasks to run.
+			 */
+			cond_resched();
+			continue;
+		}
+		if (err) {		/* swp entry is obsolete ? */
+			radix_tree_preload_end();
+			break;
+		}
+
+		/* May fail (-ENOMEM) if radix-tree node allocation failed. */
+		__set_page_locked(new_page);
+		SetPageSwapBacked(new_page);
+		err = __add_to_swap_cache(new_page, entry);
+		if (likely(!err)) {
+			radix_tree_preload_end();
+			/*
+			 * Initiate read into locked page and return.
+			 */
+			lru_cache_add_anon(new_page);
+			swap_readpage(new_page);
+			return new_page;
+		}
+		radix_tree_preload_end();
+		ClearPageSwapBacked(new_page);
+		__clear_page_locked(new_page);
+		/*
+		 * add_to_swap_cache() doesn't return -EEXIST, so we can safely
+		 * clear SWAP_HAS_CACHE flag.
+		 */
+		swapcache_free(entry);
+	} while (err != -ENOMEM);
+
+	if (new_page)
+		page_cache_release(new_page);
+	return found_page;
+}
+
+static unsigned long swapin_nr_pages(unsigned long offset)
+{
+	static unsigned long prev_offset;
+	unsigned int pages, max_pages, last_ra;
+	static atomic_t last_readahead_pages;
+
+	max_pages = 1 << READ_ONCE(page_cluster);
+	if (max_pages <= 1)
+		return 1;
+
+	/*
+	 * This heuristic has been found to work well on both sequential and
+	 * random loads, swapping to hard disk or to SSD: please don't ask
+	 * what the "+ 2" means, it just happens to work well, that's all.
+	 */
+	pages = atomic_xchg(&swapin_readahead_hits, 0) + 2;
+	if (pages == 2) {
+		/*
+		 * We can have no readahead hits to judge by: but must not get
+		 * stuck here forever, so check for an adjacent offset instead
+		 * (and don't even bother to check whether swap type is same).
+		 */
+		if (offset != prev_offset + 1 && offset != prev_offset - 1)
+			pages = 1;
+		prev_offset = offset;
+	} else {
+		unsigned int roundup = 4;
+		while (roundup < pages)
+			roundup <<= 1;
+		pages = roundup;
+	}
+
+	if (pages > max_pages)
+		pages = max_pages;
+
+	/* Don't shrink readahead too fast */
+	last_ra = atomic_read(&last_readahead_pages) / 2;
+	if (pages < last_ra)
+		pages = last_ra;
+	atomic_set(&last_readahead_pages, pages);
+
+	return pages;
+}
+
+/**
+ * swapin_readahead - swap in pages in hope we need them soon
+ * @entry: swap entry of this memory
+ * @gfp_mask: memory allocation flags
+ * @vma: user vma this address belongs to
+ * @addr: target address for mempolicy
+ *
+ * Returns the struct page for entry and addr, after queueing swapin.
+ *
+ * Primitive swap readahead code. We simply read an aligned block of
+ * (1 << page_cluster) entries in the swap area. This method is chosen
+ * because it doesn't cost us any seek time.  We also make sure to queue
+ * the 'original' request together with the readahead ones...
+ *
+ * This has been extended to use the NUMA policies from the mm triggering
+ * the readahead.
+ *
+ * Caller must hold down_read on the vma->vm_mm if vma is not NULL.
+ */
+struct page *swapin_readahead(swp_entry_t entry, gfp_t gfp_mask,
+			struct vm_area_struct *vma, unsigned long addr)
+{
+	struct page *page;
+	unsigned long entry_offset = swp_offset(entry);
+	unsigned long offset = entry_offset;
+	unsigned long start_offset, end_offset;
+	unsigned long mask;
+	struct blk_plug plug;
+
+	mask = swapin_nr_pages(offset) - 1;
+	if (!mask)
+		goto skip;
+
+	/* Read a page_cluster sized and aligned cluster around offset. */
+	start_offset = offset & ~mask;
+	end_offset = offset | mask;
+	if (!start_offset)	/* First page is swap header. */
+		start_offset++;
+
+	blk_start_plug(&plug);
+	for (offset = start_offset; offset <= end_offset ; offset++) {
+		/* Ok, do the async read-ahead now */
+		page = read_swap_cache_async(swp_entry(swp_type(entry), offset),
+						gfp_mask, vma, addr);
+		if (!page)
+			continue;
+		if (offset != entry_offset)
+			SetPageReadahead(page);
+		page_cache_release(page);
+	}
+	blk_finish_plug(&plug);
+
+	lru_add_drain();	/* Push any new pages onto the LRU now */
+skip:
+	return read_swap_cache_async(entry, gfp_mask, vma, addr);
+}