| /* |
| * 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 <linux/delay.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, |
| /* swap cache doesn't use writeback related tags */ |
| .flags = 1 << AS_NO_WRITEBACK_TAGS, |
| } |
| }; |
| |
| #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); |
| |
| get_page(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, |
| swp_offset(entry), page); |
| if (likely(!error)) { |
| address_space->nrpages++; |
| __inc_node_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); |
| put_page(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, swp_offset(entry)); |
| set_page_private(page, 0); |
| ClearPageSwapCache(page); |
| address_space->nrpages--; |
| __dec_node_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 (mem_cgroup_try_charge_swap(page, entry)) { |
| swapcache_free(entry); |
| 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. |
| */ |
| err = add_to_swap_cache(page, entry, |
| __GFP_HIGH|__GFP_NOMEMALLOC|__GFP_NOWARN); |
| |
| if (!err) { |
| 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); |
| put_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 |
| * 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); |
| if (!is_huge_zero_page(page)) |
| put_page(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), swp_offset(entry)); |
| |
| if (page) { |
| INC_CACHE_INFO(find_success); |
| if (TestClearPageReadahead(page)) |
| atomic_inc(&swapin_readahead_hits); |
| } |
| |
| INC_CACHE_INFO(find_total); |
| return page; |
| } |
| |
| struct page *__read_swap_cache_async(swp_entry_t entry, gfp_t gfp_mask, |
| struct vm_area_struct *vma, unsigned long addr, |
| bool *new_page_allocated) |
| { |
| struct page *found_page, *new_page = NULL; |
| struct address_space *swapper_space = swap_address_space(entry); |
| int err; |
| *new_page_allocated = false; |
| |
| 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(swapper_space, swp_offset(entry)); |
| 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() may not work if the process is RT. |
| * We need a usleep_range() give up CPU to another task. |
| */ |
| usleep_range(500, 1000); |
| continue; |
| } |
| if (err) { /* swp entry is obsolete ? */ |
| radix_tree_preload_end(); |
| break; |
| } |
| |
| /* May fail (-ENOMEM) if radix-tree node allocation failed. */ |
| __SetPageLocked(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. |
| */ |
| SetPageWorkingset(new_page); |
| lru_cache_add_anon(new_page); |
| *new_page_allocated = true; |
| return new_page; |
| } |
| radix_tree_preload_end(); |
| __ClearPageLocked(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) |
| put_page(new_page); |
| return found_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) |
| { |
| bool page_was_allocated; |
| struct page *retpage = __read_swap_cache_async(entry, gfp_mask, |
| vma, addr, &page_was_allocated); |
| |
| if (page_was_allocated) |
| swap_readpage(retpage); |
| |
| return retpage; |
| } |
| |
| 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. |
| * This is needed to ensure the VMA will not be freed in our back. In the case |
| * of the speculative page fault handler, this cannot happen, even if we don't |
| * hold the mmap_sem. Callees are assumed to take care of reading VMA's fields |
| * using READ_ONCE() to read consistent values. |
| */ |
| 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 = is_swap_fast(entry) ? 0 : 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); |
| put_page(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); |
| } |