diff options
Diffstat (limited to 'mm/swap_state.c')
| -rw-r--r-- | mm/swap_state.c | 910 |
1 files changed, 910 insertions, 0 deletions
diff --git a/mm/swap_state.c b/mm/swap_state.c new file mode 100644 index 000000000..438d0676c --- /dev/null +++ b/mm/swap_state.c @@ -0,0 +1,910 @@ +// SPDX-License-Identifier: GPL-2.0 +/* + * 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/vmalloc.h> +#include <linux/swap_slots.h> +#include <linux/huge_mm.h> +#include <linux/shmem_fs.h> +#include "internal.h" +#include "swap.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, + .dirty_folio = noop_dirty_folio, +#ifdef CONFIG_MIGRATION + .migrate_folio = migrate_folio, +#endif +}; + +struct address_space *swapper_spaces[MAX_SWAPFILES] __read_mostly; +static unsigned int nr_swapper_spaces[MAX_SWAPFILES] __read_mostly; +static bool enable_vma_readahead __read_mostly = true; + +#define SWAP_RA_WIN_SHIFT (PAGE_SHIFT / 2) +#define SWAP_RA_HITS_MASK ((1UL << SWAP_RA_WIN_SHIFT) - 1) +#define SWAP_RA_HITS_MAX SWAP_RA_HITS_MASK +#define SWAP_RA_WIN_MASK (~PAGE_MASK & ~SWAP_RA_HITS_MASK) + +#define SWAP_RA_HITS(v) ((v) & SWAP_RA_HITS_MASK) +#define SWAP_RA_WIN(v) (((v) & SWAP_RA_WIN_MASK) >> SWAP_RA_WIN_SHIFT) +#define SWAP_RA_ADDR(v) ((v) & PAGE_MASK) + +#define SWAP_RA_VAL(addr, win, hits) \ + (((addr) & PAGE_MASK) | \ + (((win) << SWAP_RA_WIN_SHIFT) & SWAP_RA_WIN_MASK) | \ + ((hits) & SWAP_RA_HITS_MASK)) + +/* Initial readahead hits is 4 to start up with a small window */ +#define GET_SWAP_RA_VAL(vma) \ + (atomic_long_read(&(vma)->swap_readahead_info) ? : 4) + +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("Free swap = %ldkB\n", + get_nr_swap_pages() << (PAGE_SHIFT - 10)); + printk("Total swap = %lukB\n", total_swap_pages << (PAGE_SHIFT - 10)); +} + +void *get_shadow_from_swap_cache(swp_entry_t entry) +{ + struct address_space *address_space = swap_address_space(entry); + pgoff_t idx = swp_offset(entry); + struct page *page; + + page = xa_load(&address_space->i_pages, idx); + if (xa_is_value(page)) + return page; + return NULL; +} + +/* + * add_to_swap_cache resembles filemap_add_folio on swapper_space, + * but sets SwapCache flag and private instead of mapping and index. + */ +int add_to_swap_cache(struct folio *folio, swp_entry_t entry, + gfp_t gfp, void **shadowp) +{ + struct address_space *address_space = swap_address_space(entry); + pgoff_t idx = swp_offset(entry); + XA_STATE_ORDER(xas, &address_space->i_pages, idx, folio_order(folio)); + unsigned long i, nr = folio_nr_pages(folio); + void *old; + + VM_BUG_ON_FOLIO(!folio_test_locked(folio), folio); + VM_BUG_ON_FOLIO(folio_test_swapcache(folio), folio); + VM_BUG_ON_FOLIO(!folio_test_swapbacked(folio), folio); + + folio_ref_add(folio, nr); + folio_set_swapcache(folio); + + do { + xas_lock_irq(&xas); + xas_create_range(&xas); + if (xas_error(&xas)) + goto unlock; + for (i = 0; i < nr; i++) { + VM_BUG_ON_FOLIO(xas.xa_index != idx + i, folio); + old = xas_load(&xas); + if (xa_is_value(old)) { + if (shadowp) + *shadowp = old; + } + set_page_private(folio_page(folio, i), entry.val + i); + xas_store(&xas, folio); + xas_next(&xas); + } + address_space->nrpages += nr; + __node_stat_mod_folio(folio, NR_FILE_PAGES, nr); + __lruvec_stat_mod_folio(folio, NR_SWAPCACHE, nr); +unlock: + xas_unlock_irq(&xas); + } while (xas_nomem(&xas, gfp)); + + if (!xas_error(&xas)) + return 0; + + folio_clear_swapcache(folio); + folio_ref_sub(folio, nr); + return xas_error(&xas); +} + +/* + * This must be called only on folios that have + * been verified to be in the swap cache. + */ +void __delete_from_swap_cache(struct folio *folio, + swp_entry_t entry, void *shadow) +{ + struct address_space *address_space = swap_address_space(entry); + int i; + long nr = folio_nr_pages(folio); + pgoff_t idx = swp_offset(entry); + XA_STATE(xas, &address_space->i_pages, idx); + + VM_BUG_ON_FOLIO(!folio_test_locked(folio), folio); + VM_BUG_ON_FOLIO(!folio_test_swapcache(folio), folio); + VM_BUG_ON_FOLIO(folio_test_writeback(folio), folio); + + for (i = 0; i < nr; i++) { + void *entry = xas_store(&xas, shadow); + VM_BUG_ON_PAGE(entry != folio, entry); + set_page_private(folio_page(folio, i), 0); + xas_next(&xas); + } + folio_clear_swapcache(folio); + address_space->nrpages -= nr; + __node_stat_mod_folio(folio, NR_FILE_PAGES, -nr); + __lruvec_stat_mod_folio(folio, NR_SWAPCACHE, -nr); +} + +/** + * add_to_swap - allocate swap space for a folio + * @folio: folio we want to move to swap + * + * Allocate swap space for the folio and add the folio to the + * swap cache. + * + * Context: Caller needs to hold the folio lock. + * Return: Whether the folio was added to the swap cache. + */ +bool add_to_swap(struct folio *folio) +{ + swp_entry_t entry; + int err; + + VM_BUG_ON_FOLIO(!folio_test_locked(folio), folio); + VM_BUG_ON_FOLIO(!folio_test_uptodate(folio), folio); + + entry = folio_alloc_swap(folio); + if (!entry.val) + return false; + + /* + * XArray 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(folio, entry, + __GFP_HIGH|__GFP_NOMEMALLOC|__GFP_NOWARN, NULL); + if (err) + /* + * add_to_swap_cache() doesn't return -EEXIST, so we can safely + * clear SWAP_HAS_CACHE flag. + */ + goto fail; + /* + * Normally the folio will be dirtied in unmap because its + * pte should be dirty. A special case is MADV_FREE page. The + * page's pte could have dirty bit cleared but the folio's + * SwapBacked flag is still set because clearing the dirty bit + * and SwapBacked flag has no lock protected. For such folio, + * unmap will not set dirty bit for it, so folio reclaim will + * not write the folio out. This can cause data corruption when + * the folio is swapped in later. Always setting the dirty flag + * for the folio solves the problem. + */ + folio_mark_dirty(folio); + + return true; + +fail: + put_swap_folio(folio, entry); + return false; +} + +/* + * This must be called only on folios that have + * been verified to be in the swap cache and locked. + * It will never put the folio into the free list, + * the caller has a reference on the folio. + */ +void delete_from_swap_cache(struct folio *folio) +{ + swp_entry_t entry = folio_swap_entry(folio); + struct address_space *address_space = swap_address_space(entry); + + xa_lock_irq(&address_space->i_pages); + __delete_from_swap_cache(folio, entry, NULL); + xa_unlock_irq(&address_space->i_pages); + + put_swap_folio(folio, entry); + folio_ref_sub(folio, folio_nr_pages(folio)); +} + +void clear_shadow_from_swap_cache(int type, unsigned long begin, + unsigned long end) +{ + unsigned long curr = begin; + void *old; + + for (;;) { + swp_entry_t entry = swp_entry(type, curr); + struct address_space *address_space = swap_address_space(entry); + XA_STATE(xas, &address_space->i_pages, curr); + + xa_lock_irq(&address_space->i_pages); + xas_for_each(&xas, old, end) { + if (!xa_is_value(old)) + continue; + xas_store(&xas, NULL); + } + xa_unlock_irq(&address_space->i_pages); + + /* search the next swapcache until we meet end */ + curr >>= SWAP_ADDRESS_SPACE_SHIFT; + curr++; + curr <<= SWAP_ADDRESS_SPACE_SHIFT; + if (curr > end) + break; + } +} + +/* + * If we are the only user, then try to free up the swap cache. + * + * Its ok to check the swapcache flag without the folio lock + * here because we are going to recheck again inside + * folio_free_swap() _with_ the lock. + * - Marcelo + */ +void free_swap_cache(struct page *page) +{ + struct folio *folio = page_folio(page); + + if (folio_test_swapcache(folio) && !folio_mapped(folio) && + folio_trylock(folio)) { + folio_free_swap(folio); + folio_unlock(folio); + } +} + +/* + * 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); +} + +static inline bool swap_use_vma_readahead(void) +{ + return READ_ONCE(enable_vma_readahead) && !atomic_read(&nr_rotate_swap); +} + +/* + * Lookup a swap entry in the swap cache. A found folio 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 folio + * lock before returning. + */ +struct folio *swap_cache_get_folio(swp_entry_t entry, + struct vm_area_struct *vma, unsigned long addr) +{ + struct folio *folio; + struct swap_info_struct *si; + + si = get_swap_device(entry); + if (!si) + return NULL; + folio = filemap_get_folio(swap_address_space(entry), swp_offset(entry)); + put_swap_device(si); + + if (folio) { + bool vma_ra = swap_use_vma_readahead(); + bool readahead; + + /* + * At the moment, we don't support PG_readahead for anon THP + * so let's bail out rather than confusing the readahead stat. + */ + if (unlikely(folio_test_large(folio))) + return folio; + + readahead = folio_test_clear_readahead(folio); + if (vma && vma_ra) { + unsigned long ra_val; + int win, hits; + + ra_val = GET_SWAP_RA_VAL(vma); + win = SWAP_RA_WIN(ra_val); + hits = SWAP_RA_HITS(ra_val); + if (readahead) + hits = min_t(int, hits + 1, SWAP_RA_HITS_MAX); + atomic_long_set(&vma->swap_readahead_info, + SWAP_RA_VAL(addr, win, hits)); + } + + if (readahead) { + count_vm_event(SWAP_RA_HIT); + if (!vma || !vma_ra) + atomic_inc(&swapin_readahead_hits); + } + } + + return folio; +} + +/** + * find_get_incore_page - Find and get a page from the page or swap caches. + * @mapping: The address_space to search. + * @index: The page cache index. + * + * This differs from find_get_page() in that it will also look for the + * page in the swap cache. + * + * Return: The found page or %NULL. + */ +struct page *find_get_incore_page(struct address_space *mapping, pgoff_t index) +{ + swp_entry_t swp; + struct swap_info_struct *si; + struct page *page = pagecache_get_page(mapping, index, + FGP_ENTRY | FGP_HEAD, 0); + + if (!page) + return page; + if (!xa_is_value(page)) + return find_subpage(page, index); + if (!shmem_mapping(mapping)) + return NULL; + + swp = radix_to_swp_entry(page); + /* There might be swapin error entries in shmem mapping. */ + if (non_swap_entry(swp)) + return NULL; + /* Prevent swapoff from happening to us */ + si = get_swap_device(swp); + if (!si) + return NULL; + page = find_get_page(swap_address_space(swp), swp_offset(swp)); + put_swap_device(si); + 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 swap_info_struct *si; + struct folio *folio; + void *shadow = NULL; + + *new_page_allocated = false; + + for (;;) { + int err; + /* + * First check the swap cache. Since this is normally + * called after swap_cache_get_folio() failed, re-calling + * that would confuse statistics. + */ + si = get_swap_device(entry); + if (!si) + return NULL; + folio = filemap_get_folio(swap_address_space(entry), + swp_offset(entry)); + put_swap_device(si); + if (folio) + return folio_file_page(folio, swp_offset(entry)); + + /* + * Just skip read ahead for unused swap slot. + * During swap_off when swap_slot_cache is disabled, + * we have to handle the race between putting + * swap entry in swap cache and marking swap slot + * as SWAP_HAS_CACHE. That's done in later part of code or + * else swap_off will be aborted if we return NULL. + */ + if (!__swp_swapcount(entry) && swap_slot_cache_enabled) + return NULL; + + /* + * Get a new page to read into from swap. Allocate it now, + * before marking swap_map SWAP_HAS_CACHE, when -EEXIST will + * cause any racers to loop around until we add it to cache. + */ + folio = vma_alloc_folio(gfp_mask, 0, vma, addr, false); + if (!folio) + return NULL; + + /* + * Swap entry may have been freed since our caller observed it. + */ + err = swapcache_prepare(entry); + if (!err) + break; + + folio_put(folio); + if (err != -EEXIST) + return NULL; + + /* + * We might race against __delete_from_swap_cache(), and + * stumble across a swap_map entry whose SWAP_HAS_CACHE + * has not yet been cleared. Or race against another + * __read_swap_cache_async(), which has set SWAP_HAS_CACHE + * in swap_map, but not yet added its page to swap cache. + */ + schedule_timeout_uninterruptible(1); + } + + /* + * The swap entry is ours to swap in. Prepare the new page. + */ + + __folio_set_locked(folio); + __folio_set_swapbacked(folio); + + if (mem_cgroup_swapin_charge_folio(folio, NULL, gfp_mask, entry)) + goto fail_unlock; + + /* May fail (-ENOMEM) if XArray node allocation failed. */ + if (add_to_swap_cache(folio, entry, gfp_mask & GFP_RECLAIM_MASK, &shadow)) + goto fail_unlock; + + mem_cgroup_swapin_uncharge_swap(entry); + + if (shadow) + workingset_refault(folio, shadow); + + /* Caller will initiate read into locked folio */ + folio_add_lru(folio); + *new_page_allocated = true; + return &folio->page; + +fail_unlock: + put_swap_folio(folio, entry); + folio_unlock(folio); + folio_put(folio); + return NULL; +} + +/* + * 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 do_poll, + struct swap_iocb **plug) +{ + 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, do_poll, plug); + + return retpage; +} + +static unsigned int __swapin_nr_pages(unsigned long prev_offset, + unsigned long offset, + int hits, + int max_pages, + int prev_win) +{ + unsigned int pages, last_ra; + + /* + * 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 = hits + 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; + } 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 = prev_win / 2; + if (pages < last_ra) + pages = last_ra; + + return pages; +} + +static unsigned long swapin_nr_pages(unsigned long offset) +{ + static unsigned long prev_offset; + unsigned int hits, pages, max_pages; + static atomic_t last_readahead_pages; + + max_pages = 1 << READ_ONCE(page_cluster); + if (max_pages <= 1) + return 1; + + hits = atomic_xchg(&swapin_readahead_hits, 0); + pages = __swapin_nr_pages(READ_ONCE(prev_offset), offset, hits, + max_pages, + atomic_read(&last_readahead_pages)); + if (!hits) + WRITE_ONCE(prev_offset, offset); + atomic_set(&last_readahead_pages, pages); + + return pages; +} + +/** + * swap_cluster_readahead - swap in pages in hope we need them soon + * @entry: swap entry of this memory + * @gfp_mask: memory allocation flags + * @vmf: fault information + * + * 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 read mmap_lock if vmf->vma is not NULL. + */ +struct page *swap_cluster_readahead(swp_entry_t entry, gfp_t gfp_mask, + struct vm_fault *vmf) +{ + 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 swap_info_struct *si = swp_swap_info(entry); + struct blk_plug plug; + struct swap_iocb *splug = NULL; + bool do_poll = true, page_allocated; + struct vm_area_struct *vma = vmf->vma; + unsigned long addr = vmf->address; + + mask = swapin_nr_pages(offset) - 1; + if (!mask) + goto skip; + + do_poll = false; + /* 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++; + if (end_offset >= si->max) + end_offset = si->max - 1; + + 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, &page_allocated); + if (!page) + continue; + if (page_allocated) { + swap_readpage(page, false, &splug); + if (offset != entry_offset) { + SetPageReadahead(page); + count_vm_event(SWAP_RA); + } + } + put_page(page); + } + blk_finish_plug(&plug); + swap_read_unplug(splug); + + lru_add_drain(); /* Push any new pages onto the LRU now */ +skip: + /* The page was likely read above, so no need for plugging here */ + return read_swap_cache_async(entry, gfp_mask, vma, addr, do_poll, NULL); +} + +int init_swap_address_space(unsigned int type, unsigned long nr_pages) +{ + struct address_space *spaces, *space; + unsigned int i, nr; + + nr = DIV_ROUND_UP(nr_pages, SWAP_ADDRESS_SPACE_PAGES); + spaces = kvcalloc(nr, sizeof(struct address_space), GFP_KERNEL); + if (!spaces) + return -ENOMEM; + for (i = 0; i < nr; i++) { + space = spaces + i; + xa_init_flags(&space->i_pages, XA_FLAGS_LOCK_IRQ); + atomic_set(&space->i_mmap_writable, 0); + space->a_ops = &swap_aops; + /* swap cache doesn't use writeback related tags */ + mapping_set_no_writeback_tags(space); + } + nr_swapper_spaces[type] = nr; + swapper_spaces[type] = spaces; + + return 0; +} + +void exit_swap_address_space(unsigned int type) +{ + int i; + struct address_space *spaces = swapper_spaces[type]; + + for (i = 0; i < nr_swapper_spaces[type]; i++) + VM_WARN_ON_ONCE(!mapping_empty(&spaces[i])); + kvfree(spaces); + nr_swapper_spaces[type] = 0; + swapper_spaces[type] = NULL; +} + +static inline void swap_ra_clamp_pfn(struct vm_area_struct *vma, + unsigned long faddr, + unsigned long lpfn, + unsigned long rpfn, + unsigned long *start, + unsigned long *end) +{ + *start = max3(lpfn, PFN_DOWN(vma->vm_start), + PFN_DOWN(faddr & PMD_MASK)); + *end = min3(rpfn, PFN_DOWN(vma->vm_end), + PFN_DOWN((faddr & PMD_MASK) + PMD_SIZE)); +} + +static void swap_ra_info(struct vm_fault *vmf, + struct vma_swap_readahead *ra_info) +{ + struct vm_area_struct *vma = vmf->vma; + unsigned long ra_val; + unsigned long faddr, pfn, fpfn; + unsigned long start, end; + pte_t *pte, *orig_pte; + unsigned int max_win, hits, prev_win, win, left; +#ifndef CONFIG_64BIT + pte_t *tpte; +#endif + + max_win = 1 << min_t(unsigned int, READ_ONCE(page_cluster), + SWAP_RA_ORDER_CEILING); + if (max_win == 1) { + ra_info->win = 1; + return; + } + + faddr = vmf->address; + orig_pte = pte = pte_offset_map(vmf->pmd, faddr); + + fpfn = PFN_DOWN(faddr); + ra_val = GET_SWAP_RA_VAL(vma); + pfn = PFN_DOWN(SWAP_RA_ADDR(ra_val)); + prev_win = SWAP_RA_WIN(ra_val); + hits = SWAP_RA_HITS(ra_val); + ra_info->win = win = __swapin_nr_pages(pfn, fpfn, hits, + max_win, prev_win); + atomic_long_set(&vma->swap_readahead_info, + SWAP_RA_VAL(faddr, win, 0)); + + if (win == 1) { + pte_unmap(orig_pte); + return; + } + + /* Copy the PTEs because the page table may be unmapped */ + if (fpfn == pfn + 1) + swap_ra_clamp_pfn(vma, faddr, fpfn, fpfn + win, &start, &end); + else if (pfn == fpfn + 1) + swap_ra_clamp_pfn(vma, faddr, fpfn - win + 1, fpfn + 1, + &start, &end); + else { + left = (win - 1) / 2; + swap_ra_clamp_pfn(vma, faddr, fpfn - left, fpfn + win - left, + &start, &end); + } + ra_info->nr_pte = end - start; + ra_info->offset = fpfn - start; + pte -= ra_info->offset; +#ifdef CONFIG_64BIT + ra_info->ptes = pte; +#else + tpte = ra_info->ptes; + for (pfn = start; pfn != end; pfn++) + *tpte++ = *pte++; +#endif + pte_unmap(orig_pte); +} + +/** + * swap_vma_readahead - swap in pages in hope we need them soon + * @fentry: swap entry of this memory + * @gfp_mask: memory allocation flags + * @vmf: fault information + * + * Returns the struct page for entry and addr, after queueing swapin. + * + * Primitive swap readahead code. We simply read in a few pages whose + * virtual addresses are around the fault address in the same vma. + * + * Caller must hold read mmap_lock if vmf->vma is not NULL. + * + */ +static struct page *swap_vma_readahead(swp_entry_t fentry, gfp_t gfp_mask, + struct vm_fault *vmf) +{ + struct blk_plug plug; + struct swap_iocb *splug = NULL; + struct vm_area_struct *vma = vmf->vma; + struct page *page; + pte_t *pte, pentry; + swp_entry_t entry; + unsigned int i; + bool page_allocated; + struct vma_swap_readahead ra_info = { + .win = 1, + }; + + swap_ra_info(vmf, &ra_info); + if (ra_info.win == 1) + goto skip; + + blk_start_plug(&plug); + for (i = 0, pte = ra_info.ptes; i < ra_info.nr_pte; + i++, pte++) { + pentry = *pte; + if (!is_swap_pte(pentry)) + continue; + entry = pte_to_swp_entry(pentry); + if (unlikely(non_swap_entry(entry))) + continue; + page = __read_swap_cache_async(entry, gfp_mask, vma, + vmf->address, &page_allocated); + if (!page) + continue; + if (page_allocated) { + swap_readpage(page, false, &splug); + if (i != ra_info.offset) { + SetPageReadahead(page); + count_vm_event(SWAP_RA); + } + } + put_page(page); + } + blk_finish_plug(&plug); + swap_read_unplug(splug); + lru_add_drain(); +skip: + /* The page was likely read above, so no need for plugging here */ + return read_swap_cache_async(fentry, gfp_mask, vma, vmf->address, + ra_info.win == 1, NULL); +} + +/** + * swapin_readahead - swap in pages in hope we need them soon + * @entry: swap entry of this memory + * @gfp_mask: memory allocation flags + * @vmf: fault information + * + * Returns the struct page for entry and addr, after queueing swapin. + * + * It's a main entry function for swap readahead. By the configuration, + * it will read ahead blocks by cluster-based(ie, physical disk based) + * or vma-based(ie, virtual address based on faulty address) readahead. + */ +struct page *swapin_readahead(swp_entry_t entry, gfp_t gfp_mask, + struct vm_fault *vmf) +{ + return swap_use_vma_readahead() ? + swap_vma_readahead(entry, gfp_mask, vmf) : + swap_cluster_readahead(entry, gfp_mask, vmf); +} + +#ifdef CONFIG_SYSFS +static ssize_t vma_ra_enabled_show(struct kobject *kobj, + struct kobj_attribute *attr, char *buf) +{ + return sysfs_emit(buf, "%s\n", + enable_vma_readahead ? "true" : "false"); +} +static ssize_t vma_ra_enabled_store(struct kobject *kobj, + struct kobj_attribute *attr, + const char *buf, size_t count) +{ + ssize_t ret; + + ret = kstrtobool(buf, &enable_vma_readahead); + if (ret) + return ret; + + return count; +} +static struct kobj_attribute vma_ra_enabled_attr = __ATTR_RW(vma_ra_enabled); + +static struct attribute *swap_attrs[] = { + &vma_ra_enabled_attr.attr, + NULL, +}; + +static const struct attribute_group swap_attr_group = { + .attrs = swap_attrs, +}; + +static int __init swap_init_sysfs(void) +{ + int err; + struct kobject *swap_kobj; + + swap_kobj = kobject_create_and_add("swap", mm_kobj); + if (!swap_kobj) { + pr_err("failed to create swap kobject\n"); + return -ENOMEM; + } + err = sysfs_create_group(swap_kobj, &swap_attr_group); + if (err) { + pr_err("failed to register swap group\n"); + goto delete_obj; + } + return 0; + +delete_obj: + kobject_put(swap_kobj); + return err; +} +subsys_initcall(swap_init_sysfs); +#endif |