Merge tag 'hardening-v6.14-rc2' of git://git.kernel.org/pub/scm/linux/kernel/git...

[linux-stable.git] / mm / swap_state.c

// 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/mempolicy.h>
#include <linux/swap.h>
#include <linux/swapops.h>
#include <linux/init.h>
#include <linux/pagemap.h>
#include <linux/pagevec.h>
#include <linux/backing-dev.h>
#include <linux/blkdev.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_folio_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_ORDER_CEILING   5

#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", K(get_nr_swap_pages()));
        printk("Total swap = %lukB\n", K(total_swap_pages));
}

void *get_shadow_from_swap_cache(swp_entry_t entry)
{
        struct address_space *address_space = swap_address_space(entry);
        pgoff_t idx = swap_cache_index(entry);
        void *shadow;

        shadow = xa_load(&address_space->i_pages, idx);
        if (xa_is_value(shadow))
                return shadow;
        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 = swap_cache_index(entry);
        XA_STATE_ORDER(xas, &address_space->i_pages, idx, folio_order(folio));
        unsigned long i, nr = folio_nr_pages(folio);
        void *old;

        xas_set_update(&xas, workingset_update_node);

        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);
        folio->swap = entry;

        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);
                        if (shadowp) {
                                old = xas_load(&xas);
                                if (xa_is_value(old))
                                        *shadowp = old;
                        }
                        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 = swap_cache_index(entry);
        XA_STATE(xas, &address_space->i_pages, idx);

        xas_set_update(&xas, workingset_update_node);

        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);
                xas_next(&xas);
        }
        folio->swap.val = 0;
        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;
        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);
                unsigned long index = curr & SWAP_ADDRESS_SPACE_MASK;
                struct address_space *address_space = swap_address_space(entry);
                XA_STATE(xas, &address_space->i_pages, index);

                xas_set_update(&xas, workingset_update_node);

                xa_lock_irq(&address_space->i_pages);
                xas_for_each(&xas, old, min(index + (end - curr), SWAP_ADDRESS_SPACE_PAGES)) {
                        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 folio *folio)
{
        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)
{
        struct folio *folio = page_folio(page);

        free_swap_cache(folio);
        if (!is_huge_zero_folio(folio))
                folio_put(folio);
}

/*
 * 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 encoded_page **pages, int nr)
{
        struct folio_batch folios;
        unsigned int refs[PAGEVEC_SIZE];

        folio_batch_init(&folios);
        for (int i = 0; i < nr; i++) {
                struct folio *folio = page_folio(encoded_page_ptr(pages[i]));

                free_swap_cache(folio);
                refs[folios.nr] = 1;
                if (unlikely(encoded_page_flags(pages[i]) &
                             ENCODED_PAGE_BIT_NR_PAGES_NEXT))
                        refs[folios.nr] = encoded_nr_pages(pages[++i]);

                if (folio_batch_add(&folios, folio) == 0)
                        folios_put_refs(&folios, refs);
        }
        if (folios.nr)
                folios_put_refs(&folios, refs);
}

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.
 *
 * Caller must lock the swap device or hold a reference to keep it valid.
 */
struct folio *swap_cache_get_folio(swp_entry_t entry,
                struct vm_area_struct *vma, unsigned long addr)
{
        struct folio *folio;

        folio = filemap_get_folio(swap_address_space(entry), swap_cache_index(entry));
        if (!IS_ERR(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);
                }
        } else {
                folio = NULL;
        }

        return folio;
}

/**
 * filemap_get_incore_folio - Find and get a folio from the page or swap caches.
 * @mapping: The address_space to search.
 * @index: The page cache index.
 *
 * This differs from filemap_get_folio() in that it will also look for the
 * folio in the swap cache.
 *
 * Return: The found folio or %NULL.
 */
struct folio *filemap_get_incore_folio(struct address_space *mapping,
                pgoff_t index)
{
        swp_entry_t swp;
        struct swap_info_struct *si;
        struct folio *folio = filemap_get_entry(mapping, index);

        if (!folio)
                return ERR_PTR(-ENOENT);
        if (!xa_is_value(folio))
                return folio;
        if (!shmem_mapping(mapping))
                return ERR_PTR(-ENOENT);

        swp = radix_to_swp_entry(folio);
        /* There might be swapin error entries in shmem mapping. */
        if (non_swap_entry(swp))
                return ERR_PTR(-ENOENT);
        /* Prevent swapoff from happening to us */
        si = get_swap_device(swp);
        if (!si)
                return ERR_PTR(-ENOENT);
        index = swap_cache_index(swp);
        folio = filemap_get_folio(swap_address_space(swp), index);
        put_swap_device(si);
        return folio;
}

struct folio *__read_swap_cache_async(swp_entry_t entry, gfp_t gfp_mask,
                struct mempolicy *mpol, pgoff_t ilx, bool *new_page_allocated,
                bool skip_if_exists)
{
        struct swap_info_struct *si;
        struct folio *folio;
        struct folio *new_folio = NULL;
        struct folio *result = NULL;
        void *shadow = NULL;

        *new_page_allocated = false;
        si = get_swap_device(entry);
        if (!si)
                return NULL;

        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.
                 */
                folio = filemap_get_folio(swap_address_space(entry),
                                          swap_cache_index(entry));
                if (!IS_ERR(folio))
                        goto got_folio;

                /*
                 * 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 (!swap_swapcount(si, entry) && swap_slot_cache_enabled)
                        goto put_and_return;

                /*
                 * Get a new folio to read into from swap.  Allocate it now if
                 * new_folio not exist, before marking swap_map SWAP_HAS_CACHE,
                 * when -EEXIST will cause any racers to loop around until we
                 * add it to cache.
                 */
                if (!new_folio) {
                        new_folio = folio_alloc_mpol(gfp_mask, 0, mpol, ilx, numa_node_id());
                        if (!new_folio)
                                goto put_and_return;
                }

                /*
                 * Swap entry may have been freed since our caller observed it.
                 */
                err = swapcache_prepare(entry, 1);
                if (!err)
                        break;
                else if (err != -EEXIST)
                        goto put_and_return;

                /*
                 * Protect against a recursive call to __read_swap_cache_async()
                 * on the same entry waiting forever here because SWAP_HAS_CACHE
                 * is set but the folio is not the swap cache yet. This can
                 * happen today if mem_cgroup_swapin_charge_folio() below
                 * triggers reclaim through zswap, which may call
                 * __read_swap_cache_async() in the writeback path.
                 */
                if (skip_if_exists)
                        goto put_and_return;

                /*
                 * 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 folio to swap cache.
                 */
                schedule_timeout_uninterruptible(1);
        }

        /*
         * The swap entry is ours to swap in. Prepare the new folio.
         */
        __folio_set_locked(new_folio);
        __folio_set_swapbacked(new_folio);

        if (mem_cgroup_swapin_charge_folio(new_folio, NULL, gfp_mask, entry))
                goto fail_unlock;

        /* May fail (-ENOMEM) if XArray node allocation failed. */
        if (add_to_swap_cache(new_folio, entry, gfp_mask & GFP_RECLAIM_MASK, &shadow))
                goto fail_unlock;

        mem_cgroup_swapin_uncharge_swap(entry, 1);

        if (shadow)
                workingset_refault(new_folio, shadow);

        /* Caller will initiate read into locked new_folio */
        folio_add_lru(new_folio);
        *new_page_allocated = true;
        folio = new_folio;
got_folio:
        result = folio;
        goto put_and_return;

fail_unlock:
        put_swap_folio(new_folio, entry);
        folio_unlock(new_folio);
put_and_return:
        put_swap_device(si);
        if (!(*new_page_allocated) && new_folio)
                folio_put(new_folio);
        return result;
}

/*
 * 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.
 *
 * get/put_swap_device() aren't needed to call this function, because
 * __read_swap_cache_async() call them and swap_read_folio() holds the
 * swap cache folio lock.
 */
struct folio *read_swap_cache_async(swp_entry_t entry, gfp_t gfp_mask,
                struct vm_area_struct *vma, unsigned long addr,
                struct swap_iocb **plug)
{
        bool page_allocated;
        struct mempolicy *mpol;
        pgoff_t ilx;
        struct folio *folio;

        mpol = get_vma_policy(vma, addr, 0, &ilx);
        folio = __read_swap_cache_async(entry, gfp_mask, mpol, ilx,
                                        &page_allocated, false);
        mpol_cond_put(mpol);

        if (page_allocated)
                swap_read_folio(folio, plug);
        return folio;
}

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
 * @mpol: NUMA memory allocation policy to be applied
 * @ilx: NUMA interleave index, for use only when MPOL_INTERLEAVE
 *
 * Returns the struct folio 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...
 *
 * Note: it is intentional that the same NUMA policy and interleave index
 * are used for every page of the readahead: neighbouring pages on swap
 * are fairly likely to have been swapped out from the same node.
 */
struct folio *swap_cluster_readahead(swp_entry_t entry, gfp_t gfp_mask,
                                    struct mempolicy *mpol, pgoff_t ilx)
{
        struct folio *folio;
        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 page_allocated;

        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++;
        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 */
                folio = __read_swap_cache_async(
                                swp_entry(swp_type(entry), offset),
                                gfp_mask, mpol, ilx, &page_allocated, false);
                if (!folio)
                        continue;
                if (page_allocated) {
                        swap_read_folio(folio, &splug);
                        if (offset != entry_offset) {
                                folio_set_readahead(folio);
                                count_vm_event(SWAP_RA);
                        }
                }
                folio_put(folio);
        }
        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 */
        folio = __read_swap_cache_async(entry, gfp_mask, mpol, ilx,
                                        &page_allocated, false);
        if (unlikely(page_allocated))
                swap_read_folio(folio, NULL);
        return folio;
}

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 int swap_vma_ra_win(struct vm_fault *vmf, unsigned long *start,
                           unsigned long *end)
{
        struct vm_area_struct *vma = vmf->vma;
        unsigned long ra_val;
        unsigned long faddr, prev_faddr, left, right;
        unsigned int max_win, hits, prev_win, win;

        max_win = 1 << min(READ_ONCE(page_cluster), SWAP_RA_ORDER_CEILING);
        if (max_win == 1)
                return 1;

        faddr = vmf->address;
        ra_val = GET_SWAP_RA_VAL(vma);
        prev_faddr = SWAP_RA_ADDR(ra_val);
        prev_win = SWAP_RA_WIN(ra_val);
        hits = SWAP_RA_HITS(ra_val);
        win = __swapin_nr_pages(PFN_DOWN(prev_faddr), PFN_DOWN(faddr), hits,
                                max_win, prev_win);
        atomic_long_set(&vma->swap_readahead_info, SWAP_RA_VAL(faddr, win, 0));
        if (win == 1)
                return 1;

        if (faddr == prev_faddr + PAGE_SIZE)
                left = faddr;
        else if (prev_faddr == faddr + PAGE_SIZE)
                left = faddr - (win << PAGE_SHIFT) + PAGE_SIZE;
        else
                left = faddr - (((win - 1) / 2) << PAGE_SHIFT);
        right = left + (win << PAGE_SHIFT);
        if ((long)left < 0)
                left = 0;
        *start = max3(left, vma->vm_start, faddr & PMD_MASK);
        *end = min3(right, vma->vm_end, (faddr & PMD_MASK) + PMD_SIZE);

        return win;
}

/**
 * swap_vma_readahead - swap in pages in hope we need them soon
 * @targ_entry: swap entry of the targeted memory
 * @gfp_mask: memory allocation flags
 * @mpol: NUMA memory allocation policy to be applied
 * @targ_ilx: NUMA interleave index, for use only when MPOL_INTERLEAVE
 * @vmf: fault information
 *
 * Returns the struct folio 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 folio *swap_vma_readahead(swp_entry_t targ_entry, gfp_t gfp_mask,
                struct mempolicy *mpol, pgoff_t targ_ilx, struct vm_fault *vmf)
{
        struct blk_plug plug;
        struct swap_iocb *splug = NULL;
        struct folio *folio;
        pte_t *pte = NULL, pentry;
        int win;
        unsigned long start, end, addr;
        swp_entry_t entry;
        pgoff_t ilx;
        bool page_allocated;

        win = swap_vma_ra_win(vmf, &start, &end);
        if (win == 1)
                goto skip;

        ilx = targ_ilx - PFN_DOWN(vmf->address - start);

        blk_start_plug(&plug);
        for (addr = start; addr < end; ilx++, addr += PAGE_SIZE) {
                if (!pte++) {
                        pte = pte_offset_map(vmf->pmd, addr);
                        if (!pte)
                                break;
                }
                pentry = ptep_get_lockless(pte);
                if (!is_swap_pte(pentry))
                        continue;
                entry = pte_to_swp_entry(pentry);
                if (unlikely(non_swap_entry(entry)))
                        continue;
                pte_unmap(pte);
                pte = NULL;
                folio = __read_swap_cache_async(entry, gfp_mask, mpol, ilx,
                                                &page_allocated, false);
                if (!folio)
                        continue;
                if (page_allocated) {
                        swap_read_folio(folio, &splug);
                        if (addr != vmf->address) {
                                folio_set_readahead(folio);
                                count_vm_event(SWAP_RA);
                        }
                }
                folio_put(folio);
        }
        if (pte)
                pte_unmap(pte);
        blk_finish_plug(&plug);
        swap_read_unplug(splug);
        lru_add_drain();
skip:
        /* The folio was likely read above, so no need for plugging here */
        folio = __read_swap_cache_async(targ_entry, gfp_mask, mpol, targ_ilx,
                                        &page_allocated, false);
        if (unlikely(page_allocated))
                swap_read_folio(folio, NULL);
        return folio;
}

/**
 * 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 folio 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 folio *swapin_readahead(swp_entry_t entry, gfp_t gfp_mask,
                                struct vm_fault *vmf)
{
        struct mempolicy *mpol;
        pgoff_t ilx;
        struct folio *folio;

        mpol = get_vma_policy(vmf->vma, vmf->address, 0, &ilx);
        folio = swap_use_vma_readahead() ?
                swap_vma_readahead(entry, gfp_mask, mpol, ilx, vmf) :
                swap_cluster_readahead(entry, gfp_mask, mpol, ilx);
        mpol_cond_put(mpol);

        return folio;
}

#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", str_true_false(enable_vma_readahead));
}
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