diff options
Diffstat (limited to 'mm/swap_state.c')
| -rw-r--r-- | mm/swap_state.c | 1087 |
1 files changed, 1087 insertions, 0 deletions
diff --git a/mm/swap_state.c b/mm/swap_state.c new file mode 100644 index 000000000..2606504e5 --- /dev/null +++ b/mm/swap_state.c @@ -0,0 +1,1087 @@ +// 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/leafops.h> +#include <linux/init.h> +#include <linux/pagemap.h> +#include <linux/folio_batch.h> +#include <linux/backing-dev.h> +#include <linux/blk_plug.h> +#include <linux/migrate.h> +#include <linux/vmalloc.h> +#include <linux/huge_mm.h> +#include <linux/shmem_fs.h> +#include <linux/sysctl.h> +#include "internal.h" +#include "swap_table.h" +#include "swap.h" + +/* Swap readahead cluster size, as a power of 2 pages. */ +static int page_cluster; +static const int page_cluster_max = 31; + +/* + * swapper_space is a fiction, retained to simplify the path through + * vmscan's shrink_folio_list. + */ +static const struct address_space_operations swap_aops = { + .dirty_folio = noop_dirty_folio, +#ifdef CONFIG_MIGRATION + .migrate_folio = migrate_folio, +#endif +}; + +struct address_space swap_space __read_mostly = { + .a_ops = &swap_aops, +}; + +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)); +} + +/** + * swap_cache_get_folio - Looks up a folio in the swap cache. + * @entry: swap entry used for the lookup. + * + * A found folio will be returned unlocked and with its refcount increased. + * + * Context: Caller must ensure @entry is valid and protect the swap device + * with reference count or locks. + * Return: Returns the found folio on success, NULL otherwise. The caller + * must lock and check if the folio still matches the swap entry before + * use (e.g., folio_matches_swap_entry). + */ +struct folio *swap_cache_get_folio(swp_entry_t entry) +{ + unsigned long swp_tb; + struct folio *folio; + + for (;;) { + swp_tb = swap_table_get(__swap_entry_to_cluster(entry), + swp_cluster_offset(entry)); + if (!swp_tb_is_folio(swp_tb)) + return NULL; + folio = swp_tb_to_folio(swp_tb); + if (likely(folio_try_get(folio))) + return folio; + } + + return NULL; +} + +/** + * swap_cache_has_folio - Check if a swap slot has cache. + * @entry: swap entry indicating the slot. + * + * Context: Caller must ensure @entry is valid and protect the swap + * device with reference count or locks. + */ +bool swap_cache_has_folio(swp_entry_t entry) +{ + unsigned long swp_tb; + + swp_tb = swap_table_get(__swap_entry_to_cluster(entry), + swp_cluster_offset(entry)); + return swp_tb_is_folio(swp_tb); +} + +/** + * swap_cache_get_shadow - Looks up a shadow in the swap cache. + * @entry: swap entry used for the lookup. + * + * Context: Caller must ensure @entry is valid and protect the swap device + * with reference count or locks. + * Return: Returns either NULL or an XA_VALUE (shadow). + */ +void *swap_cache_get_shadow(swp_entry_t entry) +{ + unsigned long swp_tb; + + swp_tb = swap_table_get(__swap_entry_to_cluster(entry), + swp_cluster_offset(entry)); + if (swp_tb_is_shadow(swp_tb)) + return swp_tb_to_shadow(swp_tb); + return NULL; +} + +/** + * __swap_cache_add_check - Check if a range is suitable for adding a folio. + * @ci: The locked swap cluster + * @targ_entry: The target swap entry to check, will be rounded down by @nr + * @nr: Number of slots to check, must be a power of 2 + * @shadowp: Returns the shadow value if one exists in the range + * @memcg_id: Returns the memory cgroup id, NULL to ignore cgroup check + * + * Check if all slots covered by given range have a swap count >= 1. + * Retrieves the shadow if there is one. If @memcg_id is not NULL, also + * checks if all slots belong to the same cgroup and return the cgroup + * private id. + * + * Context: Caller must lock the cluster. + * Return: 0 if success, error code if failed. + */ +static int __swap_cache_add_check(struct swap_cluster_info *ci, + swp_entry_t targ_entry, + unsigned long nr, void **shadowp, + unsigned short *memcg_id) +{ + unsigned int ci_off, ci_end; + unsigned long old_tb; + bool is_zero; + + lockdep_assert_held(&ci->lock); + + /* + * If the target slot is not swapped out or already cached, return + * -ENOENT or -EEXIST. If the batch is not suitable, could be a + * race with concurrent free or cache add, return -EBUSY. + */ + if (unlikely(!ci->table)) + return -ENOENT; + ci_off = swp_cluster_offset(targ_entry); + old_tb = __swap_table_get(ci, ci_off); + if (swp_tb_is_folio(old_tb)) + return -EEXIST; + if (!__swp_tb_get_count(old_tb)) + return -ENOENT; + if (shadowp && swp_tb_is_shadow(old_tb)) + *shadowp = swp_tb_to_shadow(old_tb); + if (memcg_id) + *memcg_id = __swap_cgroup_get(ci, ci_off); + + if (nr == 1) + return 0; + + is_zero = __swap_table_test_zero(ci, ci_off); + ci_off = round_down(ci_off, nr); + ci_end = ci_off + nr; + do { + old_tb = __swap_table_get(ci, ci_off); + if (unlikely(swp_tb_is_folio(old_tb) || + !__swp_tb_get_count(old_tb) || + is_zero != __swap_table_test_zero(ci, ci_off) || + (memcg_id && *memcg_id != __swap_cgroup_get(ci, ci_off)))) + return -EBUSY; + } while (++ci_off < ci_end); + + return 0; +} + +static void __swap_cache_do_add_folio(struct swap_cluster_info *ci, + struct folio *folio, swp_entry_t entry) +{ + unsigned int ci_off = swp_cluster_offset(entry), ci_end; + unsigned long nr_pages = folio_nr_pages(folio); + unsigned long pfn = folio_pfn(folio); + unsigned long old_tb; + + VM_WARN_ON_ONCE_FOLIO(!folio_test_locked(folio), folio); + VM_WARN_ON_ONCE_FOLIO(folio_test_swapcache(folio), folio); + VM_WARN_ON_ONCE_FOLIO(!folio_test_swapbacked(folio), folio); + + ci_end = ci_off + nr_pages; + do { + old_tb = __swap_table_get(ci, ci_off); + VM_WARN_ON_ONCE(swp_tb_is_folio(old_tb)); + __swap_table_set(ci, ci_off, pfn_to_swp_tb(pfn, __swp_tb_get_flags(old_tb))); + } while (++ci_off < ci_end); + + folio_ref_add(folio, nr_pages); + folio_set_swapcache(folio); + folio->swap = entry; +} + +/** + * __swap_cache_add_folio - Add a folio to the swap cache and update stats. + * @ci: The locked swap cluster. + * @folio: The folio to be added. + * @entry: The swap entry corresponding to the folio. + * + * Unconditionally add a folio to the swap cache. The caller must ensure + * all slots are usable and have no conflicts. This assigns entry to + * @folio->swap, increases folio refcount by the number of pages, and + * updates swap cache stats. + * + * Context: Caller must ensure the folio is locked and lock the cluster + * that holds the entries. + */ +void __swap_cache_add_folio(struct swap_cluster_info *ci, + struct folio *folio, swp_entry_t entry) +{ + unsigned long nr_pages = folio_nr_pages(folio); + + __swap_cache_do_add_folio(ci, folio, entry); + node_stat_mod_folio(folio, NR_FILE_PAGES, nr_pages); + lruvec_stat_mod_folio(folio, NR_SWAPCACHE, nr_pages); +} + +static void __swap_cache_do_del_folio(struct swap_cluster_info *ci, + struct folio *folio, + swp_entry_t entry, void *shadow) +{ + unsigned long old_tb; + struct swap_info_struct *si; + unsigned int ci_start, ci_off, ci_end; + bool folio_swapped = false, need_free = false; + unsigned long nr_pages = folio_nr_pages(folio); + + VM_WARN_ON_ONCE(__swap_entry_to_cluster(entry) != ci); + VM_WARN_ON_ONCE_FOLIO(!folio_test_locked(folio), folio); + VM_WARN_ON_ONCE_FOLIO(!folio_test_swapcache(folio), folio); + VM_WARN_ON_ONCE_FOLIO(folio_test_writeback(folio), folio); + + si = __swap_entry_to_info(entry); + ci_start = swp_cluster_offset(entry); + ci_end = ci_start + nr_pages; + ci_off = ci_start; + do { + old_tb = __swap_table_get(ci, ci_off); + WARN_ON_ONCE(!swp_tb_is_folio(old_tb) || + swp_tb_to_folio(old_tb) != folio); + if (__swp_tb_get_count(old_tb)) + folio_swapped = true; + else + need_free = true; + /* If shadow is NULL, we set an empty shadow. */ + __swap_table_set(ci, ci_off, shadow_to_swp_tb(shadow, + __swp_tb_get_flags(old_tb))); + } while (++ci_off < ci_end); + + folio->swap.val = 0; + folio_clear_swapcache(folio); + + if (!folio_swapped) { + __swap_cluster_free_entries(si, ci, ci_start, nr_pages); + } else if (need_free) { + ci_off = ci_start; + do { + if (!__swp_tb_get_count(__swap_table_get(ci, ci_off))) + __swap_cluster_free_entries(si, ci, ci_off, 1); + } while (++ci_off < ci_end); + } +} + +/** + * __swap_cache_del_folio - Removes a folio from the swap cache. + * @ci: The locked swap cluster. + * @folio: The folio. + * @entry: The first swap entry that the folio corresponds to. + * @shadow: shadow value to be filled in the swap cache. + * + * Removes a folio from the swap cache and fills a shadow in place. + * This won't put the folio's refcount. The caller has to do that. + * + * Context: Caller must ensure the folio is locked and in the swap cache + * using the index of @entry, and lock the cluster that holds the entries. + */ +void __swap_cache_del_folio(struct swap_cluster_info *ci, struct folio *folio, + swp_entry_t entry, void *shadow) +{ + unsigned long nr_pages = folio_nr_pages(folio); + + __swap_cache_do_del_folio(ci, folio, entry, shadow); + node_stat_mod_folio(folio, NR_FILE_PAGES, -nr_pages); + lruvec_stat_mod_folio(folio, NR_SWAPCACHE, -nr_pages); +} + +/** + * swap_cache_del_folio - Removes a folio from the swap cache. + * @folio: The folio. + * + * Same as __swap_cache_del_folio, but handles lock and refcount. The + * caller must ensure the folio is either clean or has a swap count + * equal to zero, or it may cause data loss. + * + * Context: Caller must ensure the folio is locked and in the swap cache. + */ +void swap_cache_del_folio(struct folio *folio) +{ + struct swap_cluster_info *ci; + swp_entry_t entry = folio->swap; + + ci = swap_cluster_lock(__swap_entry_to_info(entry), swp_offset(entry)); + __swap_cache_del_folio(ci, folio, entry, NULL); + swap_cluster_unlock(ci); + + folio_ref_sub(folio, folio_nr_pages(folio)); +} + +/** + * __swap_cache_replace_folio - Replace a folio in the swap cache. + * @ci: The locked swap cluster. + * @old: The old folio to be replaced. + * @new: The new folio. + * + * Replace an existing folio in the swap cache with a new folio. The + * caller is responsible for setting up the new folio's flag and swap + * entries. Replacement will take the new folio's swap entry value as + * the starting offset to override all slots covered by the new folio. + * + * Context: Caller must ensure both folios are locked, and lock the + * cluster that holds the old folio to be replaced. + */ +void __swap_cache_replace_folio(struct swap_cluster_info *ci, + struct folio *old, struct folio *new) +{ + swp_entry_t entry = new->swap; + unsigned long nr_pages = folio_nr_pages(new); + unsigned int ci_off = swp_cluster_offset(entry); + unsigned int ci_end = ci_off + nr_pages; + unsigned long pfn = folio_pfn(new); + unsigned long old_tb; + + VM_WARN_ON_ONCE(!folio_test_swapcache(old) || !folio_test_swapcache(new)); + VM_WARN_ON_ONCE(!folio_test_locked(old) || !folio_test_locked(new)); + VM_WARN_ON_ONCE(!entry.val); + + /* Swap cache still stores N entries instead of a high-order entry */ + do { + old_tb = __swap_table_get(ci, ci_off); + WARN_ON_ONCE(!swp_tb_is_folio(old_tb) || swp_tb_to_folio(old_tb) != old); + __swap_table_set(ci, ci_off, pfn_to_swp_tb(pfn, __swp_tb_get_flags(old_tb))); + } while (++ci_off < ci_end); + + /* + * If the old folio is partially replaced (e.g., splitting a large + * folio, the old folio is shrunk, and new split sub folios replace + * the shrunk part), ensure the new folio doesn't overlap it. + */ + if (IS_ENABLED(CONFIG_DEBUG_VM) && + folio_order(old) != folio_order(new)) { + ci_off = swp_cluster_offset(old->swap); + ci_end = ci_off + folio_nr_pages(old); + while (ci_off++ < ci_end) + WARN_ON_ONCE(swp_tb_to_folio(__swap_table_get(ci, ci_off)) != old); + } +} + +/* + * Try to allocate a folio of given order in the swap cache. + * + * This helper resolves the potential races of swap allocation + * and prepares a folio to be used for swap IO. May return following + * value: + * + * -ENOMEM / -EBUSY: Order is too large or in conflict with sub slot, + * caller should shrink the order and retry + * -ENOENT / -EEXIST: Target swap entry is unavailable or cached, the caller + * should abort or try to use the cached folio instead + */ +static struct folio *__swap_cache_alloc(struct swap_cluster_info *ci, + swp_entry_t targ_entry, gfp_t gfp, + unsigned int order, struct vm_fault *vmf, + struct mempolicy *mpol, pgoff_t ilx) +{ + int err; + swp_entry_t entry; + struct folio *folio; + void *shadow = NULL; + unsigned short memcg_id; + unsigned long address, nr_pages = 1UL << order; + struct vm_area_struct *vma = vmf ? vmf->vma : NULL; + + VM_WARN_ON_ONCE(nr_pages > SWAPFILE_CLUSTER); + entry.val = round_down(targ_entry.val, nr_pages); + + /* Check if the slot and range are available, skip allocation if not */ + spin_lock(&ci->lock); + err = __swap_cache_add_check(ci, targ_entry, nr_pages, NULL, NULL); + spin_unlock(&ci->lock); + if (unlikely(err)) + return ERR_PTR(err); + + /* + * Limit THP gfp. The limitation is a no-op for typical + * GFP_HIGHUSER_MOVABLE but matters for shmem. + */ + if (order) + gfp = thp_shmem_limit_gfp_mask(vma_thp_gfp_mask(vma), gfp); + + if (mpol || !vmf) { + folio = folio_alloc_mpol(gfp, order, mpol, ilx, numa_node_id()); + } else { + address = round_down(vmf->address, PAGE_SIZE << order); + folio = vma_alloc_folio(gfp, order, vmf->vma, address); + } + if (unlikely(!folio)) + return ERR_PTR(-ENOMEM); + + /* Double check the range is still not in conflict */ + spin_lock(&ci->lock); + err = __swap_cache_add_check(ci, targ_entry, nr_pages, &shadow, &memcg_id); + if (unlikely(err)) { + spin_unlock(&ci->lock); + folio_put(folio); + return ERR_PTR(err); + } + + __folio_set_locked(folio); + __folio_set_swapbacked(folio); + __swap_cache_do_add_folio(ci, folio, entry); + spin_unlock(&ci->lock); + + if (mem_cgroup_swapin_charge_folio(folio, memcg_id, + vmf ? vmf->vma->vm_mm : NULL, gfp)) { + spin_lock(&ci->lock); + __swap_cache_do_del_folio(ci, folio, entry, shadow); + spin_unlock(&ci->lock); + folio_unlock(folio); + /* nr_pages refs from swap cache, 1 from allocation */ + folio_put_refs(folio, nr_pages + 1); + count_mthp_stat(order, MTHP_STAT_SWPIN_FALLBACK_CHARGE); + return ERR_PTR(-ENOMEM); + } + + if (order > 1 && folio_memcg_alloc_deferred(folio)) { + spin_lock(&ci->lock); + __swap_cache_do_del_folio(ci, folio, entry, shadow); + spin_unlock(&ci->lock); + folio_unlock(folio); + /* nr_pages refs from swap cache, 1 from allocation */ + folio_put_refs(folio, nr_pages + 1); + return ERR_PTR(-ENOMEM); + } + + /* memsw uncharges swap when folio is added to swap cache */ + memcg1_swapin(folio); + if (shadow) + workingset_refault(folio, shadow); + + node_stat_mod_folio(folio, NR_FILE_PAGES, nr_pages); + lruvec_stat_mod_folio(folio, NR_SWAPCACHE, nr_pages); + + /* Caller will initiate read into locked new_folio */ + folio_add_lru(folio); + return folio; +} + +/** + * swap_cache_alloc_folio - Allocate folio for swapped out slot in swap cache. + * @targ_entry: swap entry indicating the target slot + * @gfp: memory allocation flags + * @orders: allocation orders, must be non zero + * @vmf: fault information + * @mpol: NUMA memory allocation policy to be applied + * @ilx: NUMA interleave index, for use only when MPOL_INTERLEAVE + * + * Allocate a folio in the swap cache for one swap slot, typically before + * doing IO (e.g. swap in or zswap writeback). The swap slot indicated by + * @targ_entry must have a non-zero swap count (swapped out). + * + * Context: Caller must protect the swap device with reference count or locks. + * Return: Returns the folio if allocation succeeded and folio is in the swap + * cache. Returns error code if failed due to race, OOM or invalid arguments. + */ +struct folio *swap_cache_alloc_folio(swp_entry_t targ_entry, gfp_t gfp, + unsigned long orders, struct vm_fault *vmf, + struct mempolicy *mpol, pgoff_t ilx) +{ + int order, err; + struct folio *ret; + struct swap_cluster_info *ci; + + ci = __swap_entry_to_cluster(targ_entry); + order = highest_order(orders); + + /* orders must be non-zero, and must not exceed cluster size. */ + if (WARN_ON_ONCE(!orders || (1UL << order) > SWAPFILE_CLUSTER)) + return ERR_PTR(-EINVAL); + + do { + ret = __swap_cache_alloc(ci, targ_entry, gfp, order, + vmf, mpol, ilx); + if (!IS_ERR(ret)) + break; + err = PTR_ERR(ret); + if (!order || (err && err != -EBUSY && err != -ENOMEM)) + break; + count_mthp_stat(order, MTHP_STAT_SWPIN_FALLBACK); + order = next_order(&orders, order); + } while (orders); + + return ret; +} + +/* + * 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); + } +} + +/* + * Freeing a folio and also freeing any swap cache associated with + * this folio if it is the last user. + */ +void free_folio_and_swap_cache(struct folio *folio) +{ + 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[FOLIO_BATCH_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); +} + +/** + * swap_update_readahead - Update the readahead statistics of VMA or globally. + * @folio: the swap cache folio that just got hit. + * @vma: the VMA that should be updated, could be NULL for global update. + * @addr: the addr that triggered the swapin, ignored if @vma is NULL. + */ +void swap_update_readahead(struct folio *folio, struct vm_area_struct *vma, + unsigned long addr) +{ + bool readahead, vma_ra = swap_use_vma_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; + + 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); + } +} + +static struct folio *swap_cache_read_folio(swp_entry_t entry, gfp_t gfp, + struct mempolicy *mpol, pgoff_t ilx, + struct swap_iocb **plug, bool readahead) +{ + struct folio *folio; + + do { + folio = swap_cache_get_folio(entry); + if (folio) + return folio; + folio = swap_cache_alloc_folio(entry, gfp, BIT(0), NULL, mpol, ilx); + } while (PTR_ERR(folio) == -EEXIST); + + if (IS_ERR_OR_NULL(folio)) + return NULL; + + swap_read_folio(folio, plug); + if (readahead) { + folio_set_readahead(folio); + count_vm_event(SWAP_RA); + } + + return folio; +} + +/** + * swapin_sync - swap-in one or multiple entries skipping readahead. + * @entry: swap entry indicating the target slot + * @gfp: memory allocation flags + * @orders: allocation orders + * @vmf: fault information + * @mpol: NUMA memory allocation policy to be applied + * @ilx: NUMA interleave index, for use only when MPOL_INTERLEAVE + * + * This allocates a folio suitable for given @orders, or returns the + * existing folio in the swap cache for @entry. This initiates the IO, too, + * if needed. @entry is rounded down if @orders allow large allocation. + * + * Context: Caller must ensure @entry is valid and pin the swap device with refcount. + * Return: Returns the folio on success, error code if failed. + */ +struct folio *swapin_sync(swp_entry_t entry, gfp_t gfp, unsigned long orders, + struct vm_fault *vmf, struct mempolicy *mpol, pgoff_t ilx) +{ + struct folio *folio; + + do { + folio = swap_cache_get_folio(entry); + if (folio) + return folio; + folio = swap_cache_alloc_folio(entry, gfp, orders, vmf, mpol, ilx); + } while (PTR_ERR(folio) == -EEXIST); + + if (IS_ERR(folio)) + return folio; + + swap_read_folio(folio, NULL); + return folio; +} + +/* + * 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 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) +{ + struct swap_info_struct *si; + struct mempolicy *mpol; + pgoff_t ilx; + struct folio *folio; + + si = get_swap_device(entry); + if (!si) + return NULL; + + mpol = get_vma_policy(vma, addr, 0, &ilx); + folio = swap_cache_read_folio(entry, gfp_mask, mpol, ilx, plug, false); + mpol_cond_put(mpol); + + put_swap_device(si); + 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 = __swap_entry_to_info(entry); + struct blk_plug plug; + struct swap_iocb *splug = NULL; + swp_entry_t ra_entry; + + 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 */ + ra_entry = swp_entry(swp_type(entry), offset); + folio = swap_cache_read_folio(ra_entry, gfp_mask, mpol, ilx, + &splug, offset != entry_offset); + if (!folio) + continue; + folio_put(folio); + } + blk_finish_plug(&plug); + swap_read_unplug(splug); +skip: + /* The page was likely read above, so no need for plugging here */ + return swap_cache_read_folio(entry, gfp_mask, mpol, ilx, NULL, false); +} + +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; + pgoff_t ilx = targ_ilx; + + 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) { + struct swap_info_struct *si = NULL; + softleaf_t entry; + + if (!pte++) { + pte = pte_offset_map(vmf->pmd, addr); + if (!pte) + break; + } + pentry = ptep_get_lockless(pte); + entry = softleaf_from_pte(pentry); + + if (!softleaf_is_swap(entry)) + continue; + pte_unmap(pte); + pte = NULL; + /* + * Readahead entry may come from a device that we are not + * holding a reference to, try to grab a reference, or skip. + */ + if (swp_type(entry) != swp_type(targ_entry)) { + si = get_swap_device(entry); + if (!si) + continue; + } + folio = swap_cache_read_folio(entry, gfp_mask, mpol, ilx, + &splug, addr != vmf->address); + if (si) + put_swap_device(si); + if (!folio) + continue; + folio_put(folio); + } + if (pte) + pte_unmap(pte); + blk_finish_plug(&plug); + swap_read_unplug(splug); +skip: + /* The folio was likely read above, so no need for plugging here */ + folio = swap_cache_read_folio(targ_entry, gfp_mask, mpol, targ_ilx, + NULL, false); + 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; +} + +static const struct ctl_table swap_readahead_sysctl_table[] = { + { + .procname = "page-cluster", + .data = &page_cluster, + .maxlen = sizeof(int), + .mode = 0644, + .proc_handler = proc_dointvec_minmax, + .extra1 = SYSCTL_ZERO, + .extra2 = (void *)&page_cluster_max, + } +}; + +static void __init swap_readahead_setup(void) +{ + unsigned long megs = PAGES_TO_MB(totalram_pages()); + + /* Use a smaller cluster for small-memory machines */ + if (megs < 16) + page_cluster = 2; + else + page_cluster = 3; + /* + * Right now other parts of the system means that we + * _really_ don't want to cluster much more + */ + + register_sysctl_init("vm", swap_readahead_sysctl_table); +} + +#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_sysfs_init(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; + } + /* Swap cache writeback is LRU based, no tags for it */ + mapping_set_no_writeback_tags(&swap_space); + return 0; + +delete_obj: + kobject_put(swap_kobj); + return err; +} +#else +static int __init swap_sysfs_init(void) +{ + return 0; +} +#endif + +static int __init swap_init(void) +{ + swap_readahead_setup(); + + return swap_sysfs_init(); +} +subsys_initcall(swap_init); |