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Message-ID: <aLJZ4Q1ioAiUsWv2@MiWiFi-R3L-srv>
Date: Sat, 30 Aug 2025 09:54:41 +0800
From: Baoquan He <bhe@...hat.com>
To: Kairui Song <kasong@...cent.com>
Cc: linux-mm@...ck.org, Andrew Morton <akpm@...ux-foundation.org>,
Matthew Wilcox <willy@...radead.org>,
Hugh Dickins <hughd@...gle.com>, Chris Li <chrisl@...nel.org>,
Barry Song <baohua@...nel.org>, Nhat Pham <nphamcs@...il.com>,
Kemeng Shi <shikemeng@...weicloud.com>,
Baolin Wang <baolin.wang@...ux.alibaba.com>,
Ying Huang <ying.huang@...ux.alibaba.com>,
Johannes Weiner <hannes@...xchg.org>,
David Hildenbrand <david@...hat.com>,
Yosry Ahmed <yosryahmed@...gle.com>,
Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
Zi Yan <ziy@...dia.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 6/9] mm, swap: use the swap table for the swap cache and
switch API
On 08/23/25 at 03:20am, Kairui Song wrote:
> From: Kairui Song <kasong@...cent.com>
......snip...
> diff --git a/mm/swap.h b/mm/swap.h
> index 7b3efaa51624..4af42bc2cd72 100644
> --- a/mm/swap.h
> +++ b/mm/swap.h
......snip...
> +/*
> + * All swap cache helpers below require the caller to ensure the swap entries
> + * are valid and pin the device. This can be guaranteed by:
> + * - get_swap_device: this ensures a single entry is valid and increases the
> + * swap device's refcount.
> + * - Locking a folio in the swap cache: this ensures the folio won't be freed
> + * from the swap cache, stabilizes its entries, and the swap device.
> + * - Locking anything referencing the swap entry: e.g. locking the PTL that
> + * protects swap entries in the page table, so they won't be freed.
> + */
> +extern struct folio *swap_cache_get_folio(swp_entry_t entry);
> +extern void *swap_cache_get_shadow(swp_entry_t entry);
> +extern int swap_cache_add_folio(swp_entry_t entry,
> + struct folio *folio, void **shadow);
> +extern void swap_cache_del_folio(struct folio *folio);
> +/* Below helpers also require the caller to lock the swap cluster. */
> +extern void __swap_cache_del_folio(swp_entry_t entry,
> + struct folio *folio, void *shadow);
> +extern void __swap_cache_replace_folio(struct swap_cluster_info *ci,
> + swp_entry_t entry, struct folio *old,
> + struct folio *new);
> +extern void __swap_cache_clear_shadow(swp_entry_t entry, int nr_ents);
> +
> void show_swap_cache_info(void);
> -void *get_shadow_from_swap_cache(swp_entry_t entry);
> -int add_to_swap_cache(struct folio *folio, swp_entry_t entry,
> - gfp_t gfp, void **shadowp);
> -void __delete_from_swap_cache(struct folio *folio,
> - swp_entry_t entry, void *shadow);
> -void delete_from_swap_cache(struct folio *folio);
> -void clear_shadow_from_swap_cache(int type, unsigned long begin,
> - unsigned long end);
> void swapcache_clear(struct swap_info_struct *si, swp_entry_t entry, int nr);
> -struct folio *swap_cache_get_folio(swp_entry_t entry);
> 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);
I would put this function renaming change to another standalone patch,
then let this key patch focus on swap table introducing.
> @@ -235,6 +283,33 @@ static inline int non_swapcache_batch(swp_entry_t entry, int max_nr)
>
> #else /* CONFIG_SWAP */
> struct swap_iocb;
> +
> +static inline struct swap_cluster_info *swap_cluster_lock(
> + struct swap_info_struct *si, pgoff_t offset, bool irq)
> +{
> + return NULL;
> +}
> +
> +static inline struct swap_cluster_info *swap_cluster_lock_by_folio(
> + struct folio *folio)
> +{
> + return NULL;
> +}
> +
> +static inline struct swap_cluster_info *swap_cluster_lock_by_folio_irq(
> + struct folio *folio)
> +{
> + return NULL;
> +}
> +
> +static inline void swap_cluster_unlock(struct swap_cluster_info *ci)
> +{
> +}
> +
> +static inline void swap_cluster_unlock_irq(struct swap_cluster_info *ci)
> +{
> +}
> +
> static inline struct swap_info_struct *swp_info(swp_entry_t entry)
> {
> return NULL;
> @@ -252,11 +327,6 @@ static inline struct address_space *swap_address_space(swp_entry_t entry)
> return NULL;
> }
>
> -static inline pgoff_t swap_cache_index(swp_entry_t entry)
> -{
> - return 0;
> -}
> -
> static inline bool folio_contains_swap(struct folio *folio, swp_entry_t entry)
> {
> return false;
> @@ -298,28 +368,27 @@ static inline struct folio *swap_cache_get_folio(swp_entry_t entry)
> return NULL;
> }
>
> -static inline void *get_shadow_from_swap_cache(swp_entry_t entry)
> +static inline void *swap_cache_get_shadow(swp_entry_t end)
> {
> return NULL;
> }
>
> -static inline int add_to_swap_cache(struct folio *folio, swp_entry_t entry,
> - gfp_t gfp_mask, void **shadowp)
> +static inline int swap_cache_add_folio(swp_entry_t end, struct folio *folio, void **shadow)
> {
> - return -1;
> + return -EINVAL;
> }
>
> -static inline void __delete_from_swap_cache(struct folio *folio,
> - swp_entry_t entry, void *shadow)
> +static inline void swap_cache_del_folio(struct folio *folio)
> {
> }
>
> -static inline void delete_from_swap_cache(struct folio *folio)
> +static inline void __swap_cache_del_folio(swp_entry_t entry, struct folio *folio, void *shadow)
> {
> }
>
> -static inline void clear_shadow_from_swap_cache(int type, unsigned long begin,
> - unsigned long end)
> +static inline void __swap_cache_replace_folio(
> + struct swap_cluster_info *ci, swp_entry_t entry,
> + struct folio *old, struct folio *new)
> {
> }
>
> @@ -354,7 +423,7 @@ static inline int non_swapcache_batch(swp_entry_t entry, int max_nr)
> static inline pgoff_t folio_index(struct folio *folio)
> {
> if (unlikely(folio_test_swapcache(folio)))
> - return swap_cache_index(folio->swap);
> + return swp_offset(folio->swap);
> return folio->index;
> }
>
> diff --git a/mm/swap_state.c b/mm/swap_state.c
> index 721ff1a5e73a..c0342024b4a8 100644
> --- a/mm/swap_state.c
> +++ b/mm/swap_state.c
> @@ -23,6 +23,7 @@
> #include <linux/huge_mm.h>
> #include <linux/shmem_fs.h>
> #include "internal.h"
> +#include "swap_table.h"
> #include "swap.h"
>
> /*
> @@ -36,8 +37,11 @@ static const struct address_space_operations swap_aops = {
> #endif
> };
>
> -struct address_space *swapper_spaces[MAX_SWAPFILES] __read_mostly;
> -static unsigned int nr_swapper_spaces[MAX_SWAPFILES] __read_mostly;
> +/* Set swap_space is read only as swap cache is handled by swap table */
> +struct address_space swap_space __ro_after_init = {
> + .a_ops = &swap_aops,
> +};
> +
> static bool enable_vma_readahead __read_mostly = true;
>
> #define SWAP_RA_ORDER_CEILING 5
> @@ -69,7 +73,7 @@ void show_swap_cache_info(void)
> printk("Total swap = %lukB\n", K(total_swap_pages));
> }
>
> -/*
> +/**
> * swap_cache_get_folio - Lookup a swap entry in the swap cache.
> *
> * A found folio will be returned unlocked and with its refcount increased.
> @@ -79,155 +83,179 @@ void show_swap_cache_info(void)
> */
> struct folio *swap_cache_get_folio(swp_entry_t entry)
> {
> - struct folio *folio = filemap_get_folio(swap_address_space(entry),
> - swap_cache_index(entry));
> - if (!IS_ERR(folio))
> - return folio;
> + unsigned long swp_tb;
> + struct folio *folio;
> +
> + for (;;) {
> + swp_tb = __swap_table_get(swp_cluster(entry), swp_cluster_offset(entry));
> + if (!swp_tb_is_folio(swp_tb))
> + return NULL;
> + folio = swp_tb_to_folio(swp_tb);
> + if (folio_try_get(folio))
> + return folio;
> + }
> +
> return NULL;
> }
>
> -void *get_shadow_from_swap_cache(swp_entry_t entry)
> +/**
> + * swap_cache_get_shadow - Lookup a shadow in the swap cache.
> + *
> + * Context: Caller must ensure @entry is valid and pin the swap device.
> + */
> +void *swap_cache_get_shadow(swp_entry_t entry)
> {
> - struct address_space *address_space = swap_address_space(entry);
> - pgoff_t idx = swap_cache_index(entry);
> - void *shadow;
> + unsigned long swp_tb;
> +
> + swp_tb = __swap_table_get(swp_cluster(entry), swp_cluster_offset(entry));
> + if (swp_tb_is_shadow(swp_tb))
> + return swp_tb_to_shadow(swp_tb);
>
> - 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 'swap' instead of mapping and index.
> +/**
> + * swap_cache_add_folio - add a folio into the swap cache.
> + *
> + * The folio will be used for swapin or swapout of swap entries
> + * starting with @entry. May fail due to race.
> + *
> + * Context: Caller must ensure @entry is valid and pin the swap device.
> */
> -int add_to_swap_cache(struct folio *folio, swp_entry_t entry,
> - gfp_t gfp, void **shadowp)
> +int swap_cache_add_folio(swp_entry_t entry, struct folio *folio, 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);
> + unsigned long exist;
> + void *shadow = NULL;
> + struct swap_cluster_info *ci;
> + unsigned int ci_start, ci_off, ci_end;
> + unsigned long nr_pages = folio_nr_pages(folio);
> +
> + 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 = swap_cluster_lock(swp_info(entry), swp_offset(entry));
> + ci_start = swp_cluster_offset(entry);
> + ci_end = ci_start + nr_pages;
> + ci_off = ci_start;
> + do {
> + exist = __swap_table_get(ci, ci_off);
> + if (unlikely(swp_tb_is_folio(exist)))
> + goto fail;
> + if (swp_tb_is_shadow(exist))
> + shadow = swp_tb_to_shadow(exist);
> + } while (++ci_off < ci_end);
> +
> + ci_off = ci_start;
> + do {
> + __swap_table_set_folio(ci, ci_off, folio);
> + } while (++ci_off < ci_end);
>
> - folio_ref_add(folio, nr);
> + folio_ref_add(folio, nr_pages);
> folio_set_swapcache(folio);
> folio->swap = entry;
> + swap_cluster_unlock(ci);
>
> - 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;
> + node_stat_mod_folio(folio, NR_FILE_PAGES, nr_pages);
> + lruvec_stat_mod_folio(folio, NR_SWAPCACHE, nr_pages);
>
> - folio_clear_swapcache(folio);
> - folio_ref_sub(folio, nr);
> - return xas_error(&xas);
> + if (shadowp)
> + *shadowp = shadow;
> + return 0;
> +fail:
> + swap_cluster_unlock(ci);
> + return -EEXIST;
> }
>
> /*
> - * This must be called only on folios that have
> - * been verified to be in the swap cache.
> + * Caller must ensure the folio is in the swap cache and locked,
> + * also lock the swap cluster.
> */
> -void __delete_from_swap_cache(struct folio *folio,
> - swp_entry_t entry, void *shadow)
> +void __swap_cache_del_folio(swp_entry_t entry, struct folio *folio,
> + 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);
> - }
> + unsigned long exist;
> + struct swap_cluster_info *ci;
> + unsigned int ci_start, ci_off, ci_end;
> + unsigned long nr_pages = folio_nr_pages(folio);
> +
> + 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);
> +
> + ci = swp_offset_cluster(swp_info(entry), swp_offset(entry));
> + ci_start = swp_cluster_offset(entry);
> + ci_end = ci_start + nr_pages;
> + ci_off = ci_start;
> + do {
> + exist = __swap_table_get(ci, ci_off);
> + VM_WARN_ON_ONCE(swp_tb_to_folio(exist) != folio);
> + /* If shadow is NULL, we sets an empty shadow */
> + __swap_table_set_shadow(ci, ci_off, shadow);
> + } while (++ci_off < ci_end);
> +
> 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);
> + node_stat_mod_folio(folio, NR_FILE_PAGES, -nr_pages);
> + lruvec_stat_mod_folio(folio, NR_SWAPCACHE, -nr_pages);
> }
>
> /*
> - * 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.
> + * Replace an old folio in the swap cache with a new one. The caller must
> + * hold the cluster lock and set the new folio's entry and flags.
> */
> -void delete_from_swap_cache(struct folio *folio)
> +void __swap_cache_replace_folio(struct swap_cluster_info *ci, swp_entry_t entry,
> + struct folio *old, struct folio *new)
> +{
> + unsigned int ci_off = swp_cluster_offset(entry);
> + unsigned long nr_pages = folio_nr_pages(new);
> + unsigned int ci_end = ci_off + nr_pages;
> +
> + VM_WARN_ON_ONCE(entry.val != new->swap.val);
> + VM_WARN_ON_ONCE(!folio_test_locked(old) || !folio_test_locked(new));
> + VM_WARN_ON_ONCE(!folio_test_swapcache(old) || !folio_test_swapcache(new));
> + do {
> + WARN_ON_ONCE(swp_tb_to_folio(__swap_table_get(ci, ci_off)) != old);
> + __swap_table_set_folio(ci, ci_off, new);
> + } while (++ci_off < ci_end);
> +
> + /*
> + * If the old folio is partially replaced (e.g., splitting a large
> + * folio, the old folio is shrunk in place, and new split sub folios
> + * are added to cache), 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);
> + }
> +}
> +
> +void swap_cache_del_folio(struct folio *folio)
> {
> + struct swap_cluster_info *ci;
> 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);
> + ci = swap_cluster_lock(swp_info(entry), swp_offset(entry));
> + __swap_cache_del_folio(entry, folio, NULL);
> + swap_cluster_unlock(ci);
>
> 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)
> +void __swap_cache_clear_shadow(swp_entry_t entry, int nr_ents)
> {
> - 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);
> + struct swap_cluster_info *ci = swp_cluster(entry);
> + unsigned int ci_off = swp_cluster_offset(entry), ci_end;
>
> - /* search the next swapcache until we meet end */
> - curr = ALIGN((curr + 1), SWAP_ADDRESS_SPACE_PAGES);
> - if (curr > end)
> - break;
> - }
> + ci_end = ci_off + nr_ents;
> + do {
> + WARN_ON_ONCE(swp_tb_is_folio(__swap_table_get(ci, ci_off)));
> + __swap_table_init_null(ci, ci_off);
> + } while (++ci_off < ci_end);
> }
>
> /*
> @@ -292,8 +320,7 @@ static inline bool swap_use_vma_readahead(void)
> /*
> * Update the readahead statistics of a vma or globally.
> */
> -void swap_update_readahead(struct folio *folio,
> - struct vm_area_struct *vma,
> +void swap_update_readahead(struct folio *folio, struct vm_area_struct *vma,
> unsigned long addr)
> {
> bool readahead, vma_ra = swap_use_vma_readahead();
> @@ -387,7 +414,7 @@ struct folio *__read_swap_cache_async(swp_entry_t entry, gfp_t gfp_mask,
> goto put_and_return;
>
> /*
> - * We might race against __delete_from_swap_cache(), and
> + * We might race against __swap_cache_del_folio(), 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
> @@ -405,8 +432,7 @@ struct folio *__read_swap_cache_async(swp_entry_t entry, gfp_t gfp_mask,
> 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))
> + if (swap_cache_add_folio(entry, new_folio, &shadow))
> goto fail_unlock;
>
> memcg1_swapin(entry, 1);
> @@ -572,11 +598,11 @@ struct folio *swap_cluster_readahead(swp_entry_t entry, gfp_t gfp_mask,
> end_offset = si->max - 1;
>
> blk_start_plug(&plug);
> - for (offset = start_offset; offset <= end_offset ; offset++) {
> + 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);
> + swp_entry(swp_type(entry), offset), gfp_mask, mpol, ilx,
> + &page_allocated, false);
> if (!folio)
> continue;
> if (page_allocated) {
> @@ -600,41 +626,6 @@ struct folio *swap_cluster_readahead(swp_entry_t entry, gfp_t gfp_mask,
> 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)
> {
> @@ -807,7 +798,7 @@ static const struct attribute_group swap_attr_group = {
> .attrs = swap_attrs,
> };
>
> -static int __init swap_init_sysfs(void)
> +static int __init swap_init(void)
> {
> int err;
> struct kobject *swap_kobj;
> @@ -822,11 +813,13 @@ static int __init swap_init_sysfs(void)
> pr_err("failed to register swap group\n");
> goto delete_obj;
> }
> + /* swap_space is set RO after init, so do it here before init ends. */
> + mapping_set_no_writeback_tags(&swap_space);
> return 0;
>
> delete_obj:
> kobject_put(swap_kobj);
> return err;
> }
> -subsys_initcall(swap_init_sysfs);
> +subsys_initcall(swap_init);
> #endif
> diff --git a/mm/swap_table.h b/mm/swap_table.h
> new file mode 100644
> index 000000000000..ed9676547071
> --- /dev/null
> +++ b/mm/swap_table.h
> @@ -0,0 +1,106 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +#ifndef _MM_SWAP_TABLE_H
> +#define _MM_SWAP_TABLE_H
> +
> +#include "swap.h"
> +
> +/*
> + * A swap table entry represents the status of a swap slot on a swap
> + * (physical or virtual) device. The swap table in each cluster is a
> + * 1:1 map of the swap slots in this cluster.
> + *
> + * Each swap table entry could be a pointer (folio), a XA_VALUE
> + * (shadow), or NULL.
> + */
> +
> +/*
> + * Helpers for casting one type of info into a swap table entry.
> + */
> +static inline unsigned long null_to_swp_tb(void)
> +{
> + BUILD_BUG_ON(sizeof(unsigned long) != sizeof(atomic_long_t));
> + return 0;
> +}
> +
> +static inline unsigned long folio_to_swp_tb(struct folio *folio)
> +{
> + BUILD_BUG_ON(sizeof(unsigned long) != sizeof(void *));
> + return (unsigned long)folio;
> +}
> +
> +static inline unsigned long shadow_swp_to_tb(void *shadow)
> +{
> + BUILD_BUG_ON((BITS_PER_XA_VALUE + 1) !=
> + BITS_PER_BYTE * sizeof(unsigned long));
> + VM_WARN_ON_ONCE(shadow && !xa_is_value(shadow));
> + return (unsigned long)shadow;
> +}
> +
> +/*
> + * Helpers for swap table entry type checking.
> + */
> +static inline bool swp_tb_is_null(unsigned long swp_tb)
> +{
> + return !swp_tb;
> +}
> +
> +static inline bool swp_tb_is_folio(unsigned long swp_tb)
> +{
> + return !xa_is_value((void *)swp_tb) && !swp_tb_is_null(swp_tb);
> +}
> +
> +static inline bool swp_tb_is_shadow(unsigned long swp_tb)
> +{
> + return xa_is_value((void *)swp_tb);
> +}
> +
> +/*
> + * Helpers for retrieving info from swap table.
> + */
> +static inline struct folio *swp_tb_to_folio(unsigned long swp_tb)
> +{
> + VM_WARN_ON(!swp_tb_is_folio(swp_tb));
> + return (void *)swp_tb;
> +}
> +
> +static inline void *swp_tb_to_shadow(unsigned long swp_tb)
> +{
> + VM_WARN_ON(!swp_tb_is_shadow(swp_tb));
> + return (void *)swp_tb;
> +}
> +
> +/*
> + * Helpers for accessing or modifying the swap table of a cluster,
> + * the swap cluster must be locked.
> + */
> +static inline void __swap_table_set(struct swap_cluster_info *ci,
> + unsigned int off, unsigned long swp_tb)
> +{
> + VM_WARN_ON_ONCE(off >= SWAPFILE_CLUSTER);
> + atomic_long_set(&ci->table[off], swp_tb);
> +}
> +
> +static inline unsigned long __swap_table_get(struct swap_cluster_info *ci,
> + unsigned int off)
> +{
> + VM_WARN_ON_ONCE(off >= SWAPFILE_CLUSTER);
> + return atomic_long_read(&ci->table[off]);
> +}
> +
> +static inline void __swap_table_set_folio(struct swap_cluster_info *ci,
> + unsigned int off, struct folio *folio)
> +{
> + __swap_table_set(ci, off, folio_to_swp_tb(folio));
> +}
> +
> +static inline void __swap_table_set_shadow(struct swap_cluster_info *ci,
> + unsigned int off, void *shadow)
> +{
> + __swap_table_set(ci, off, shadow_swp_to_tb(shadow));
> +}
> +
> +static inline void __swap_table_init_null(struct swap_cluster_info *ci, unsigned int off)
> +{
> + __swap_table_set(ci, off, null_to_swp_tb());
> +}
> +#endif
> diff --git a/mm/swapfile.c b/mm/swapfile.c
> index 85606fbebf0f..df68b5e242a6 100644
> --- a/mm/swapfile.c
> +++ b/mm/swapfile.c
> @@ -46,6 +46,7 @@
> #include <asm/tlbflush.h>
> #include <linux/swapops.h>
> #include <linux/swap_cgroup.h>
> +#include "swap_table.h"
> #include "internal.h"
> #include "swap.h"
>
> @@ -268,7 +269,7 @@ static int __try_to_reclaim_swap(struct swap_info_struct *si,
> if (!need_reclaim)
> goto out_unlock;
>
> - delete_from_swap_cache(folio);
> + swap_cache_del_folio(folio);
> folio_set_dirty(folio);
> ret = nr_pages;
> out_unlock:
> @@ -422,6 +423,34 @@ static inline unsigned int cluster_offset(struct swap_info_struct *si,
> return cluster_index(si, ci) * SWAPFILE_CLUSTER;
> }
>
> +static int swap_table_alloc_table(struct swap_cluster_info *ci)
> +{
> + WARN_ON(ci->table);
> + ci->table = kzalloc(sizeof(unsigned long) * SWAPFILE_CLUSTER, GFP_KERNEL);
> + if (!ci->table)
> + return -ENOMEM;
> + return 0;
> +}
> +
> +static void swap_cluster_free_table(struct swap_cluster_info *ci)
> +{
> + unsigned int ci_off;
> + unsigned long swp_tb;
> +
> + if (!ci->table)
> + return;
> +
> + for (ci_off = 0; ci_off < SWAPFILE_CLUSTER; ci_off++) {
> + swp_tb = __swap_table_get(ci, ci_off);
> + if (!swp_tb_is_null(swp_tb))
> + pr_err_once("swap: unclean swap space on swapoff: 0x%lx",
> + swp_tb);
> + }
> +
> + kfree(ci->table);
> + ci->table = NULL;
> +}
> +
> static void move_cluster(struct swap_info_struct *si,
> struct swap_cluster_info *ci, struct list_head *list,
> enum swap_cluster_flags new_flags)
> @@ -704,6 +733,25 @@ static bool cluster_scan_range(struct swap_info_struct *si,
> return true;
> }
>
> +/*
> + * Currently, the swap table is not used for count tracking,
> + * just do a sanity check to ensure nothing went wrong.
> + */
> +static void cluster_table_check(struct swap_cluster_info *ci,
> + unsigned int start, unsigned int nr)
> +{
> + unsigned int ci_off = start % SWAPFILE_CLUSTER;
> + unsigned int ci_end = ci_off + nr;
> + unsigned long swp_tb;
> +
> + if (IS_ENABLED(CONFIG_DEBUG_VM)) {
> + do {
> + swp_tb = __swap_table_get(ci, ci_off);
> + VM_WARN_ON_ONCE(!swp_tb_is_null(swp_tb));
> + } while (++ci_off < ci_end);
> + }
> +}
> +
> static bool cluster_alloc_range(struct swap_info_struct *si, struct swap_cluster_info *ci,
> unsigned int start, unsigned char usage,
> unsigned int order)
> @@ -723,6 +771,7 @@ static bool cluster_alloc_range(struct swap_info_struct *si, struct swap_cluster
> ci->order = order;
>
> memset(si->swap_map + start, usage, nr_pages);
> + cluster_table_check(ci, start, nr_pages);
> swap_range_alloc(si, nr_pages);
> ci->count += nr_pages;
>
> @@ -1100,8 +1149,7 @@ static void swap_range_alloc(struct swap_info_struct *si,
> static void swap_range_free(struct swap_info_struct *si, unsigned long offset,
> unsigned int nr_entries)
> {
> - unsigned long begin = offset;
> - unsigned long end = offset + nr_entries - 1;
> + unsigned long start = offset, end = offset + nr_entries - 1;
And this kind of clean up or code style adjustment, adding them here will
distract people from focusing on swap table introducing.
> void (*swap_slot_free_notify)(struct block_device *, unsigned long);
> unsigned int i;
>
> @@ -1125,7 +1173,7 @@ static void swap_range_free(struct swap_info_struct *si, unsigned long offset,
> swap_slot_free_notify(si->bdev, offset);
> offset++;
> }
> - clear_shadow_from_swap_cache(si->type, begin, end);
> + __swap_cache_clear_shadow(swp_entry(si->type, start), nr_entries);
>
> /*
> * Make sure that try_to_unuse() observes si->inuse_pages reaching 0
> @@ -1282,15 +1330,7 @@ int folio_alloc_swap(struct folio *folio, gfp_t gfp)
> if (!entry.val)
> return -ENOMEM;
>
> - /*
> - * 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.
> - */
> - if (add_to_swap_cache(folio, entry, gfp | __GFP_NOMEMALLOC, NULL))
> + if (swap_cache_add_folio(entry, folio, NULL))
> goto out_free;
>
> return 0;
> @@ -1557,6 +1597,7 @@ static void swap_entries_free(struct swap_info_struct *si,
>
> mem_cgroup_uncharge_swap(entry, nr_pages);
> swap_range_free(si, offset, nr_pages);
> + cluster_table_check(ci, offset, nr_pages);
>
> if (!ci->count)
> free_cluster(si, ci);
> @@ -1760,7 +1801,7 @@ bool folio_free_swap(struct folio *folio)
> if (folio_swapped(folio))
> return false;
>
> - delete_from_swap_cache(folio);
> + swap_cache_del_folio(folio);
> folio_set_dirty(folio);
> return true;
> }
> @@ -2634,6 +2675,18 @@ static void wait_for_allocation(struct swap_info_struct *si)
> }
> }
>
> +static void free_cluster_info(struct swap_cluster_info *cluster_info,
> + unsigned long maxpages)
> +{
> + int i, nr_clusters = DIV_ROUND_UP(maxpages, SWAPFILE_CLUSTER);
> +
> + if (!cluster_info)
> + return;
> + for (i = 0; i < nr_clusters; i++)
> + swap_cluster_free_table(&cluster_info[i]);
> + kvfree(cluster_info);
> +}
> +
> /*
> * Called after swap device's reference count is dead, so
> * neither scan nor allocation will use it.
> @@ -2768,12 +2821,13 @@ SYSCALL_DEFINE1(swapoff, const char __user *, specialfile)
>
> swap_file = p->swap_file;
> p->swap_file = NULL;
> - p->max = 0;
> swap_map = p->swap_map;
> p->swap_map = NULL;
> zeromap = p->zeromap;
> p->zeromap = NULL;
> cluster_info = p->cluster_info;
> + free_cluster_info(cluster_info, p->max);
> + p->max = 0;
> p->cluster_info = NULL;
> spin_unlock(&p->lock);
> spin_unlock(&swap_lock);
> @@ -2784,10 +2838,8 @@ SYSCALL_DEFINE1(swapoff, const char __user *, specialfile)
> p->global_cluster = NULL;
> vfree(swap_map);
> kvfree(zeromap);
> - kvfree(cluster_info);
> /* Destroy swap account information */
> swap_cgroup_swapoff(p->type);
> - exit_swap_address_space(p->type);
>
> inode = mapping->host;
>
> @@ -3171,8 +3223,11 @@ static struct swap_cluster_info *setup_clusters(struct swap_info_struct *si,
> if (!cluster_info)
> goto err;
>
> - for (i = 0; i < nr_clusters; i++)
> + for (i = 0; i < nr_clusters; i++) {
> spin_lock_init(&cluster_info[i].lock);
> + if (swap_table_alloc_table(&cluster_info[i]))
> + goto err_free;
> + }
>
> if (!(si->flags & SWP_SOLIDSTATE)) {
> si->global_cluster = kmalloc(sizeof(*si->global_cluster),
> @@ -3233,9 +3288,8 @@ static struct swap_cluster_info *setup_clusters(struct swap_info_struct *si,
> }
>
> return cluster_info;
> -
> err_free:
> - kvfree(cluster_info);
> + free_cluster_info(cluster_info, maxpages);
> err:
> return ERR_PTR(err);
> }
> @@ -3429,13 +3483,9 @@ SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags)
> }
> }
>
> - error = init_swap_address_space(si->type, maxpages);
> - if (error)
> - goto bad_swap_unlock_inode;
> -
> error = zswap_swapon(si->type, maxpages);
> if (error)
> - goto free_swap_address_space;
> + goto bad_swap_unlock_inode;
>
> /*
> * Flush any pending IO and dirty mappings before we start using this
> @@ -3470,8 +3520,6 @@ SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags)
> goto out;
> free_swap_zswap:
> zswap_swapoff(si->type);
> -free_swap_address_space:
> - exit_swap_address_space(si->type);
> bad_swap_unlock_inode:
> inode_unlock(inode);
> bad_swap:
> @@ -3486,7 +3534,8 @@ SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags)
> spin_unlock(&swap_lock);
> vfree(swap_map);
> kvfree(zeromap);
> - kvfree(cluster_info);
> + if (cluster_info)
> + free_cluster_info(cluster_info, maxpages);
> if (inced_nr_rotate_swap)
> atomic_dec(&nr_rotate_swap);
> if (swap_file)
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index b0afd7f41a22..1ed3cf9dac4e 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -730,13 +730,18 @@ static int __remove_mapping(struct address_space *mapping, struct folio *folio,
> {
> int refcount;
> void *shadow = NULL;
> + struct swap_cluster_info *ci;
>
> BUG_ON(!folio_test_locked(folio));
> BUG_ON(mapping != folio_mapping(folio));
>
> - if (!folio_test_swapcache(folio))
> + if (folio_test_swapcache(folio)) {
> + ci = swap_cluster_lock_by_folio_irq(folio);
> + } else {
> spin_lock(&mapping->host->i_lock);
> - xa_lock_irq(&mapping->i_pages);
> + xa_lock_irq(&mapping->i_pages);
> + }
> +
> /*
> * The non racy check for a busy folio.
> *
> @@ -776,9 +781,9 @@ static int __remove_mapping(struct address_space *mapping, struct folio *folio,
>
> if (reclaimed && !mapping_exiting(mapping))
> shadow = workingset_eviction(folio, target_memcg);
> - __delete_from_swap_cache(folio, swap, shadow);
> + __swap_cache_del_folio(swap, folio, shadow);
> memcg1_swapout(folio, swap);
> - xa_unlock_irq(&mapping->i_pages);
> + swap_cluster_unlock_irq(ci);
> put_swap_folio(folio, swap);
> } else {
> void (*free_folio)(struct folio *);
> @@ -816,9 +821,12 @@ static int __remove_mapping(struct address_space *mapping, struct folio *folio,
> return 1;
>
> cannot_free:
> - xa_unlock_irq(&mapping->i_pages);
> - if (!folio_test_swapcache(folio))
> + if (folio_test_swapcache(folio)) {
> + swap_cluster_unlock_irq(ci);
> + } else {
> + xa_unlock_irq(&mapping->i_pages);
> spin_unlock(&mapping->host->i_lock);
> + }
> return 0;
> }
>
> diff --git a/mm/zswap.c b/mm/zswap.c
> index ee443b317ac7..c869859eec77 100644
> --- a/mm/zswap.c
> +++ b/mm/zswap.c
> @@ -1166,7 +1166,7 @@ static int zswap_writeback_entry(struct zswap_entry *entry,
>
> out:
> if (ret && ret != -EEXIST) {
> - delete_from_swap_cache(folio);
> + swap_cache_del_folio(folio);
> folio_unlock(folio);
> }
> folio_put(folio);
> --
> 2.51.0
>
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