mm: swap: add nr argument in swapcache_prepare and swapcache_clear to support large...

Right now, swapcache_prepare() and swapcache_clear() supports one entry
only, to support large folios, we need to handle multiple swap entries.

To optimize stack usage, we iterate twice in __swap_duplicate(): the first
time to verify that all entries are valid, and the second time to apply
the modifications to the entries.

Currently, we're using nr=1 for the existing users.

[v-songbaohua@oppo.com: clarify swap_count_continued and improve readability for  __swap_duplicate]
Link: https://lkml.kernel.org/r/20240802071817.47081-1-21cnbao@gmail.com
Link: https://lkml.kernel.org/r/20240730071339.107447-2-21cnbao@gmail.com
Signed-off-by: Barry Song <v-songbaohua@oppo.com>
Reviewed-by: Baolin Wang <baolin.wang@linux.alibaba.com>
Acked-by: David Hildenbrand <david@redhat.com>
Tested-by: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: Chris Li <chrisl@kernel.org>
Cc: Gao Xiang <xiang@kernel.org>
Cc: "Huang, Ying" <ying.huang@intel.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Kairui Song <kasong@tencent.com>
Cc: Kalesh Singh <kaleshsingh@google.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Nhat Pham <nphamcs@gmail.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Sergey Senozhatsky <senozhatsky@chromium.org>
Cc: Shakeel Butt <shakeel.butt@linux.dev>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Yang Shi <shy828301@gmail.com>
Cc: Yosry Ahmed <yosryahmed@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/include/linux/swap.h b/include/linux/swap.h
index ba7ea95d1c57a51fa2ccb090096539a90e2db3e5..5b920fa2315b1399cc1362ea5bb74de2a12641cd 100644 (file)
--- a/include/linux/swap.h
+++ b/include/linux/swap.h
@@ -480,7 +480,7 @@ extern int get_swap_pages(int n, swp_entry_t swp_entries[], int order);
 extern int add_swap_count_continuation(swp_entry_t, gfp_t);
 extern void swap_shmem_alloc(swp_entry_t);
 extern int swap_duplicate(swp_entry_t);
-extern int swapcache_prepare(swp_entry_t);
+extern int swapcache_prepare(swp_entry_t entry, int nr);
 extern void swap_free_nr(swp_entry_t entry, int nr_pages);
 extern void swapcache_free_entries(swp_entry_t *entries, int n);
 extern void free_swap_and_cache_nr(swp_entry_t entry, int nr);
@@ -554,7 +554,7 @@ static inline int swap_duplicate(swp_entry_t swp)
        return 0;
 }
 
-static inline int swapcache_prepare(swp_entry_t swp)
+static inline int swapcache_prepare(swp_entry_t swp, int nr)
 {
        return 0;
 }

diff --git a/mm/memory.c b/mm/memory.c
index 71236ae6fd144f04a2fd44fbb4545a65c0be424c..cacf03bbdd7abea55c6d11f970633da0e4c37de7 100644 (file)
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -4081,7 +4081,7 @@ vm_fault_t do_swap_page(struct vm_fault *vmf)
                         * reusing the same entry. It's undetectable as
                         * pte_same() returns true due to entry reuse.
                         */
-                       if (swapcache_prepare(entry)) {
+                       if (swapcache_prepare(entry, 1)) {
                                /* Relax a bit to prevent rapid repeated page faults */
                                schedule_timeout_uninterruptible(1);
                                goto out;
@@ -4387,7 +4387,7 @@ unlock:
 out:
        /* Clear the swap cache pin for direct swapin after PTL unlock */
        if (need_clear_cache)
-               swapcache_clear(si, entry);
+               swapcache_clear(si, entry, 1);
        if (si)
                put_swap_device(si);
        return ret;
@@ -4403,7 +4403,7 @@ out_release:
                folio_put(swapcache);
        }
        if (need_clear_cache)
-               swapcache_clear(si, entry);
+               swapcache_clear(si, entry, 1);
        if (si)
                put_swap_device(si);
        return ret;

diff --git a/mm/swap.h b/mm/swap.h
index baa1fa946b347b3464962283160f8bd9cf6e9bf0..7c6330561d84b8138616884a50f14957174156d6 100644 (file)
--- a/mm/swap.h
+++ b/mm/swap.h
@@ -59,7 +59,7 @@ void __delete_from_swap_cache(struct folio *folio,
 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);
+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 vm_area_struct *vma, unsigned long addr);
 struct folio *filemap_get_incore_folio(struct address_space *mapping,
@@ -120,7 +120,7 @@ static inline int swap_writepage(struct page *p, struct writeback_control *wbc)
        return 0;
 }
 
-static inline void swapcache_clear(struct swap_info_struct *si, swp_entry_t entry)
+static inline void swapcache_clear(struct swap_info_struct *si, swp_entry_t entry, int nr)
 {
 }
 
@@ -172,4 +172,5 @@ static inline unsigned int folio_swap_flags(struct folio *folio)
        return 0;
 }
 #endif /* CONFIG_SWAP */
+
 #endif /* _MM_SWAP_H */

diff --git a/mm/swap_state.c b/mm/swap_state.c
index a1726e49a5eb6b5d71c715cf614c2e25f096bd85..b06f2a054f5ac082e6c0d00119a52250918ac486 100644 (file)
--- a/mm/swap_state.c
+++ b/mm/swap_state.c
@@ -477,7 +477,7 @@ struct folio *__read_swap_cache_async(swp_entry_t entry, gfp_t gfp_mask,
                /*
                 * Swap entry may have been freed since our caller observed it.
                 */
-               err = swapcache_prepare(entry);
+               err = swapcache_prepare(entry, 1);
                if (!err)
                        break;
 

diff --git a/mm/swapfile.c b/mm/swapfile.c
index 5f73a85533713792cd60c692ba565d5fa2f9ad91..0259f36de715f529e9ee980c28f97ee244d4dd41 100644 (file)
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -3363,7 +3363,7 @@ void si_swapinfo(struct sysinfo *val)
 }
 
 /*
- * Verify that a swap entry is valid and increment its swap map count.
+ * Verify that nr swap entries are valid and increment their swap map counts.
  *
  * Returns error code in following case.
  * - success -> 0
@@ -3373,60 +3373,73 @@ void si_swapinfo(struct sysinfo *val)
  * - swap-cache reference is requested but the entry is not used. -> ENOENT
  * - swap-mapped reference requested but needs continued swap count. -> ENOMEM
  */
-static int __swap_duplicate(swp_entry_t entry, unsigned char usage)
+static int __swap_duplicate(swp_entry_t entry, unsigned char usage, int nr)
 {
        struct swap_info_struct *p;
        struct swap_cluster_info *ci;
        unsigned long offset;
        unsigned char count;
        unsigned char has_cache;
-       int err;
+       int err, i;
 
        p = swp_swap_info(entry);
 
        offset = swp_offset(entry);
+       VM_WARN_ON(nr > SWAPFILE_CLUSTER - offset % SWAPFILE_CLUSTER);
+       VM_WARN_ON(usage == 1 && nr > 1);
        ci = lock_cluster_or_swap_info(p, offset);
 
-       count = p->swap_map[offset];
-
-       /*
-        * swapin_readahead() doesn't check if a swap entry is valid, so the
-        * swap entry could be SWAP_MAP_BAD. Check here with lock held.
-        */
-       if (unlikely(swap_count(count) == SWAP_MAP_BAD)) {
-               err = -ENOENT;
-               goto unlock_out;
-       }
-
-       has_cache = count & SWAP_HAS_CACHE;
-       count &= ~SWAP_HAS_CACHE;
        err = 0;
+       for (i = 0; i < nr; i++) {
+               count = p->swap_map[offset + i];
 
-       if (usage == SWAP_HAS_CACHE) {
+               /*
+                * swapin_readahead() doesn't check if a swap entry is valid, so the
+                * swap entry could be SWAP_MAP_BAD. Check here with lock held.
+                */
+               if (unlikely(swap_count(count) == SWAP_MAP_BAD)) {
+                       err = -ENOENT;
+                       goto unlock_out;
+               }
 
-               /* set SWAP_HAS_CACHE if there is no cache and entry is used */
-               if (!has_cache && count)
-                       has_cache = SWAP_HAS_CACHE;
-               else if (has_cache)             /* someone else added cache */
-                       err = -EEXIST;
-               else                            /* no users remaining */
+               has_cache = count & SWAP_HAS_CACHE;
+               count &= ~SWAP_HAS_CACHE;
+
+               if (!count && !has_cache) {
                        err = -ENOENT;
+               } else if (usage == SWAP_HAS_CACHE) {
+                       if (has_cache)
+                               err = -EEXIST;
+               } else if ((count & ~COUNT_CONTINUED) > SWAP_MAP_MAX) {
+                       err = -EINVAL;
+               }
+
+               if (err)
+                       goto unlock_out;
+       }
 
-       } else if (count || has_cache) {
+       for (i = 0; i < nr; i++) {
+               count = p->swap_map[offset + i];
+               has_cache = count & SWAP_HAS_CACHE;
+               count &= ~SWAP_HAS_CACHE;
 
-               if ((count & ~COUNT_CONTINUED) < SWAP_MAP_MAX)
+               if (usage == SWAP_HAS_CACHE)
+                       has_cache = SWAP_HAS_CACHE;
+               else if ((count & ~COUNT_CONTINUED) < SWAP_MAP_MAX)
                        count += usage;
-               else if ((count & ~COUNT_CONTINUED) > SWAP_MAP_MAX)
-                       err = -EINVAL;
-               else if (swap_count_continued(p, offset, count))
+               else if (swap_count_continued(p, offset + i, count))
                        count = COUNT_CONTINUED;
-               else
+               else {
+                       /*
+                        * Don't need to rollback changes, because if
+                        * usage == 1, there must be nr == 1.
+                        */
                        err = -ENOMEM;
-       } else
-               err = -ENOENT;                  /* unused swap entry */
+                       goto unlock_out;
+               }
 
-       if (!err)
-               WRITE_ONCE(p->swap_map[offset], count | has_cache);
+               WRITE_ONCE(p->swap_map[offset + i], count | has_cache);
+       }
 
 unlock_out:
        unlock_cluster_or_swap_info(p, ci);
@@ -3439,7 +3452,7 @@ unlock_out:
  */
 void swap_shmem_alloc(swp_entry_t entry)
 {
-       __swap_duplicate(entry, SWAP_MAP_SHMEM);
+       __swap_duplicate(entry, SWAP_MAP_SHMEM, 1);
 }
 
 /*
@@ -3453,29 +3466,29 @@ int swap_duplicate(swp_entry_t entry)
 {
        int err = 0;
 
-       while (!err && __swap_duplicate(entry, 1) == -ENOMEM)
+       while (!err && __swap_duplicate(entry, 1, 1) == -ENOMEM)
                err = add_swap_count_continuation(entry, GFP_ATOMIC);
        return err;
 }
 
 /*
- * @entry: swap entry for which we allocate swap cache.
+ * @entry: first swap entry from which we allocate nr swap cache.
  *
- * Called when allocating swap cache for existing swap entry,
+ * Called when allocating swap cache for existing swap entries,
  * This can return error codes. Returns 0 at success.
  * -EEXIST means there is a swap cache.
  * Note: return code is different from swap_duplicate().
  */
-int swapcache_prepare(swp_entry_t entry)
+int swapcache_prepare(swp_entry_t entry, int nr)
 {
-       return __swap_duplicate(entry, SWAP_HAS_CACHE);
+       return __swap_duplicate(entry, SWAP_HAS_CACHE, nr);
 }
 
-void swapcache_clear(struct swap_info_struct *si, swp_entry_t entry)
+void swapcache_clear(struct swap_info_struct *si, swp_entry_t entry, int nr)
 {
        unsigned long offset = swp_offset(entry);
 
-       cluster_swap_free_nr(si, offset, 1, SWAP_HAS_CACHE);
+       cluster_swap_free_nr(si, offset, nr, SWAP_HAS_CACHE);
 }
 
 struct swap_info_struct *swp_swap_info(swp_entry_t entry)