mm: remove code to handle same filled pages

With an earlier commit to handle zero-filled pages in swap directly, and
with only 1% of the same-filled pages being non-zero, zswap no longer
needs to handle same-filled pages and can just work on compressed pages.

Link: https://lkml.kernel.org/r/20240823190545.979059-3-usamaarif642@gmail.com
Signed-off-by: Usama Arif <usamaarif642@gmail.com>
Reviewed-by: Chengming Zhou <chengming.zhou@linux.dev>
Acked-by: Yosry Ahmed <yosryahmed@google.com>
Reviewed-by: Nhat Pham <nphamcs@gmail.com>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Shakeel Butt <shakeel.butt@linux.dev>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/mm/zswap.c b/mm/zswap.c
index df66ab102d2765da8d93ba75006a3d580fefc621..449914ea99198abdc60dbe676d228b9725244a9f 100644 (file)
--- a/mm/zswap.c
+++ b/mm/zswap.c
@@ -44,8 +44,6 @@
 **********************************/
 /* The number of compressed pages currently stored in zswap */
 atomic_t zswap_stored_pages = ATOMIC_INIT(0);
-/* The number of same-value filled pages currently stored in zswap */
-static atomic_t zswap_same_filled_pages = ATOMIC_INIT(0);
 
 /*
  * The statistics below are not protected from concurrent access for
@@ -185,8 +183,7 @@ static struct shrinker *zswap_shrinker;
  *
  * swpentry - associated swap entry, the offset indexes into the red-black tree
  * length - the length in bytes of the compressed page data.  Needed during
- *          decompression. For a same value filled page length is 0, and both
- *          pool and lru are invalid and must be ignored.
+ *          decompression.
  * referenced - true if the entry recently entered the zswap pool. Unset by the
  *              writeback logic. The entry is only reclaimed by the writeback
  *              logic if referenced is unset. See comments in the shrinker
@@ -202,10 +199,7 @@ struct zswap_entry {
        unsigned int length;
        bool referenced;
        struct zswap_pool *pool;
-       union {
-               unsigned long handle;
-               unsigned long value;
-       };
+       unsigned long handle;
        struct obj_cgroup *objcg;
        struct list_head lru;
 };
@@ -801,13 +795,9 @@ static void zswap_entry_cache_free(struct zswap_entry *entry)
  */
 static void zswap_entry_free(struct zswap_entry *entry)
 {
-       if (!entry->length)
-               atomic_dec(&zswap_same_filled_pages);
-       else {
-               zswap_lru_del(&zswap_list_lru, entry);
-               zpool_free(entry->pool->zpool, entry->handle);
-               zswap_pool_put(entry->pool);
-       }
+       zswap_lru_del(&zswap_list_lru, entry);
+       zpool_free(entry->pool->zpool, entry->handle);
+       zswap_pool_put(entry->pool);
        if (entry->objcg) {
                obj_cgroup_uncharge_zswap(entry->objcg, entry->length);
                obj_cgroup_put(entry->objcg);
@@ -1277,11 +1267,6 @@ static unsigned long zswap_shrinker_count(struct shrinker *shrinker,
         * This ensures that the better zswap compresses memory, the fewer
         * pages we will evict to swap (as it will otherwise incur IO for
         * relatively small memory saving).
-        *
-        * The memory saving factor calculated here takes same-filled pages into
-        * account, but those are not freeable since they almost occupy no
-        * space. Hence, we may scale nr_freeable down a little bit more than we
-        * should if we have a lot of same-filled pages.
         */
        return mult_frac(nr_freeable, nr_backing, nr_stored);
 }
@@ -1416,42 +1401,6 @@ resched:
        } while (zswap_total_pages() > thr);
 }
 
-/*********************************
-* same-filled functions
-**********************************/
-static bool zswap_is_folio_same_filled(struct folio *folio, unsigned long *value)
-{
-       unsigned long *data;
-       unsigned long val;
-       unsigned int pos, last_pos = PAGE_SIZE / sizeof(*data) - 1;
-       bool ret = false;
-
-       data = kmap_local_folio(folio, 0);
-       val = data[0];
-
-       if (val != data[last_pos])
-               goto out;
-
-       for (pos = 1; pos < last_pos; pos++) {
-               if (val != data[pos])
-                       goto out;
-       }
-
-       *value = val;
-       ret = true;
-out:
-       kunmap_local(data);
-       return ret;
-}
-
-static void zswap_fill_folio(struct folio *folio, unsigned long value)
-{
-       unsigned long *data = kmap_local_folio(folio, 0);
-
-       memset_l(data, value, PAGE_SIZE / sizeof(unsigned long));
-       kunmap_local(data);
-}
-
 /*********************************
 * main API
 **********************************/
@@ -1463,7 +1412,6 @@ bool zswap_store(struct folio *folio)
        struct zswap_entry *entry, *old;
        struct obj_cgroup *objcg = NULL;
        struct mem_cgroup *memcg = NULL;
-       unsigned long value;
 
        VM_WARN_ON_ONCE(!folio_test_locked(folio));
        VM_WARN_ON_ONCE(!folio_test_swapcache(folio));
@@ -1496,13 +1444,6 @@ bool zswap_store(struct folio *folio)
                goto reject;
        }
 
-       if (zswap_is_folio_same_filled(folio, &value)) {
-               entry->length = 0;
-               entry->value = value;
-               atomic_inc(&zswap_same_filled_pages);
-               goto store_entry;
-       }
-
        /* if entry is successfully added, it keeps the reference */
        entry->pool = zswap_pool_current_get();
        if (!entry->pool)
@@ -1520,7 +1461,6 @@ bool zswap_store(struct folio *folio)
        if (!zswap_compress(folio, entry))
                goto put_pool;
 
-store_entry:
        entry->swpentry = swp;
        entry->objcg = objcg;
        entry->referenced = true;
@@ -1569,13 +1509,9 @@ store_entry:
        return true;
 
 store_failed:
-       if (!entry->length)
-               atomic_dec(&zswap_same_filled_pages);
-       else {
-               zpool_free(entry->pool->zpool, entry->handle);
+       zpool_free(entry->pool->zpool, entry->handle);
 put_pool:
-               zswap_pool_put(entry->pool);
-       }
+       zswap_pool_put(entry->pool);
 freepage:
        zswap_entry_cache_free(entry);
 reject:
@@ -1638,10 +1574,7 @@ bool zswap_load(struct folio *folio)
        if (!entry)
                return false;
 
-       if (entry->length)
-               zswap_decompress(entry, folio);
-       else
-               zswap_fill_folio(folio, entry->value);
+       zswap_decompress(entry, folio);
 
        count_vm_event(ZSWPIN);
        if (entry->objcg)
@@ -1744,8 +1677,6 @@ static int zswap_debugfs_init(void)
                            zswap_debugfs_root, NULL, &total_size_fops);
        debugfs_create_atomic_t("stored_pages", 0444,
                                zswap_debugfs_root, &zswap_stored_pages);
-       debugfs_create_atomic_t("same_filled_pages", 0444,
-                               zswap_debugfs_root, &zswap_same_filled_pages);
 
        return 0;
 }