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Message-ID: <20240610121820.328876-3-usamaarif642@gmail.com>
Date: Mon, 10 Jun 2024 13:16:00 +0100
From: Usama Arif <usamaarif642@...il.com>
To: akpm@...ux-foundation.org
Cc: hannes@...xchg.org,
david@...hat.com,
ying.huang@...el.com,
hughd@...gle.com,
willy@...radead.org,
yosryahmed@...gle.com,
nphamcs@...il.com,
chengming.zhou@...ux.dev,
linux-mm@...ck.org,
linux-kernel@...r.kernel.org,
kernel-team@...a.com,
Usama Arif <usamaarif642@...il.com>
Subject: [PATCH v3 2/2] 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.
Signed-off-by: Usama Arif <usamaarif642@...il.com>
---
mm/zswap.c | 86 +++++-------------------------------------------------
1 file changed, 8 insertions(+), 78 deletions(-)
diff --git a/mm/zswap.c b/mm/zswap.c
index b9b35ef86d9b..ca8df9c99abf 100644
--- 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
@@ -182,11 +180,9 @@ 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.
* pool - the zswap_pool the entry's data is in
* handle - zpool allocation handle that stores the compressed page data
- * value - value of the same-value filled pages which have same content
* objcg - the obj_cgroup that the compressed memory is charged to
* lru - handle to the pool's lru used to evict pages.
*/
@@ -194,10 +190,7 @@ struct zswap_entry {
swp_entry_t swpentry;
unsigned int length;
struct zswap_pool *pool;
- union {
- unsigned long handle;
- unsigned long value;
- };
+ unsigned long handle;
struct obj_cgroup *objcg;
struct list_head lru;
};
@@ -814,13 +807,9 @@ static struct zpool *zswap_find_zpool(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(zswap_find_zpool(entry), entry->handle);
- zswap_pool_put(entry->pool);
- }
+ zswap_lru_del(&zswap_list_lru, entry);
+ zpool_free(zswap_find_zpool(entry), entry->handle);
+ zswap_pool_put(entry->pool);
if (entry->objcg) {
obj_cgroup_uncharge_zswap(entry->objcg, entry->length);
obj_cgroup_put(entry->objcg);
@@ -1262,11 +1251,6 @@ 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);
}
@@ -1370,42 +1354,6 @@ static void shrink_worker(struct work_struct *w)
} 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
**********************************/
@@ -1417,7 +1365,6 @@ 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));
@@ -1450,13 +1397,6 @@ 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)
@@ -1474,7 +1414,6 @@ bool zswap_store(struct folio *folio)
if (!zswap_compress(folio, entry))
goto put_pool;
-store_entry:
entry->swpentry = swp;
entry->objcg = objcg;
@@ -1522,13 +1461,9 @@ bool zswap_store(struct folio *folio)
return true;
store_failed:
- if (!entry->length)
- atomic_dec(&zswap_same_filled_pages);
- else {
- zpool_free(zswap_find_zpool(entry), entry->handle);
+ zpool_free(zswap_find_zpool(entry), entry->handle);
put_pool:
- zswap_pool_put(entry->pool);
- }
+ zswap_pool_put(entry->pool);
freepage:
zswap_entry_cache_free(entry);
reject:
@@ -1577,10 +1512,7 @@ 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)
@@ -1682,8 +1614,6 @@ 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;
}
--
2.43.0
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